None of this would have been possible without the team of dedicated volunteers who submitted the bulk of the 17,000 records submitted for this project, they are too numerous to mention individually but the project is indebted to you. We would like to thank Dave Stevenson, Keith Metcalfe, Anne de Poitier, Pete Potts, John Shillitoe, Trevor Codlin, Wolfgang Ritter, Alison Giacommelli, James Parkin, Debbie King and Keith Betton for their valuable contributions at various workshops. The expert panel members; Gemma Colwell, Adam Cave, Andy Colenutt, Nick Gray, Sarah Hains, Mark Larter, David Rumble, Francesca Sanchez and Wez Smith. The project is also indebted to the team that has supported the project including Amy Brittan, Jenny Watts, Katherine Ronnie and Adam Sennitt . Special thanks also go to the SWBGS Steering Group whose collaboration has been of considerable mutual benefit. Also to Ecological Planning and Research and Chichester Harbour Conservancy for searching their archives and providing access to useful documents to complete the literature review. To Natural Aptitude and particularly Dave Kilbey for his support in developing the SolentBirds app and website. Lastly but not least we would like to thank the Environment Agency for funding and supporting this project.
Recommended Citation
Nightingale, J., Rowsell, E., Crane, H. (2022) The Solent Bird Studies: Coastal Partners.
1. Executive Summary
This report is the result of two EA/Defra Flood Defence Grant in Aid funded projects; ‘The Coastal Network Study’ and ‘The Bird Movement Study’, jointly known as the Solent Bird Studies. The study area (see figure 1.1) for the project encompasses the Solent coastline and hinterland, from Milford-on-Sea in the West to Bognor Regis in the East, including Southampton Water, Portsmouth, Langstone, Chichester and Pagham harbours, and extending south-wards to include the north coast of the Isle of Wight, From Totland to Bembridge.
It is the culmination of 4 years work including 2 full field seasons of bird surveys in the winters of 2015/16 and 2016/17, the collection of over 17,000 records and the analysis of over 40,000 bird records. The studies have;
• Developed a firm understanding of the relative site importance and a robust methodology and analysis framework for gaining this understanding for sites with insufficient data and/or in the future.
• Created a robust methodology for undertaking bird movement studies that can be delivered at the scheme level.
• Gained an understanding of bird movements and the functioning of the network through the novel use of network analysis statistics.
• Established how this relates to the importance of an individual site with a network of bird sites.
Figure 1.1 Solent Bird Studies- study area
• Therefore, providing a firm basis for taking forward current and future FCERM schemes.
Close collaboration with the Solent Waders and Brent Goose Strategy (SWBGS) Steering Group, allowed a sharing of resources and a commonality of approach, that bodes well for future work on the Solent environment and particularly in relation to over-wintering bird populations. With reducing resources and a need to share and collaborate to achieve joint aims:
• Data and approach (where compatible) was shared between Solent Bird Studies and SWBGS.
• Bird data submitted via the SolentBirds app formed a significant proportion of the new records used within the analysis for both projects.
The results of the studies have application beyond the originally conceived purpose for providing sufficient information on over-wintering birds to deliver FCERM schemes. The outputs provide useful information for bird habitat design and management, strategic plans and development control for example. The data and findings have already been used to support RHCP, local plan policies and planning proposals.
2. Background Information
2.1.
Introduction
The Solent comprises one of the most important coastal zones in the UK, for both its natural and man-made environment. An area of high socio-economic importance, with major portrelated industries and well-established industrial sectors, it also remains internationally recognised for its wildlife. However, these diverse interests make land-use planning and management increasingly complex, leading to inevitable conflict between the needs of wildlife and people.
A large number of properties within the Solent are currently at risk to coastal flooding from an extreme (1 in 200 year or 0.5% Annual Exceedance Probability (AEP)) event. Furthermore, as a result of rising sea levels due to climate change, combined with ongoing population growth, the level of coastal flood risk to the region will significantly increase if not managed sustainably. Consequently, in response to these future pressures it is recognised that significant flood and coastal erosion risk management (FCERM) schemes are required to ensure Solent communities are to be protected from coastal flooding and erosion. However, a critical issue for the implementation of these schemes is how to accommodate the increasing pressure for them without compromising the integrity of protected sites.
Coastal habitats and harbours within the Solent support a number of both nationally and internationally important populations of wintering wildfowl and waders. As a result, large areas of the coastline are designated as Special Protection Areas (SPAs) and Ramsar sites, which are accompanied by strict legal requirements to ensure all development within and outside of the site boundaries will not have any adverse effects on the protected bird populations. Furthermore, if adverse effects are unavoidable (because there are no other feasible alternatives that will have a lesser effect on the site and its features) and if there are imperative reasons of over-riding public interest (IROPI), where habitat is lost or damaged then suitable new habitat must be created as compensation. Due to its importance as an overwintering ground it is therefore essential that authorities in the Solent are able to effectively assess the impact schemes will have on protected bird populations as well as identify and secure
appropriate compensatory habitat. Migratory birds rely on the availability of a network of feeding and roosting resources over the winter period to ensure they are able to survive their long migrations. However, the importance of individual sites within this network, links between sites and the associated movement of birds is not currently well understood enough to provide sufficient evidence for clear decisions to be made regarding FCERM schemes, which could stall the process.
The Solent Bird Studies, comprised of The Solent Coastal Network Study and The Solent Bird Movement Study, are a practical attempt at addressing these issues. The Coastal Network Study aimed to develop prioritised activities and opportunities that can be undertaken by stakeholders within the Solent area to protect critically important high tide bird roosting and feeding sites while also confirming sites and techniques that have the potential to provide mitigation and compensation. The Bird Movement Study looked to improve our understanding of the ways in which birds move around between sites within the Solent, with the ultimate aim being to understand and maintain or enhance the network of environmental sites within the Solent, and the links between them. In reality during the studies the interplay between these two ‘separate’ elements was found to be inextricably linked to the understanding of the other and therefore are presented as an integrated study. Together, both projects aim to provide key information to be used for decision making to enable the on-going delivery of FCERM schemes.
2.2. Solent SPA and Ramsar designations and legislation
The Birds Directive aims to provide protection for all of the five hundred wild bird species naturally occurring in the European Union. Under Article 4 of the Directive, member states are required to classify sites which sustain rare or migratory birds as SPAs and manage these sites to a favourable condition. These can be classified under Article 4.1 for rare or vulnerable bird species listed in Annex I of the Directive or under Article 4.2 for regularly occurring migratory species or for areas which regularly support at least 20,000 waterfowl (waterfowl assemblage). Coastal habitats and harbours within the Solent support significant populations of wintering wildfowl and waders, including species listed on Annex I, as well as an average winter population of greater than 90,000 individuals (BTO WeBS Core Counts 2001-2006). As a result, four SPAs are classified within the Solent area (Figure 2.1; Appendix B) recognising its international importance as a wintering ground for migratory bird species. There is also a new SPA confirmed in 2020, the Solent and Dorset Coast to protect the shallow coastal waters that are important foraging areas for terns during the summer breeding season. Together with Special Areas of Conservation (SACs), designated under the Habitats Directive, these form part of the UKs Natura 2000 network of European sites. The Solent Bird Studies are focused on wintering wildfowl and waders and, therefore, the Solent and Dorset Coast pSPA is not considered further in this report as it is only classified for breeding terns. Whilst, the UK following Brexit and the European Union (Withdrawal) Act 2018, are no longer a member of the EU, the bird directive was transposed into law and has not been repealed.
Ramsar sites are wetlands of international importance designated under the Ramsar Convention. Ramsar sites are selected where they meet one or more of nine criteria set out in the Convention because they contain representative, rare or unique wetlands or because they are of international importance for conserving biological diversity. In the UK, the initial emphasis was on selecting sites of importance to waterbirds and consequently many Ramsar sites are also SPAs classified under the Birds Directive. There are four Ramsar sites in the Solent, which are named in accordance with their overlapping SPA, as shown in Figure 2.1
Figure 2.1 SPA and Ramsar sites : Chichester and Langstone Harbours SPA and Ramsar site, Solent and Southampton Water SPA and Ramsar site, Pagham Harbour SPA and Ramsar site and Portsmouth Harbour SPA and Ramsar site, Solent and Dorset Coast SPA
Transposed into UK law under the Conservation of Habitats and Species Regulations 2017 (commonly referred to as the Habitats Regulations), the Directives require competent authorities to assess whether a proposed development is likely to have an adverse effect on the integrity of a European site. This is achieved via a Habitats Regulations Assessment (HRA), a flow diagram of which is outlined in Appendix C. In addition to sites designated under European nature conservation legislation, United Kingdom Government policy (ODPM Circular 06/2005) states that internationally important wetlands designated under the Ramsar Convention 1971 (Ramsar sites) are afforded the same protection as SPAs and SACs for the purpose of considering plans or projects that may affect them.
The HRA process involves an initial ‘screening stage to determine whether the proposal is necessary for the management of the site or likely to have a significant effect on a European site, which in the UK includes current SPAs and SACs, as well as potential SPAs and proposed SACs, and Ramsar wetlands. The HRA needs to identify the interest features of affected European sites and whether the plan or project is likely to have a significant effect on them. It is also necessary to look at the proposed plan or project in combination with other developments in the local area. Following this, if a likely significant effect cannot be excluded, a second stage called an Appropriate Assessment (AA) is undertaken, which comprises a more detailed assessment to determine whether the plan or project will have an adverse effect on the integrity of the protected site. If necessary, avoidance or mitigation measures are included to remove the harm which otherwise would have occurred. If adverse effects are still likely after the consideration of avoidance and mitigation measures, then alternative solutions must be considered, and projects must be re-drafted to eliminate or reduce the adverse effect to below an acceptable level. Where this is not possible, a derogation can be sought under Article 6(4) of the Directive. A plan or project which results in an adverse effect on a European site can only be granted authorisation to proceed if three sequential tests are met:
• There must be no feasible alternative solutions to the plan or project which are less damaging to the affected European site(s);
• There must be “imperative reasons of overriding public interest” (IROPI) for the plan or project to proceed; and
• All necessary compensatory measures must be secured to ensure that the overall coherence of the network of European sites is protected.
2.3. Wildfowl and wading birds in the Solent
Protected species distribution and description
The Solent SPAs and Ramsar sites (Figure 2.1) are protected for a number of interest features under both Article 4.1 and Article 4.2 of the Birds Directive and under the Ramsar Convention. This includes both breeding and non-breeding (passage or over-wintering) species. Summarised below in Table 2.1 are the over-wintering interest features for all four Solent SPAs and Ramsar sites, which are the focus of these studies. The full list of interest features, both breeding and over-wintering, and their qualifying levels for the four Solent SPAs and Ramsar sites are summarised in Appendix B
Table 2.1 Summary of SPA over-wintering features in the Solent. Information in parentheses indicates whether the species is protected under Article 4.1 or Article 4.2 of the Birds Directive and/or under the Ramsar Convention.
Dunlin, Calidris alpina alpina (4.2 and Ramsar) Solent and Southampton Water SPA/Ramsar
Grey Plover, Pluvialis squatarola (4.2 and Ramsar)
Pintail, Anas acuta (4.2)
Black-tailed Godwit, Limosa limosa islandica (4.2 and Ramsar)
Dark-bellied Brent Goose, Branta bernicla bernicla (4.2 and Ramsar)
Red Breasted Merganser, Mergus serrator (4.2) Ringed Plover, Charadrius hiaticula (4.2 and Ramsar)
Redshank, Tringa totanus (4.2 and Ramsar)
Ringed Plover, Charadrius hiaticula (4.2 and Ramsar)
Sanderling, Calidris alba (4.2)
Teal, Annas crecca (4.2 and Ramsar)
Waterbird assemblage (4.2 and Ramsar)
Shelduck, Tadorna tadorna (4.2 and Ramsar) Portsmouth Harbour SPA/Ramsar
Shoveler, Anas clypeata (4.2)
Teal, Annas crecca (4.2)
Turnstone, Arenaria interpres (4.2)
Wigeon, Anas penelope (4.2)
Waterbird assemblage (4.2 and Ramsar)
Dark-bellied Brent Goose, Branta bernicla bernicla (4.2 and Ramsar)
Dunlin Calidris alpina alpina (4.2)
Black Tailed Godwit, Limosa limosa islandica (4.2)
Red Breasted Merganser, Mergus serrator (4.2)
Roosting and feeding sites in the Solent
During low water, waders and wildfowl feed on intertidal flats and as the tides rise they move to roosting or feeding sites located above the high water mark, usually in saltmarshes, fields or on beaches (Rehfisch et al, 1996). Previous work in the Solent was undertaken by the Solent Waders and Brent Goose Strategy 2010 (SWBGS) to identify the locations of designated and non-designated wader and wildfowl feeding and high-water roost sites. The broad findings of the SWBGS include:
• Intertidal habitats, including mudflats, shingle and saltmarsh provide vital feeding and roosting grounds for waders and wildfowl.
• Waders are specially adapted to feed in wetlands and feed and roost together sometimes in large numbers e.g. Dunlin
• Pattern of movement of waders is dependent on time of day, tidal water movements and weather conditions.
• Most species feed at low tide and roost at high tide.
• Natural roosting sites include saltmarsh areas, shingle banks and coastal grasslands as well as man-made structures such as boats, wharfs, jetties and piers.
• That a network of feeding and roost sites within and outside of designated sites may be important, not necessarily as just individual feeding and roost sites
• Natural roosting sites include saltmarsh areas, shingle banks and coastal grasslands as well as man-made structures such as boats, wharfs, jetties and piers
The SWBGS (Liley & Sharp, 2010) also undertook a characterisation study to try to understand what makes a ‘good’ wader roost or inland feeding area. The study identified that:
• Roosting sites tend to be close to the coast, with preferred sites averaging 500 m from MHW
• That roosts are usually situated away from sources of disturbance, such as housing and industry, and have good visibility
• For Brent Geese, their preferences for certain sites are not yet fully understood
• Roosting and feeding sites need to be in close proximity to conserve energy as required to build up energy reserves for migratory journeys and breeding
2.4. Development and disturbance pressure
The south of England has a number of densely populated urban areas and there are huge development pressures, particularly in south Hampshire. There are 1.7 million residential properties (equating to approximately 3 million residents) within 50 km of the Solent shoreline (Stillman et al., 2009). Substantial housebuilding is planned around the Solent to meet futur e housing needs and to support the sub-regional economy. The Solent is also a busy commercial, industrial and residential area.
Evidence shows that new development can reduce the habitat quality of the Solent SPAs, either by the loss of important nesting, roosting and feeding areas or via increased recreational activity along the coast as the result of population increases. There is therefore not only a considerable pressure on existing land, for both housing and associated infrastructure, but also for access and recreation. Furthermore, more housing and more people increases flood risk making FCERM schemes more necessary.
Over 1.4 million people live within a ten-minute drive of the Solent shoreline and it receives around 52 million visits each year. Visitors to the Solent coast travel relatively short distances: most less than six miles (Solent Disturbance and Mitigation Study, 2012). Dog walking is the most frequent activity, with walking, cycling and jogging also being common. The presence of people can result in disturbance to the birds, albeit often unintentional. Such disturbance reduces the opportunity to feed which can mean they have insufficient energy to survive or to complete migrations – potentially leading to a reduction in the bird population.
Many inland sites currently used by Brent Geese are also used for recreational, commercial, industrial or agricultural purposes, which on some occasions prevents or reduces usage by
Brent Geese due to disturbance. Several sites used by waders at high tide are also vulnerable to disturbance, especially from recreational activities, which would likewise prevent them from being used. Both waders and Brent Geese need a network of sites to choose from and fly between in order to cope with changing circumstances at individual sites.
Disturbance can have a variety of impacts, but all generally involve a reduction in the amount of energy that birds have available:
• Habitat that would otherwise be perfectly suitable and has a high density of food could be unused or underused.
• Birds could be forced to fly away from the source of the disturbance, using more energy as a result.
• Birds could be more alert when feeding, reducing their feeding efficiency over a given time period.
• There is a growing evidence base of non-directly observable effects on birds from human generated disturbance, which could lead to potential carry over effects into the breeding season (Inger et al., 2010).
The Solent Disturbance and Mitigation Project (Stillman et al, 2012) assessed whether the Solent SPAs bird populations are significantly adversely affected by recreational disturbance and what effect the addition of new residential development will have on this situation. This research concluded that current levels of recreational disturbance are having a significant impact and new residential development in the coastal zone will exacerbate this impact.
The density of the human population around the Solent and the current plans to further increase this, alongside the pressure to identify more green space for multi-functional usage and increased access to the coast in general, highlights the need to maintain a robust network of bird roosting and feeding sites in the Solent.
2.5. Coastal squeeze and sea level rise
The spatial distribution of coastal habitats is determined by tidal inundation. Changes in mean sea level shift the low and high-water marks, causing natural migration of habitat. Due to rising sea levels around the UK, this is predominantly occurring in the landward direction.
However, where manmade structures, such as sea walls or rock revetments, have been built to protect communities from coastal flood and erosion risks, habitat may be prevented from moving landward. This leads to habitat loss as the extent and functioning of the habitat reduces over time, a process called ‘coastal squeeze’.
In the Solent, a highly populated area, coastal squeeze occurs due to land being used for commercial, recreational and housing purposes which require defending. Saltmarshes are perhaps under the greatest threat from this effect.
2.2- diagram demonstrating coastal squeeze and role of manmade sea defences in intertidal habitat losses
Furthermore, coastal habitats also act as natural coastal defences, and their loss will lead to increased risk of flooding and coastal erosion as well as increasing pressure on man-made defences. If coastal squeeze causes a significant reduction in this protection then defences will need to be bigger and higher, and the cost of their construction and maintenance will rise as this happens.
Existing defences are often designed on the basis of a saltmarsh fronting them, in order to provide adequate protection from the effects associated with climate change and sea level rise (e.g. at Keyhaven and Lymington). If this habitat is lost, then the standard of protection will be reduced.
One of the most important issues in the future for the Solent’s coastal planners and managers will be how best to protect the coast for human use while allowing for the retention and movement of habitats as the sea level rises and wave conditions change. The Solent Bird Studies responds to this by creating an evidence base and decision-making tools for determining areas where habitat can be created.
Figure
2.6. Habitat creation/managed realignment
Following on from the previous chapter, there is an increasing need for habitat creation schemes principally through managed realignment to compensate for habitat losses due to coastal squeeze and sea level rise. The primary vehicle to deliver this compensation is the Environment Agency’s Habitat Compensation and Restoration Programme.
As many of the opportunities for habitat creation especially through the realignment of sea defences will affect landward habitats there is potential for a knock-on effect on overwintering bird use in these areas. This effect could arise from a change or loss of functional use of a site for birds, for example a reduction in roosting or feeding opportunities.
The potential effect on over-wintering birds from habitat creation is a significant issue for the delivery of these schemes and the FCERM schemes that rely on delivery of habitat compensation. The Solent Bird Studies responds to this by creating an evidence base and decision-making tools for determining areas where habitat can be created without loss of function use for over-wintering birds
2.7. Land management
Land management is a crucial factor in site suitability for waders and geese. Changes in land management regimes, or neglecting land management altogether, can reduce a site’s suitability. For example, grassland being poorly maintained or landscaping and tree planting around amenity sites can decrease visibility and thus reduce site suitability. Some crop types are unsuitable for waders and geese, as are ploughed fields and stubble. Furthermore, there are some sites where these birds are actively discouraged from feeding, for instance with gunfire or bird-scaring devices. Currently there are limited Agri-environmental scheme options to provide feeding or roosting habitats for brent geese or waders and are often restricted to particular geographic areas. However, there are options for creation/maintenance of habitat for wintering waders/wildfowl and supplements for winter bird food that could be adapted for the purpose.
2.8. Decision making
A short summary of the requirements relating to waterbirds in the relevant policy and legislation is given here, intended as an overview.
As described in Section 2.2, there is a detailed process by which a plan or project affecting an SPA/Ramsar or other designated site, including feeding or roosting grounds beyond the boundary of the designated site should be considered (Appendix C).
During Strategic Policy development, a Strategic Environmental Assessment (SEA), Water Framework Directive (WFD) assessment and HRA will be carried out. If required, an Imperative Reasons of Overriding Public Interest statement of case will also be completed as part of the HRA.
When the scheme reaches the preferred option scoping phase, an Environmental scoping report may be prepared and submitted to the Marine Management Organisation (MMO) and
Local Planning Authority (LPA). This will include a preliminary WFD assessment and initial information for the HRA.
Following further scheme development, during detailed design of the scheme, a full Environmental Impact Assessment (EIA) will be carried out, including a full WFD assessment, an Environmental Statement, full information for HRA (including AA and IROPI if required) and specific surveys carried out as advised by the scoping report, such as contaminated land and habitat surveys.
Applications will then be submitted to the MMO and LPA to seek approvals and licensing. Once these applications are validated and Planning Permission and Marine Licence with conditions granted, works will be undertaken to sign off the conditions in liaison with the contractor, such as development of a Construction and Environmental Management Plan (CEMP). Once the conditions are discharged by the MMO and LPA works can commence with ongoing environmental monitoring in compliance with the Environmental Mitigation Plan.
3. The Solent Bird Studies
3.1. Need for the Solent bird studies
• The requirement for this work was identified though the Solent Wide Network of Environmental Sites Scoping Study (2013)
• FCERM works are necessary along the Solent coastline to protect people. However, waterbirds are also protected in this area.
• Even for schemes that meet the requirements of the IROPI test, several assessments of a project’s environmental effects are legally required, and proposals for compensatory measures (e.g. habitat enhancement/creation) may be necessary.
• However, these effects are difficult to assess, given birds complex behaviour in using a multitude of sites.
• If it cannot be shown that either the population will not be negatively affected or that appropriate mitigation/compensation can take place then project cannot be approved.
• The Solent Bird Studies use a scientific approach to help this decision-making process, providing data-driven advice towards the best outcome for birds and people.
Due to the Solent’s importance as an over-wintering ground for a number of migratory bird species, which resulted in the designation of several protected areas, it has not always been possible to agree FCERM options at various locations along the Solent’s coastline. This has led to on-going debates about the future of sites and the adoption of ‘loose’ coastal policy that requires proposals to confirm the preferred future management of sites. However, more strategic medium- to long-term FCERM schemes are necessary in the Solent if coastal communities are to be protected from flood and erosion risks under future conditions. In order for these to be delivered on the ground, a greater understanding of how protected overwintering birds use the area, and a consistent, evidence-based approach is needed to advise these schemes.
The North Solent Shoreline Management Plan (2010) identified that further work was required to understand the impact of future coastal defence needs on internationally important bird populations. The subsequent Solent Wide Network of Environmental Sites Scoping Study (2013) investigated the current understanding and gaps in understanding. This study recognised that understanding both the importance of individual sites to birds and the connection between sites and related bird movements are of vital importance for ensuring we do not lose essential sites or break essential links, that could have a negative effect on the internationally important species we are legally obliged to protect. It is therefore essential that authorities are able to effectively assess the impact that schemes will have on bird populations, as well as identify and secure appropriate compensatory habitat. This is to ensure no net loss of roosting or feeding resources whilst maintaining the ecological coherence of the current network of statutory sites. The Solent Bird Study is aimed at addressing these concerns.
The Solent Bird Studies only consider the non-breeding bird populations for which the Solent SPA/Ramsar are classified. Therefore, only the over-wintering and to some extent passage migrant populations of waders and wildfowl, including the defined interest features and assemblage are considered. Other overwintering bird populations including passerines and seabirds, etc are not included within any analysis. Also, no consideration has been given to breeding seabird populations for which some of the SPA’s are also classified for.
The study area is defined as ‘The Solent’ and includes the open coastline and harbours from Millford-on-Sea to Pagham. It also includes the northern coastline of the Isle of Wight, from Totland running east to Bembridge.
In the Solent, previous survey attention has been paid to observing the sites used by birds in intertidal areas, through the Wetland Bird Survey (WeBS) counts, as well as ecologicallylinked inland sites, through the Solent Waders and Brent Goose Strategies (2002; 2010). These were able to identify currently important sites and the potential changes in the usage of sites by birds over time. However, at present we have a limited understanding of the ways in which wildfowl and wading birds move between these intertidal feeding areas and high tide roosting sites. The network and availability of suitable roosting and feeding sites is of critical importance for bird survival rates over winter and during their long migrations. The Bird Movement Study is therefore needed to improve our understanding of the way in which wildfowl and wading birds move around the Solent, particularly between intertidal feeding areas and high tide roosting and feeding sites.
This Solent bird study is needed to further develop prioritised activities and opportunities to deliver sites that can mitigate or compensate for high tide bird roosting and feeding sites within the Solent that will be impacted by coastal management decisions. Building on the work conducted by the Solent Waders and Brent Goose Strategies (2010), the study will enable decision makers to identify and preserve existing high tide bird roosting and feeding sites. These are areas whose loss is considered catastrophic to key bird species and the Solent as a wider network of environmentally linked sites. Furthermore, this study will identify key sites for the successful development of habitat for mitigation and/or compensation. The provision of this habitat is a legal requirement for sites that are likely to be lost over the medium to long term due to FCERM activities.
Overall, the Solent Bird Studies will enable decision makers to make better, more informed decisions regarding the development of future FCERM and habitat creation/compensation schemes along the Solent coastline. It will also confirm opportunities for the creation of new sites, where loss is unavoidable.
3.2. Aims and objectives
Coastal Network Study
The key aim of the Coastal Network Study is to develop prioritised activities and opportunities that can be undertaken by stakeholders within the Solent area to:
• Protect critically important high tide bird roosting and feeding sites;
• Confirm sites and techniques that have the potential to provide mitigation and compensation for high tide roosting and feeding sites; and
• Enable on-going delivery of FCERM schemes.
The key objectives to be met in order to achieve this aim are to:
1. Improve knowledge of high tide roost sites within the Solent that are critical to supporting roosting and feeding wildfowl and waders (integral links to a network of sites).
2. Agree mitigation and compensation options that maintain the Solent wide network of environmental sites for wildfowl and waders, enabling delivery of coastal change and FCERM schemes (i.e. if we lose current bird roosting sites to managed realignment, where can we create new bird roosting sites, with absolute confidence that they will effectively compensate / mitigate losses, and be acceptable to regulators and stakeholders);
3. Develop informed advice for future generation SMPs and FCERM strategies and confirmation of longer-term policy;
4. Develop informed advice for the delivery of the Regional Habitat Compensation Programme (RHCP) and FCERM schemes, which improve the environment and protect our communities. The RHCP is the Government's approved strategic compensation mechanism for addressing habitat losses arising from FCERM;
5. Create a spatial tool for education, engagement and decision making;
6. Develop a strategy for the protection of key sites via Local Authority Local Plans and informed advice towards future development that could bring significant contributions towards match funding Flood Defence Grant in Aid (FDGiA).
7. Produce a comprehensive final written report for presentation and justification of outputs within the spatial tool.
Bird Movement Study
The key aim of the Bird Movement Study is to understand and maintain or enhance the network of environmental sites within the Solent, and the links between them, whilst protecting our communities from coastal flood and erosion risks.
The key objectives to be met in order to achieve this aim are to:
1. Baseline our current understanding of bird movements within the Solent and improve our knowledge of links between feeding and roost sites for different bird species.
2. Establish additional data requirements to develop and confirm our current understanding of bird movements within the Solent. This is achieved via communications with stakeholders including environmental regulators, operating authorities and decision makers to ensure the correct level of data is collected in order to allow coastal change FCERM decisions to be made.
3. Implement measures for capturing this information through the development of guidance and new data collection techniques.
4. Discuss with regulators, operating authorities and decision makers and agree on a scientific basis across the Solent that will enable delivery of future FCERM, through decisions that maintain the Natura 2000 network of sites while allowing schemes to be delivered on the ground.
5. To develop a spatial tool for engagement and decision making by creating a GIS database.
4. Determining Relative Site importance
As described in Section 2.1, the project has largely determined that the elements of the 2 projects are largely interlinked and therefore the findings have been delivered as one report. However, for certain aspects it is logical to describe the approach to the two elements separately. The following is a summary of the work that was undertaken to determine the relative importance of an individual roost site within the network.
4.1. Analysis of WeBS data
To establish a knowledge baseline for waterbird distributions in the Solent, data from the British Trust for Ornithology’s Wetland Bird Survey (WeBS) were analysed. These data were analysed in order to:
• Assess the size of waterbird populations in the Solent as a whole and compare them with thresholds for national and international importance.
• Compare low- and high-tide counts for each estuary, in order to look for evidence of movements between estuaries during the tidal cycle, and examine the role of coastal development and population pressure.
• Investigate whether existing data is appropriate for assessing distributions of species that use inland fields outside of the SPA network.
Data on species field usage were extracted from each species’ entry on the IUCN Red List of Threatened Species (BirdLife International, 2017).
Data collection
In WeBS ‘core counts’, distributions of birds at high tide, when many are roosting, are recorded monthly. Low-tide counts, when birds are feeding, are conducted monthly during the winter at approximately five-yearly intervals (Frost et al., 2017). The dates of low-tide counts used in this study are shown in Table 4.1
Table 4.1: Years in which low-tide counts were conducted in each surveyed section of the Solent. For example, the Beaulieu estuary was counted monthly from September 2010 to March 2011.
Sector Winter beginning
Beaulieu Estuary 2010
Bembridge Harbour 2010
Chichester Harbour 2010
Langstone Harbour 2009
Newtown Harbour 2008
North-west Solent 2012
Portsmouth Harbour 2008
Southampton Water 2000
The surveys focus on estuarine areas and adjacent terrestrial habitats, which are subdivided into sectors that are surveyed by separate recorders (Figure 4.1). All birds encountered are recorded. For these analyses we excluded seabirds such as gulls, terns, divers, grebes and shags, in order to follow the definition of ‘waterbirds given by the JNCC in the second SPA review (Stroud et al., 2001).
We calculated mean and peak numbers of birds, both for the total waterbird assemblage and restricting analysis to particular species of interest. Peak numbers of species in the Solent as a whole were compared to the thresholds reported by the BTO (Frost et al., 2017) to assess the species for which the Solent holds nationally or internationally important populations.
Solent waterbird population sizes
Overall, within the Solent, populations of 25 species were assessed as nationally important, and nine were internationally important. The average peak waterbird population in the Solent was 132,616, which is comparable to the North Norfolk Coast (Frost et al., 2017).
Figure 4.1 Areas covered by the WeBS high tide (left) and low tide (right) counts (data courtesy BTO)
Table 4.2 Waterbird populations in the Solent assessed by BTO WeBS high tide counts. Species whose annual peak population in the Solent exceeds the threshold for national importance are indicated by * and species whose populations exceed the threshold for international importance are indicated by **.
Comparison between high and low tide: Estuaries
In general, more birds were counted in each estuary at low tide than at high tide (Figure 4.2). In particular, Portsmouth Harbour and Southampton Water had notably fewer birds at high tide than predicted from low tide counts (2,500 and 3,500 fewer birds respectively; Table 4.3). The north-west Solent was the only area with significantly more birds recorded at high tide, with observed counts exceeding predictions by 3,700.
Table 4.3 Observed median Low and High Tide Counts (LTC and HTC respectively) from Solent estuaries, with the predicted high tide count from a regression model, 95% confidence intervals for that prediction, and the difference between the predicted and observed high tide counts. Cases where the observed count deviated significantly from the model are highlighted in boldface.
This may reflect birds moving between estuaries during the tide cycle. The harbours losing birds tend to be the most urbanised, while the north-west Solent is comparatively undisturbed. Numbers lost and gained at high tide often match between neighbouring estuaries, for instance Langstone and Chichester Harbours, or Southampton Water and North-west Solent. Therefore, while areas like Portsmouth Harbour may represent rich feeding opportunities, the lack of sites for roosting – due to coastal squeeze and disturbance – limit the number of birds that can persist there throughout the tide. This is an observation that has been made repeatedly during the history of development in the Solent (Pratt and Glue, 1968; Tubbs, 1990; Unsworth, 1994).
Overall, there was a close correspondence between numbers of birds at low and high tide, with low-tide count totals explaining 93% of the variation in high-tide counts. Figure 4.2 shows the result of the linear regression (F1,6 = 78, p < 0.001).
Figure 4.2: The total waterbird assemblage at low and high tide in each estuary is linearly related. The dotted line shows the relationship y=x, which would be observed if numbers were equal between counts. The blue lines show a linear regression with 95% confidence intervals. Abbreviations: BE=Beaulieu Estuary; BH=Bembridge Harbour; CH=Chichester Harbour; LH=Langstone Harbour; NH=Newtown Harbour; NS=Northwest Solent; PH=Portsmouth Harbour; SW=Southampton Water.
Comparison between high and low tide: Bird species
We used the proportion of individuals of each species that were recorded at high tide as a measure of tidal recording bias: if a species was recorded equally at high and low tide, the proportion would be 0.5. Scores over or under 0.5 indicate that more individuals were recorded at high or low tide respectively.
Data on bird species use of terrestrial fields for foraging or roosting (Table 4.4) were collated from species accounts in the IUCN Red List of Threatened Species (BirdLife International, 2017). Birds that feed in fields tend to be recorded more frequently at high tide than at low tide (Figure 4.3). For species that use offshore habitats only, there was no systematic trend, though most species tended to be recorded more at low tide.
Table 4.4 Use of inland fields for foraging or roosting by waterbirds
Use fields No field use
Bewick's Swan Avocet
Black-tailed Godwit Bar-tailed Godwit
Brent Goose (Dark-bellied) Gadwall
Common Sandpiper Green Sandpiper
Coot Greenshank
Curlew Grey Plover
Curlew Sandpiper Knot
Dunlin Little Ringed Plover
Golden Plover Little Stint
Jack Snipe Purple Sandpiper
Lapwing Redshank
Mallard Sanderling
Moorhen Shelduck
Mute Swan Shoveler
Oystercatcher Turnstone
Pintail
Ringed Plover
Ruff
Snipe
Spotted Redshank
Teal
Water Rail
Whimbrel
Wigeon
Wood Sandpiper
Woodcock
As high-tide surveys generally achieve better coverage of inland areas than low-tide counts, it is likely that field-using birds are undercounted during the low-tide counts. Of the species
recorded more at low tide, these tend to be small species that roost in dense flocks, such as Dunlin (a field-user, though typically recorded offshore in the Solent), Sanderling and Knot (offshore-only). Low-tide counts of the sparser feeding flocks are probably more likely to be accurate, while attempts to count dense roosts at high tide likely result in underestimates.
Discussion
These results strongly indicate that waders avoid roosting in estuaries that lack suitable roosting sites or where disturbance is too high. In turn, this may suggest that some areas are under-utilised by birds at low tide due to a lack of suitable roosting sites nearby (Dias et al., 2006; Rogers et al., 2006a). Artificial roost sites and refuges that have lower levels of disturbance have repeatedly been shown to be well-used by waders (e.g. Burton et al., 1996; Kitchen and Young, 2007; Farrell et al., 2016).
These results also indicate that knowledge of the feeding distributions of field-using birds may be incomplete, as these birds’ locations at low-tide are under-recorded. Furthermore, the importance of roost-sites for small wader species (in particular Calidris spp.) may well be under-estimated, as counts of widely-dispersed feeding flocks (at low-tide) are less likely to under-record total numbers than attempts at estimating the sizes of flocks of densely-packed roosting birds. It is also likely that offshore roosts, for example on islands, may be missed due to the difficulty of detecting small grey waders amongst saltmarsh vegetation at long range.
Figure 4.3: The proportion of records of individuals recorded at high tide is higher for species that use inland fields. Each dot is the value for an individual species; boxplots show the median (thick line), and IQR (box) of data.
Recommendations
Existing roost sites should be protected wherever possible, and opportunities to enhance or create roost-sites in the more developed estuaries, in particular Portsmouth Harbour and Southampton Water, should be explored. Given the difficulty in accurately counting several species, even roost-sites believed to be used by small numbers of birds should be treated cautiously.
Further work is needed to map the foraging sites used by field-using birds in particular, especially as many of the sites used fall outside the current SPA network, although these sites should be protected as functionally linked land, there is sometimes insufficient evidence to support their protection as it is not ‘automatic’ as it is inside SPA (Rowell and Robinson, 2004; Stroud et al., 2016).
4.2. Understanding relative site importance
The purpose of data collection for the Coastal Network Study was to determine the relative importance of individual wader roosts and inland fields used by waders and/or Brent Geese. Due to the widespread nature of the study area it was determined that a citizen science-based approach would be utilised; to survey an area of this size with professional surveyors would have been prohibitively expensive. To enable this approach and also help to ensure consistency of data a bespoke smartphone application (SolentBirds for iOS and Android) and an online recording website (www.solentbirds.org.uk) were developed for the project.
The methodology promoted was similar to previous studies including the Solent Waders and Brent Goose Strategy (2010) and Chichester Harbour Goose Watch (2007-2011). Volunteers were asked to cover a ‘patch’ on a regular basis ideally fortnightly, although ad-hoc records were also accepted. All observers were asked to focus surveys in the period two hours either side of high tide, although records were accepted for inland field use, where use is less tidally influenced. The ‘look-see’ (Bibby et al., 2000) method was used, with observers recording the numbers and locations of waders, wildfowl and seabirds to species level, alongside a number of other metrics: date, time, habitat, behaviour, disturbance and bird scaring devices. In addition to recording the presence of birds, the absence of birds using a site was also recorded. All records were submitted through the app or website, which both recorded the same information and records were stored in a common database.
Geographical coverage was monitored throughout the survey and attempts were made to fill gaps, including seeking volunteers in these areas and also in some circumstances using paid surveyors.
There is often a concern regarding the quality of citizen science-based recorders. Although no training was provided for observers, potential observers were quizzed on their birding experience, were asked to make a self-assessment of their skill level and project staff were able to rapidly respond to queries from observers on methodology and species identification matters. Furthermore, and most significantly, the online recording system (both app and website) contained a verification stage, wherein all records were assessed by a suitably qualified and experienced ornithologist. Records were accepted, rejected or queried based upon the expert judgement of the verifier.
Methodology
A range of survey techniques were used to collect bespoke data, and a range of the data was collated from other sources to support the analysis. This process is described in the following sections.
4.2.1.1.
Structured surveys
Structured surveys following a defined protocol are the gold standard in ecological recording. Standardised waterbird counts for the Bird Movement Study followed the Vantage Point method described in Section 5, and also contributed data to the Coastal Network Study (CNS).
However, these surveys are financially expensive; even when volunteers are used, they require a lot of organisation and data-entry. Due to the expense, it was not feasible to cover all sites in the Solent network through standardised means.
Surveys were organised by the Coastal Partners using three paid surveyors, who contributed around 1,500 records (exact total unavailable as some records were submitted through the app). Additional surveys were organised by the HIWWT using a mixture of 25+ paid and volunteer surveyors, who contributed 2,216 records that were used in the CNS.
4.2.1.2.
SolentBirds app
Citizen Science is a burgeoning approach to data-collection in ecology, that combines research with public engagement (Pocock et al., 2017). The coast of the Solent is a very popular destination for recreational birdwatching, and so, by providing a simple interface, the SolentBirds app (Figure 4.4) enables mass participation in the process of providing field-scale data on bird numbers.
Figure 4.4 Entering a bird record using the SolentBirds mobile app
Users select a location by clicking on a map, and then can record numbers observed from a list of species of interest. Optionally, information about birds’ behaviour, disturbance and habitat type can be included. Users can also enter negative records – that a site was visited but no birds were seen – although few do so. However, the inclusion of gulls on the species list leads to the submission of records where a site was visited and had no waterbirds, which were included as negative records in the CNS.
At the time of this study, over 17,000 records had been submitted to the SolentBirds database through the website http://solentbirds.org.uk or via the smartphone app. Together with its precursor scheme, the now-defunct GooseWatch, these records comprised the vast majority (82%) of records used in this study. Based on the Heritage Lottery Funds valuation (undertaken to 2021 values) of skilled volunteer time (£150 per day), SolentBirds records represent an in-kind contribution of £224,850
Ensuring data quality, with accurate identifications and locations, is a challenge for users of citizen science data (August et al., 2015). In SolentBirds, every record is verified by approved personnel, and recorders are contacted to clarify any improbable records. The app also allows the submission of photos to support records.
The data is available for anybody to download and is also shared with county recorders and records centres. As there is a need for up-to-date information about a large number of sites around the Solent, continued investment in the app would be beneficial by providing this data at a relatively low cost. Furthermore, there are plans to enhance the app in two ways to increase its usefulness to studies of this nature:
1. the addition of an optional map overlay depicting sites of interest, based on the Solent Wader and Brent Goose Strategy sites
2. adding functionality to input bird movement records, enabling citizen science to contribute to future bird movement studies as well as coastal network studies.
3. Highlighting under recorded/data deficient sites that would benefit from additional recording to better understand their status
These enhancements will allow the app to be used as a standardised data entry portal and data repository for future surveys, eliminating the previous problem of variable data archiving practices.
4.2.1.3.
WeBS
The BTOs Wetland Bird Survey (WeBS) is conducted monthly, year-round, at high tide. In addition, every 5 years monthly low-tide counts are undertaken during the winter (Frost et al., 2017). These surveys provide the best available evidence on population sizes and trends of waterbirds in the UK.
However, the spatial scale at which the counts are conducted is too broad to be directly incorporated into these studies, as each sector covers multiple onshore and offshore sites. Therefore, while WeBS data was used to assess the local value of a site, relative to the adjacent sectors populations of each species, counts from WeBS surveys could not be included in our analyses.
On the other hand, the WeBS surveys mobilises a large number of skilled volunteers every month, many of whom count waterbirds using terrestrial sites such as fields; if they can be encouraged to submit this data via the app their records would be a boon to the Solent Bird Studies.
The Wetland Bird Survey (WeBS) is run by the British Trust for Ornithology (BTO). It is a partnership between the BTO, the Royal Society for the Protection of Birds (RSPB) and the Joint Nature Conservation Committee (JNCC) (the last on behalf of the statutory nature conservation bodies: Natural England (NE), Natural Resources Wales (NRW) and Scottish Natural Heritage (SNH) and the Department of Agriculture, Environment and Rural Affairs, Northern Ireland (DAERA)) in association with the Wildfowl and Wetlands Trust. (WWT).
4.2.1.4. eBird
eBird is the largest ornithology citizen-science project in the world, allowing users to record birds anywhere globally (Sullivan et al., 2009). As with SolentBirds, users enter a location and a list of birds seen there, and data can be downloaded free of charge by anybody.
However, after a preliminary investigation of using this data for the CNS, we found that the point entered was often the centre of a far wider area; for instance, records from the whole of Farlington Marshes and offshore may be entered as having occurred at a single point in the middle of a scrubby field where in fact few waterbirds occur! While users can enter the distance they covered, only 55% of records analysed had this information. Where effort was recorded, the median distance covered was 3 km – far greater than the scale of most sites of interest for the present project.
This greatly reduces the usefulness of this data for site-based analyses, as one can’t be sure that the records refer to the particular site of interest.
4.2.1.5. BirdTrack
Similar to eBird, BirdTrack is a citizen-science portal developed by the BTO, and is more widely used among UK birders. Data requests cost £50, and given the limited use of eBird data the exercise was not repeated with an additional dataset. Unlike eBird, users can enter sites as OS grid squares, polygons or transects as well as points; however, these spatial units rarely align with the target sites for the CNS. Therefore, for our purposes, a dedicated citizenscience portal is the only one providing data that can be integrated with historical data, and data from other sources, at an appropriate scale for making planning decisions.
4.2.1.6.
Datasets utilised
The following datasets are those used within the analysis for the coastal network study representing records of visits to individual sites, this included;
• birds_sites_merged_230614: a collated dataset of positive and negative sightings, including data from the historic records from Chichester Harbour Conservancy, Chichester Harbour Goosewatch, Solent WaderWatch and HCC Ecology Team/HBIC surveys for Local Authorities.
• SW&BG records 2016: previous records from the Hampshire and Isle of Wight Wildlife Trust (HIWWT) including records from the Solent Waders and Brent Goose Strategy, RSPB and Betts Ecology Report.
• Solent Birds Studies (SBS): all records up to 21st July 2017 from the website and app collected as part of this project.
• Snapshot counts: An element of the first methodology trialled for the joint SWBGS/SBS vantage point surveys undertaken by SBS and SWBGS surveyors in winter 2016-17. The data represents mapped surveys of the location of birds at hourly intervals during the survey period.
• Movement records: bird movements were recorded during the vantage point surveys, undertaken in the winter 2016-17, including the combined SBS/SWBGS surveys, the separate SBS surveys and SWBGS surveys. Where an origin or destination was confirmed, this was treated as a record of those birds at that location.
These data were all formatted to a consistent standard, obvious errors removed and then collated into a single dataset.
4.2.1.7. Data filtering
Records from outside the survey period (October-March inclusive) were excluded. Only records of certain species were included. For the HIWWT analyses, these are Brent Geese and waders; for the ESCP analyses, all waterbirds (as defined by JNCC; Stroud et al., 2001 as used to establish waterbird assemblage statistics for SPA) are included. Visits where only non-target species were recorded were still used to calculate the number of visits to a particular site, but otherwise records of non-target species are excluded from analysis.
Data analysis: Records
Each record is spatially linked via associated Easting & Northing coordinates. Each record’s ‘importance’ was assessed in the following ways:
• Comparison to population thresholds: the BTO publishes national and international thresholds for each species, after which a count of that species should be considered of critical importance.
• Comparison to SPA qualifying features: if the record is of a species classified as a ‘qualifying feature’ in the closest SPA, the number of birds recorded is compared to the qualifying population size listed in the SPA classification. If the count is at least 1% it is considered part of the auxiliary network, and if it is 5% or more it is considered a critical network site.
• Comparison to SPA waterbird assemblage: for SPAs where the total waterbird assemblage (the ensemble of all species occurring in the SPA) is designated as a qualifying feature, the total number of birds recorded on a single visit was compared to the assemblage size listed in the SPA classification. Unique visits to a site are identified by the combination of recorder, date and location. The total number of birds (of all included species) recorded during that visit is calculated by summing the maximum count of each recorded species. If the count is at least 1% of the classification population the site is considered part of the auxiliary network, and if it is 5% or more it is considered a critical network site.
• Comparison to median WeBS counts: each record is compared to the median total of that species from the closest WeBS high-tide counts from the years 2008-2013; if the record exceeds the median then it is considered at least auxiliary network.
These spatially-linked records with their importance information appended can then be compared to any other GIS data, for example the SWBGS sites for comparative analysis.
Data analysis: Network characteristics
Using data from the movement surveys (see Chapter 5), the network of sites used by Brent Geese and waders was mapped. All movements where both the origin and destination were observed by the surveyor were included.
The properties of this network were then analysed in order to identify two types of sites: those that function as ‘hubs’, with connections to lots of other sites, and those that function as
‘bridges’, linking two regions of the network together. These are identified using the following metrics:
• hubs are identified by their degree: this is simply the number of other sites to which they are connected
• bridges are identified by their betweenness centrality: this is (roughly) a measure of the number of pathways through the network that pass-through a given site
Note that some sites may score highly on both metrics, functioning essentially as both a hub and a bridge.
The network analyses were conducted using the igraph software package (Csardi and Nepusz, 2006).
Data analysis: Site importance
The analysis included all records that occurred within a site of interest. Each record was individually compared to the thresholds listed above (Sections 4.2.3 and 4.2.4). Any site containing a record that exceeded any one of the thresholds was considered part of the coastal network.
Sites’ betweenness centrality and degree scores also indicated whether sites were an important part of the network. If degree exceeded 4, or betweenness centrality exceeded 1, the site is considered a Critical network component. Site that exceeded other thresholds but did not appear to important as a bridge or a hub were classified as auxiliary sites.
Sites which were not considered part of the critical or auxiliary network were classified as ‘potential’, indicating that the site is not frequently used by a statutorily important number of birds. However, potential sites with fewer than 5 unique visits within 2.5 hours of high tide were reclassified as ‘data deficient’. Counts close to high tide are desirable as they are more likely to reflect peak use, due to birds tendency to feed offshore at low water. Five visits were deemed an acceptable minimum number as bird numbers fluctuate a lot depending on disturbance, weather conditions and other influences. Site where under 5 visits were undertaken were considered data deficient.
4.3. Coastal Network Study results
Out of 1,312 terrestrial sites included in the analysis, there was enough data for 656 (50%) of them to assess their importance (Table 4.5). Of these, 475 (72%) were found to be important to the coastal network of waterbird sites (as critical or auxiliary network sites) See Appendix A for a series of maps illustrating the results.
Figure 4.5- overview map of Solent Bird Studies results, see Appendix A for a series of higher resolution maps
Table 4.5: The number of assessed sites falling into each category
Some importance thresholds were crossed by more sites than others, with the SPA classification-based criteria proving the most exclusive, and the WeBS-based threshold the most commonly exceeded (Table 4.6). These are appropriate results, as the SPA network is designed to conserve sites of international importance, whereas the WeBS data was included specifically to identify sites of local importance only.
Table 4.6: The number of sites scoring in each category for each of the variables used to assess site importance. Note that row totals do not match those in Table 4.5, as a site may score highly in multiple categories. n=1,312 sites.
Of the 30 sites considered important due to the Bird Movement Study network analysis (Table 4.6), only 15 (50%) were identified as important using the traditional thresholds based on comparing counts of static flocks to the SPA designations. Furthermore, while a detailed habitat analysis has not been undertaken, these 30 ‘Important-Movement’ sites include many with highly modified land-used, such as agriculture or sports/recreation, which are typically not classified as SPAs or notified as SSSIs (Table 4.7).
Table 4.7: The habitat types of sites identified as Critical Network sites by the network-analysis approach taken in our Bird Movement Study (section 3.2.4), the number of sites that would have been equivalently rated by the traditional, count-based approach using the SPA classifications (section 3.2.3), and the number of sites included in existing protected areas.
4.4.
Site characterisation
Previous research
An earlier analysis compared characteristics of sites that were important for waders and Brent Geese, versus sites with less or no recorded use (Liley and Sharp, 2010). Overall, birds prefer large, flat, low-lying sites close to the coast. Important sites also tended to be coastal or grassland habitats, while habitats such as woodland were avoided.
Waders in particular favoured sites far from buildings, and waders were also affected by the number of addresses registered in the vicinity (this metric presumably functions as a proxy for local population density, and therefore frequency of recreational disturbance).
There was also an influence of site isolation, i.e. the distance to other used sites. Brent Geese select sites close to other areas used by the species; conversely, however, important wader sites tended to be isolated from other sites. This may reflect differences in how the two groups of birds use inland sites: Brent Geese forage in a feeding circuit, and selecting neighbouring sites reduces energy expenditure in travel. On the other hand, waders are using the sites for roosting, preferentially in large numbers, so a few sites will tend to concentrate many individuals as feeding habitat is covered by the rising tide.
This study did not attempt to reproduce these results, which are considered a robust baseline for understanding how site characteristics influence their importance to birds, and provide criteria that can be used for selecting and managing new sites to act as reserves or compensation.
Comparison with current data
Liley and Sharp (2010) also presented a number of sites that, according to their analysis of site characteristics, were similar to important sites for waders and/or Brent Geese, but were contemporaneously classified as low use sites, under the Solent Waders and Brent Goose classification. They were therefore considered to be sites with high potential for future use.
All of these future potential sites identified by Liley and Sharp (2010) were included in the Solent Birds Studies, and therefore their importance for waterbirds was classified in the current Coastal Network Study analysis. The number falling into each category is presented in Table 4.8.
Table 4.8 Number of sites that overlap with the SWBGS 2010 ‘future potential sites'
Due to slight variations in the size, shape and position of the polygons from each database, some of these future sites not only overlap with their corresponding SBS site, but also adjacent sites. However, it is still possible to see that a significant number of overlapping sites are data deficient so require further study to determine their importance for waders and wildfowl.
Future research
Particularly with a view to informing future site management, it would be valuable to extend these analyses, using the natural experiment of changing land-uses over time. Anecdotally, the extent to which Brent Geese and waders use certain fields varies between years, as does the management of that site – a particularly important example is the crop type and timing on
agricultural land: a field may be important one year when planted with cereals, but unused the next if left as stubble, or planted with potatoes.
A historical analysis of annual peak counts from well-recorded fields could use freely-available remote-sensing data (Kerr and Otrovsky, 2003). Previous studies have developed methods to characterise vegetation characteristics such as crop type (Blaes, Vanhalle and Defourny, 2005) and phenology (Sakamoto et al., 2005), which could be applied to fields of varying importance to geese and waders. By comparing the same fields over time, other factors such as geography (e.g. distance from coast, area, topography) are held constant, so the land management can be studied in isolation. This would inform managers how best to manage a given site to promote use by the target group.
4.5. Vulnerable sites
Future coastal defence and habitat creation projects
The so called ‘Asterisk sites’ are those identified with the North Solent Shoreline Management Plan (2010) as a site with a current policy for Hold the Line, but which should be investigated for their potential for undertaking habitat creation projects.
We analysed existing bird data for the Asterisk sites. This analysis used the same methods as the Coastal Network Study but focussed on the areas of Habitat Creation Opportunities rather than the polygons of Coastal Network Study sites.
Almost 40% of sites were Data Deficient, with no bird records from within their area. Of the 35 sites that had records, over half were categorised as Critical Network, and most of the rest were in the Auxiliary Network, with only two sites (3.5%) categorised as Potential (Table 4.9).
Table 4.9 Categories of each Habitat Creation Opportunity / Asterisk site around the Solent, following the Coastal Network Study methods. Also included are whether or not a record of any waterbird species crossed the threshold for national importance in Great Britain; whether any species crossed 1% or 5% of its designated level as an SPA feature of interested; whether any site was an important ‘hub’ or ‘bridge’ in the Bird Movement Study (BMS); and the number of qualifying visits to that site during the study period.
Most of the Data Deficient sites are from the western portion of the Solent, however. In the better-recorded East Solent harbours, it was possible to assign ecological importance levels to most sites. Most of the larger habitat creation opportunities are already classified as being part of the Critical Network (Figure 4.6).
Figure 4.6 Classifications of the ecological importance of East Solent asterisk sites.
However, these results should be considered preliminary only. In many cases, the proposed habitat creation area encompasses a large area, of which only a small portion may host important numbers of birds, with the remainder of the site representing a golden opportunity to create new habitat adjacent to an area already known to be used by birds.
Each individual habitat creation scheme would therefore benefit from detailed surveys of both habitat and how birds are using the site, in order to ensure that existing ecological functions are preserved or enhanced alongside new habitat creation development.
Planning and development
There is considerable pressure for land within the Solent, with competing influences including residential development, commercial development, recreational activities and wildlife. The analysis below is an attempt to assess the degree of conflict between sites planned for development and sites’ importance for over-wintering waders and wildfowl.
4.5.2.1.
Methods
Data for planned development allocations within current or developing Locals Plans was collated from Eastleigh Borough Council, Chichester District Council, Fareham Borough Council, Gosport Borough Council, Havant Borough Council, Isle of Wight Council, New Forest District Council, Portsmouth City Council, Southampton City Council, Test Valley District Council and Winchester City Council. Allocation sites were compared with results from the Coastal Network Study to see how many important sites overlapped with planned developments.
Table 4.10 Types of planning allocation obtained from each authority (data from 2019)
1no data available to this study
2data not separated into e.g.
3only employment allocations given
4.5.2.2.
Results
A total of 88 sites could be lost or negatively impacted due to current planning proposals, and 8% of all overlapping sites are classified as of critical importance for waders and wildfowl. A further 42 sites at risk of development have been identified as data deficient (Table 4.11). Boroughs differ in number of affected sites: for example, the total includes 34 sites in Gosport,
whereas there were no overlapping sites in the Chichester district or on the Isle of Wight (Table 4.12-Table 4.14).
Table 4.11 Number of sites that overlap with areas planned for development
Table 4.12 Number of sites within each borough that overlap with areas planned for housing
Table 4.13 Number of sites within each borough that overlap with mixed development
Table 4.14 Number of sites within each borough that overlap with areas planned for employment
It is possible that additional sites are also at risk from development as there was no data provided by two boroughs (Eastleigh and Test Valley), while other areas (such as the Isle of Wight) only provided data for business development.
4.5.2.3. Discussion
The loss of important sites to development would likely have a varying impact on wildfowl and waders as dependent on the ecological function(s) provided by each site, and the availability of suitable sites nearby to accommodate the displaced birds. Other sites would not be lost entirely due to current planning allocations as some sites were found to only partially overlap with a development.
However, even sites only partially lost to development would likely suffer from increased disturbance levels, especially if the overlapping development included residential properties. Furthermore, sites currently classified as potential may increase in importance if birds that originally relied on sites found to be of greater importance were displaced by a development. Indeed, potential sites are used less relative to critical or auxiliary sites, so are likely to still be important for birds.
Many sites earmarked for development are currently data deficient. This is concerning as there is a chance such sites could be lost before their importance for waders and wildfowl is known which could have a detrimental impact on the local populations. It is possible some of these sites could be actively improved and managed for birds with appropriate monitoring, could turn out to be critical or auxiliary sites that have previously been overlooked.
5. Understanding Bird Movement and the Network of Sites
As previously described, the two originally envisaged aspects of the overall Solent Bird Studies, the two parts the coastal network study and the bird movement study were found to be inextricably linked and an understanding of both is required to answer the questions posed by the study. However, for certain aspects it is logical to describe the approach to the two elements separately. The following is a summary of the work that was undertaken to
study movement of birds and determine the relative importance of the network of sites, previously within the Bird Movement Study work area.
5.1. Understanding Bird Movement
To estimate the impact of losing a roost site on a population of waterbirds, it is necessary to consider how far birds from that population will travel to foraging areas or alternative roost sites (Dias et al., 2006; Conklin and Colwell, 2007). Methods traditionally used to assess this catchment area include plumage dying (Norton and Demopoulos, 2000; Dias et al., 2006), colour-ringing (Symonds et al., 1984), radio-tracking (Conklin and Colwell, 2007), and more recently-developed hi-tech methods such as Global Navigation Satellite System (GNSS) data loggers (López-López, 2016).
However, each of these methods requires fieldwork in two stages: capturing birds, and subsequently tracking them. Capturing birds is generally time-consuming, despite which it is difficult to ensure that the desired sample sizes are obtained (Norton and Demopoulos, 2000). Furthermore, it is a skilled endeavour requiring years of training and specific licensing (Redfern and Clark, 2001), as well as landowners’ permissions to access sites. Finally, equipment for catching large numbers of waders through cannon-netting is very expensive, totalling thousands of pounds, as are devices for tracking individual birds.
Given the large investments of time and money required, as well as the scarcity of suitably qualified personnel, it may sometimes be desired to assess bird movement patterns without undertaking a bird-marking project. To this end, we designed a movement survey method, hereafter referred to as vantage-point surveys, and trialled them to test their suitability for gathering bird movement data at a strategic level.
Field methods
In principle, the method is simple. Survey organisers identified a set of suitable vantage points from which a broad area used by birds can be seen. Surveyors were then stationed at each vantage point around high-tide and recorded the species identity and size of all waterbird flocks seen moving, and, wherever possible, the origin and/or destination of that flock.
By conducting the surveys simultaneously, multiple surveyors provide results that can potentially be interpreted as an ensemble, enabling the survey organisers to track a flock’s movement past multiple surveyors in sequence.
The methodology was tested with a series of trial surveys undertaken in 2015/16 at Hook Lake, Farlington Marsh and Conigar Point, which provided a proof of concept. In 2016/17, in collaboration with the Solent Waders and Brent Goose Strategy Steering Group (SWGBGSG), a large team of observers (19 vantage points and 2 roving observers) were placed covering Chichester, Langstone and Portsmouth Harbours. The results were disappointing; observers were too widely spaced to enable full coverage, very few large-scale movements were observed, a large number of observers records were inconsistent, and it was very difficult recruiting a team to assist with the surveys leaving many gaps It was also a logistical nightmare attempting to organise 21 observers to survey at the same time. This approach was therefore halted before a second survey was commenced and SWBGSSG and Solent Birds undertook separate approaches to understanding bird movement reflecting the differing purposes of the two projects.
The vantage point surveys for the Solent Bird Studies undertaken in 2016/17 involved using observers covering a manageable area in which we could record a dense and robust dataset. Langstone Harbour was chosen due to its accessibility, general good inter-visibility and known good bird population. It was determined that 3 observers could provide good coverage of the entire harbour. From October to March surveys were undertaken twice monthly over a rising tide period, 4 hours before high tide to high tide. Which equates to 12 surveys, with 48 hours of observations per station and 144 hours of observations in total.
The SWBGSSG adopted a roving observer methodology using small teams, principally focusing on inland feeding brent goose flocks. Tracking and locating flighting geese and then monitoring movements to and from feeding areas.
Where either of these methods identified movement and particularly where observations included an origin and destination the data has been used within the analysis, and vice versa Solent Bird Studies data has been used within the analysis of the Solent and Waders and Brent Goose Strategy 2018.
Analytical methods
Initially the results were used to create two maps, one showing all movements, even those where at least one terminus (startpoint or endpoint) was unobserved, and another including only fully observed movements where both the start and endpoints were identified. However, the resultant spider-web was not very enlightening, as it was difficult to detect patterns with so many paths overlain. We therefore developed a method that would enable us to identify areas of particular importance.
Each movement with both a confirmed origin and a confirmed destination was included in the analysis. Each movement connected two sites together. Where a movement involved a site that was already linked to another by a previous movement, the total network grew:
Figure 5.1-visual representation of recording/growing networks from survey observations with both termini observed e.g. with an origin and destination recorded.
This ultimately led to a network diagram including all sites to/from which movements had been recorded.
We then used the software package igraph (Csardi and Nepusz, 2006) for R (R Core Team, 2016) to calculate two properties of this network, which were then analysed in order to identify two types of sites: those that function as ‘hubs’, with connections to lots of other sites, and
those that function as ‘bridges’, linking two regions of the network together. These are identified using the following metrics:
• hubs are identified by their degree: this is simply the number of other sites to which they are connected; and
• bridges are identified by their betweenness centrality: this is (roughly) a measure of the number of pathways through the network that pass-through a given site.
5.2. Bird Movement Study results
The movement study provides useful evidence of direct linkages between some sites, as well as suggesting a more general pattern of bird behaviour. Typically, as the tide rises birds (especially in the case of waders) move from intertidal feeding areas as they are covered by the tide and to a small number of preferred staging areas. From these sites, feeding flocks then branch to a larger number of terrestrial sites, as well as moving directly between onshore sites (Figure 5 2). In particular, the islands in Langstone Harbour offshore from Farlington Marshes LNR seem to be of particular importance for the movement of flocks.
Identification of movement networks
Figure 5 2 Brown lines show movement of waterbird flocks (all species combined) between separate sites included in the study (green shaded areas).
When the bird movements were plotted in network diagrams, abstracted from geographical context, two trends can be seen more clearly: the division of the whole area into distinct subnetworks, and the role of some sites as ‘hubs’ within those sub-networks, or ‘bridges’ between two sub-networks (Figure 5.3).
Average flight distances literature review
Published distances between roosting and feeding sites, or between feeding sites themselves, are highly variable (e.g. Symonds et al, 1984; Dias et al., 2006; Catry et al., 2011). This variability is partly due to different methods used to derive estimates: for example, bird-
Figure 5 3 Network diagram of waterbird flock movements around the Solent. Offshore sites are represented by blue circles, coastal sites and inland waters by yellow circles, and terrestrial sites by green circles. A link joining two sites indicates that at least one movement of waterbirds between those sites was recorded.
marking studies of the catchment of a roost, based on resighting feeding birds away from a roost where they were marked, typically show a large catchment area. On the other hand, studies using tracking methods, that can show the distances travelled for each individual movement, generally show much shorter movements.
The distance that birds can travel between sites depends on the quality of feeding resources, frequency and severity of disturbance, availability of alternative sites, climate and exposure to weather, as well as on the species in question. (e.g. Burton et al, 1996, Choi et al, 2011, Dias et al, 2006) For these reasons, even if estimates were published for other locations, it would be difficult to extrapolate robust conclusions that would apply to the Solent
Linkages between feeding and roosting areas literature review
Previous studies have demonstrated that the loss of suitable high-tide roost sites renders otherwise-suitable feeding areas unusable by birds (e.g. Dias et al., 2006). Establishing this catchment area should therefore be a priority for management-focussed research. However, given the many sources of variation in published estimates of the catchment area noted in Section 5.2.2, any attempt to rely on published literature would have to be extremely conservative. If a proposed development would have an adverse effect on protected populations according to that conservative estimate, a robust study of the relevant area and species, using modern tracking technology (López-López, 2016), would be required to adjust expectations of the developments impacts.
5.3.
Other data collected to inform the study
Anecdotal Evidence
In addition to data collation and conducting our own surveys, we asked birdwatchers who regularly cover a section of the Solent to record their local expertise about birds site usage and movements between areas. In general, these reports largely focused on offshore feeding and roost sites, and movements between them.
Here, we compare the evidence provided by two local experts, from Gosport and Chichester Harbour, with the results of the Coastal Network Study analysis.
5.3.1.1. Gosport
Figure 5 4 Anecdotal evidence of waterbirds' site usage and movement (green shapes and arrows) patterns in the Gosport area, according to local evidence, shows patterns very similar to sites' classifications in the Coastal Network Study (coloured polygons). Most locations have numerous records collected during the CNS (purple dots). Mapping is showing SWBGS classification which are to some extent interchangeable, primary = critical, Secondary = Auxiliary and Low-use = Potential.
5.3.1.1.1. Positive records
The Gosport local expert identified 9 'main Brent Goose feeding areas' and 15 other areas used for feeding or roosting by Brent Geese (Figure 5 4). Of the 'main' areas, 8 out of 9 were classified as 'critical network sites' in our analysis, with the one remaining site in the Auxiliary network. Of the other areas identified by the local experts, five were offshore and the remaining 10 were classified as secondary habitats.
Every location identified as used by the local experts is supported by several records from this study, primarily the Solent Birds app, including locations outside the priority survey areas targeted by this study. Furthermore, the local experts identified the main routes taken by Brent Geese flying to their evening roost-site, which was confirmed by the Bird Movement Study.
5.3.1.1.2. Negative records
Six sites were identified by the local observer as unused (by Brent Geese), little-used or unsuitable, and one as uncertain. The uncertain site, and 4 'unused' sites, were classified as data-deficient; the remaining 'unused' site was classified in the auxiliary network, as it held a locally-important number of Grey Heron. It seems probable that many data-deficient sites receive few visits because they are known to be unsuitable habitat for the target species.
5.3.1.1.3.
Summary and conclusions
Therefore, our categorisation of Gosport sites concords closely with local expert opinion as to the value of sites for Brent Geese, even though our analysis included data from other waterbird species. However, the local experts mentioned only 8 (57%) of critical sites, 11 (37%) of auxiliary sites, and 6 (13%) of the potential or data-deficient sites, within the borough
5.3.1.2. Chichester Harbour
Figure 5 5 Partial results for Curlew from the Chichester Harbour expert, showing the locations of important terrestrial sites (green arrows), offshore roosts (black arrows) and high-tide movements (orange arrows). Red dots indicate approximate densities of birds feeding in the intertidal at low tide.
5.3.1.2.1. Waders
Terrestrial sites used for feeding or roosting were identified by the local expert for three species: Black-tailed Godwit, Curlew (Figure 5.5) and Oystercatcher. Their classifications in the Coastal Network Study are shown in Table 5.1
Of well-used sites in Chichester Harbour, around 20% are in the critical network and 80% in the auxiliary network, matching the pattern for Oystercatcher only. Sites considered important for Black-tailed Godwit or Curlew were disproportionately likely to be in the critical network.
This may reflect the classification procedure itself, as it gives more weight to godwits and curlew which are designated features of interest in the Chichester and Langstone Harbours SPA. However, it may also reflect that these species are more restricted in their habitat use, occurring only in highly-suitable sites.
Table 5.1 Number of terrestrial sites identified as important for each wader species by the Chichester Harbour local expert, and their classification in the Coastal Network Study.
Movements of Dunlin, Grey Plover, Knot and Redshank between Chichester and Langstone Harbours were noted by this expert. Few such movements were detected in the Bird Movement Study, as the routes taken by birds were generally not visible to observers, but previous records exist in the form of the Movement in the East Solent Harbours (MESH) study (de Potier and Bradley, 1999).
5.3.1.2.2. Brent Geese
Furthermore, a large number of general areas were identified as used by Brent Geese, but it was noted that the exact field changes on a yearly basis with cropping patterns, as there is a large amount of potential habitat available. This comment reinforces the need for a longitudinal study of habitat types and use by Brent Geese (and other species), as most of the data collected for the present work is from within the last 5 years.
5.3.1.3. Summary
In general, anecdotal evidence was sufficiently close to the formal analytical results from the CNS to be considered accurate. However, they are generally less precise, and have some omissions.
This is because, in essence, the Solent Birds app harnesses the opinions of multiple local experts, many of whom are regular recorders. The strength of the app is that those opinions are instantly backed up with data, and also includes ad-hoc records from more itinerant birdwatchers, allowing a greater spatial coverage, regular updates and robust numerical support.
Results from Gosport suggest that the majority of data-deficient sites may have little-used or have unsuitable habitat and are certainly unlikely to be of Critical-network importance. The observation of between-year variance in site usage by Brent Geese highlights the importance of studying the effect of changing cropping patterns on the distribution of this species.
5.4. Limitations of the data
Data collection
The main difficulty observers faced was visibility. Inland areas are very often obscured behind trees, topography and/or buildings. Offshore feeding areas may be very distant, low-lying and crossed by networks of creeks rendering flocks hard to detect. Commonly, flocks were only detected after they had been flying for some time, and in these cases their origin could not be reliably determined. Finally, the sinuosity of the coastline meant that even when birds were
moving between onshore roost sites, it was often impossible for a single surveyor to identify both the start and end points.
It is also common for several flocks to be moving simultaneously, or for one flock to split into several parts, with different destinations. Under these circumstances it is difficult or impossible for a single surveyor to keep track of all movements.
These factors were exacerbated by the typical suite of conditions that are the scourge of fieldworkers, such as heavy rain and strong winds, both of which were commonplace during the survey period.
Data interpretation
The analytical method described in Section 5.1.2 can be used to produce a map connecting all recorded bird movements in the study area (see Figure 5.3). However, the ultimate goal of our study was to prioritise sites for protection. We prioritised sites based on the number of movements to and from that site, which was intended to give an estimate of the site’s “popularity” with waterbirds. However, within the study area there is a severe disturbance gradient, where disturbance is common in (for example) Gosport and Portsmouth fields, whereas those around Chichester Harbour are rarely disturbed. This confuses interpretation of the results, as in Chichester Harbour a flock can feed in a single location for hours; that site may in fact be more valuable than a site from which birds are frequently disturbed (or may not) but would not be picked up by the movement surveys.
It was also very difficult for analysts to confidently reconstruct single movements from multiple surveyors’ data. During the rising tide many flocks are moving, and counts of their size are typically estimates with some associated error. It was therefore challenging to link a flock seen departing by surveyor A with a particular flock seen arriving elsewhere by surveyor B.
Additional considerations
We found that, during neap tides, very few long-distance movements of birds were observed, probably because birds are able to roost on the upper intertidal adjacent to their feeding areas at these times (Rosa et al., 2006). In order to gain a more robust sample of recorded movements we therefore focussed our efforts closer to spring tides. This was appropriate in our case, as we were particularly interested in onshore roost sites, and those that might need protection under conditions of sea level rise and coastal squeeze. However, studies intending to record all roost sites used would need to record movements across the tidal cycle.
Furthermore, some of the results were obtained through the use of volunteer recorders, some of whom were not birdwatchers. Over half of movements records submitted were of Brent Geese, which are large and easily identified, despite being outnumbered by small waders. There is therefore likely to be a bias in results collected by lower-skilled volunteers towards the more obvious and distinctive components of the waterbird assemblage.
5.5. Alternative options for investigation of bird movement
Existing ringing data
Analysing the data from waterbirds already ringed in the Solent was deemed unsuitable for meeting the key objective of the bird movement study: identification of links between feeding
and roosting sites. This is due to three issues, the applicability, age and availability of these data, identified during preliminary discussions with local ringers.
5.5.1.1.
Applicability
In order to identify links between feeding and roosting areas, one would need a significant number of birds to be captured or sighted at both a feeding and a roosting area, preferably within the same tidal cycle or at least within a few days. However, most ringing data collected so far has been generated by volunteers for the purposes of studying international movements (e.g. Potts, 2008), population sizes (e.g. Gunnarsson et al., 2005) or for demographic monitoring (e.g. Robinson et al., 2005); therefore, the methods of data-collection employed usually render the data unsuitable for our purposes.
Most birds are fitted with a metal ring only, which means that confirming individuals’ movements depends on capturing the same birds repeatedly in different places (Redfern and Clark, 2001). For most waterbird species in the Solent, metal-ringing is the only method ever undertaken. Recovery rates (including dead birds) for waterbirds vary from around 10% for geese and swans down to <1% for waders such as Dunlin, Curlew and Redshank (Robinson et al., 2009). Consequently, for most species, sample sizes are likely to be inadequate.
Furthermore, captures are typically at high-tide roost sites only (Clark et al., 2004), as the soft substrate, distance from shore and narrow tidal window of opportunity all make capturing birds at intertidal feeding sites impractical. Recaptures demonstrating linkages between feeding and roosting areas are therefore especially unlikely.
For some species, Farlington Ringing Group has used unique colour-ring combinations to track species (e.g. Brent Geese, Black-tailed Godwit, Redshank, Greenshank and Sanderling). These combinations can be read in the field, obviating the requirement to recapture birds, allowing more records and therefore more precise estimates from small samples compared to metal-ringing (Robinson et al., 2005). However, records of these birds are typically obtained from roosting areas, as reading the combination accurately is only possible over short distances. Furthermore, the resighting data is collected by volunteer observers in a non-targeted manner, making the likelihood of recording same-day movements between feeding and roosting areas unlikely.
Finally, even when targeted work has been undertaken for this purpose, confirming same-day movements has proven to be difficult using traditional methods (Norton and Demopoulos, 2000). For example, during the enquiry relating to ABP’s proposed development of Dibden Bay in the western Solent, colour-ringing of three species yielded few observations (Table 5.2).
Table 5.2: Sample sizes from targeted colour-ringing fieldwork in the Solent (reported in Norton and Demopoulos, 2000).
5.5.1.2. Quantity and age of data
Bird-ringing is a skilled practice requiring years of training and special licensing; this is especially true of cannon-netting, the main method used to catch large samples of waders (Redfern and Clark, 2001). Therefore, the number of people able to conduct catches in the local area is very limited.
Due to the unavailability of key personnel, very little waterbird ringing has occurred since the winter of 2015/16, meaning that by the time of this report’s publication the most recent data will be 3 years old. Due to the likely scarcity of records meeting the criteria for inclusion, most would be considerably older.
5.5.1.3. Availability
All catching and the vast majority of resighting effort has been performed by volunteers at considerable personal expense, involving thousands of person-hours per year. Discussions with local ringers indicated that the data generated by these efforts would not be available to a funded project free of charge, but rather would attract a fee at commercial rates for their collation and distribution that would reflect the costs of data collection.
5.5.1.4. Conclusion
While a bespoke study involving colour-ringing and targeted resighting fieldwork would generate useful insights into birds’ daily movements, as well as issues such as turnover at roosts, we considered it unlikely that a broad analysis of ad-hoc historical ringing records would bear much fruit.
Analysing data from historically colour-ringed birds would help to contextualise any new study and enable interpolation of results over a longer timeframe. However, tackling the questions of the Bird Movement Study is likely to benefit from using more modern bird-tracking techniques (López-López, 2016).
Bespoke bird movement study options
Here we provide an overview of methods for studying bird movements, covering the most widely-used technologies as well as some emerging techniques. Approximate costs for a strategic bird movement study in the east Solent harbours are provided.
The projects described below would be aimed towards providing statistically valid results for five species: large and small waterfowl (e.g. Brent Geese and Wigeon) and three sizes of wader (e.g. Curlew, Redshank and Dunlin). The studies envisaged are for a strategic overview of the eastern Solent harbours: smaller, site-focused studies could reduce certain costs (e.g. colour-ring resighting effort).
Note that the costs presented are for data collection only, and do not include expenditure on project administration, data analysis, report writing, etc.
5.5.2.1. Capture methods
Before any marks can be applied, birds need to be caught. There are two effective methods for catching waterbirds, cannon-netting and mist-netting. Catching is generally easier at hightide roosts (Clark et al. 2004), as birds are more concentrated than when feeding. Cannonnetting can deliver large samples, but the success of catch attempts, and size of successful catches, is somewhat unpredictable, as flock behaviour varies daily. Mist-netting is a more flexible method, but generally delivers smaller samples per catch attempt, and is only suitable for smaller species. A large study would likely need to employ both methods.
5.5.2.1.1. Cannon-netting costs
• Equipment is custom-made and therefore expensive, but can be rented from ringing groups. Guide cost: £50/catch.
• Consumables (e.g. fuses, black powder). Guide cost: £35/catch.
• Catch organisation takes several visits to ascertain bird behaviour and site use, followed by at least one (more for larger catches) BTO cannon-net licence-holder being present to direct proceedings at the catch itself. Guide cost: £500/catch.
• Team mileage: A large team (10+), including several experienced bird-ringers, is needed to ensure the safety and welfare of birds when using cannon-nets, especially when catching in water. While team members time may be available on a voluntary basis, for commercial work it is customary to cover regular participants’ transport costs. Guide cost: £50/catch.
5.5.2.1.2. Mist-netting costs
• Equipment is less specialised and less expensive, but more prone to wear-andtear. No consumables. Guide cost: £20/catch.
• Catch organisation is less intensive as birds can be attracted using tapes, and more licence-holders may be available. Guide cost: £350/catch
• Team mileage: Teams are smaller, and again may be volunteers with transportation covered. Guide cost: £25/catch
5.5.2.2. Tracking methods
5.5.2.2.1. Colour ringing individuals
Captured birds are marked with unique combinations of coloured plastic rings which allow individuals to be re-identified after they are released. Resighting of birds by volunteers and recreational birdwatchers tends to be opportunistic and biased towards popular birding sites and easily recorded locations, necessitating a program of standardised resighting effort to provide interpretable results. For the purposes of the Bird Movement Study – understanding connections between roosting and feeding areas – birds would ideally be recorded at both high and low tide during the same day.
5.5.2.2.1.1. Sample size
The important number for analysis is the total number of independent re-sightings, which is a function of both the number of birds marked and resighting effort; furthermore, larger species generate more sightings than smaller ones due to the ease of reading rings. Estimated necessary sample sizes therefore vary between species:
• Large species (e.g. Brent Goose, Curlew): 50
• Medium (e.g. Redshank, Wigeon): 100
• Small (e.g. Dunlin): 150
However, for estimating costs, the number of capture attempts is also important. While this is highly variable and unpredictable, around five attempts per species should generate the sample sizes above.
5.5.2.2.1.2. Costs
• Cannon-netting: £635 per catch × 5 catches × 5 species = £15,875
• BTO metal rings: 1 per bird, cost varies per species:
o Brent Goose: £70 / 50 rings
o Curlew: £15.00 / 50 rings
o Dunlin: £20 / 150 rings
o Redshank: £13 / 100 rings
o Wigeon: £15 / 100 rings
o Total: £133 / 450 birds
• Colour rings: Several per bird, (total) cost varies per species:
o Brent Goose: £5 / bird
o Curlew: £1.80 / bird
o Dunlin: £1.80 / bird
o Redshank: £1.80 / bird
o Wigeon: £1.80 / bird
o Total: £880 / 450 birds
• Resighting: Reading colour-rings (correctly!) is an acquired skill; even experienced birdwatchers are prone to error. It is therefore recommended to use experienced recorders to ensure both data quality and quantity. Resighting can take place throughout the day, in inland fields, at coastal roosts (at high tide) and at offshore feeding areas (at low tide), so prices quoted are for a full day’s effort:
o 30 person-days × 5 species × £150 / day = £22,500
Estimated total costs for a colour-ringing study in the Solent are set out in Table 5.3. It should be noted that these costs are based on using a largely volunteer ringing team.
5.5.2.2.1.3. Advantages
• Applicable to species of all sizes
• History of colour-ringing in Solent means a longer timeseries of opportunistically collected resighting data could be purchased and analysed
5.5.2.2.1.4. Disadvantages
• Collection of location data effort-intensive and dependent on quality observers
• Little-to-no data on direct movements, or movements within single tidal cycle
• Many feeding areas and some roost sites not visible from shore (and therefore would not yield any data)
• Data available only from daytime
Table 5.3 Illustrative costs of a colour-ringing study (prices correct 2018)
5.5.2.2.2. Smart tags
Birds are captured and fitted with electronic tags which record birds’ locations using GPS. These data are then downloaded remotely, either via satellite (for larger tags on larger species >600 g), or over UHF radio (for smaller species >165 g).
For each species the chosen tag and attachment method must be individually approved by the BTO, a process which can take many months. Currently, GPS tags are not available for species <165 g, excluding Redshank- and Dunlin-sized birds from smart-tagging studies.
Due to the greater accuracy of data and increased number of locations per individual, meaningful conclusions can be drawn from smaller samples of birds: three catch attempts averaging 20 individuals per species would enable sampling birds from various locations.
5.5.2.2.2.1. Costs
• Catching and ringing costs as above, but based on three catch attempts / 20 individuals per species (per comms BTO, 2017)
• Tags:
o Brent Goose: GPS/GSM (satellite) tags: £1050 / bird
o Curlew & Wigeon: £732 / bird
o Redshank & Dunlin: not applicable
Estimated total costs for a limited smart tagging study in the Solent are set out in Table 5.4.
Table 5.4 Illustrative costs of a smart-tagging study (prices correct 2018)
5.5.2.2.2.2. Advantages
• Highly accurate data
• Little resighting effort necessary (repositioning UHF data-receiver requires little skill)
• Data available in real-time for rapid decision-making
• Opportunities for public outreach via online bird-tracking portal
• Data available for night-time site-use
5.5.2.2.2.3. Disadvantages
• Higher financial cost
• Not available for small species
5.5.2.2.3. Dye marking Birds are captured as described above, and pale areas of plumage are dyed. Only two colours are available (and only one that lasts several months), so it is not possible to make individuals identifiable; instead, this method is suitable only for following cohorts, for example the feeding
catchment of birds from a particular roost (e.g. Dias et al., 2006), by marking different parts of the bird (e.g. left wing, right wing, breast, etc) in different locations
This method still requires resighting effort, though not necessarily using such skilled observers. This costing is based on the same sample sizes as proposed for the colour-ringing study.
5.5.2.2.3.1. Costs
• Catching and ringing costs as Colour-ringing, above
• Plumage dye estimated at £0.05 / bird
Estimated total costs for a dye-marking study in the Solent are set out in Table 5.5.
Table 5.5 Illustrative costs of a dye-marking study (prices correct 2018) Species
£38,531
5.5.2.2.3.2. Advantages
• Marking and recording marked birds are comparatively straightforward
5.5.2.2.3.3. Disadvantages
• Requires intensive fieldwork for resighting dyed birds
• Many feeding and roosting areas not visible from shore
• Limited number of locations can be differentiated.
• No data about individuals
• No data from night or poor weather
5.5.2.2.4. Radar ornithology
Radar ecology or aeroecology is a fairly new discipline involving the study of the movement of organisms as detected by and interpreted from radar emissions (Stepanian, Chilson and Kelly, 2014). Radar (Radio Detection and Ranging) is a well-established technology mainly used for detecting and tracking aircraft and shipping, navigation and also meteorology. Radar reflectance from birds, bats and insects called ‘bioscatter’ has been known to interfere with radar images and has to be filtered out for the purposes of weather forecasting and aircraft tracking. However, more recently this filtering has been used to detect ‘bioscatter’ for ecological studies and for the reduction of aircraft bird strikes.
The technology can provide real time data on biological targets such as birds within range of the sensor, but more often requires considerable post-processing of the data. Ecological
studies tend to either use data derived from existing sensors (e.g. ground based aircraft tracking station and weather radar) or bespoke avian radar systems. Using data from existing sensors has obvious advantages in terms of cost: if the data is available the only cost is processing to extract the data of interest and the data is recorded continuously providing longterm datasets. Mobile avian radar has the advantage of being calibrated specifically for tracking biological targets, providing greater resolution (including stated ability to identify to species level) and ability to site the sensor for the best coverage of the subject area.
5.5.2.2.4.1.
Applicability
The utility of using radar to track bird movements within the Solent was investigated through contacts with ENRAM (European Network for the Radar surveillance of Animal Movement) and the UK APHA (Animal and Plant Health Agency).
Existing installation: Use of existing radar installation data was quickly discounted, as radar can only operate on a line of sight basis, i.e. the radar needs an unobstructed view of the area, without buildings, topography or vegetation to block the radar signal. Therefore, only birds flying higher than surrounding topography can be detected. Furthermore, coverage by air traffic control and weather radar installations is wholly inadequate for the purposes of this study: Primary radar tracking for air traffic control only covers certain parts of the UK (which doesn’t include the Solent), and the nearest weather radar is Dean Hill near Salisbury, 20-70 km from the study area. In the case of this study we are interested in the relatively small scale tidally or circadian movement of birds. From what we know about the habits of birds and the nature of the topography, it is unlikely that existing data and radar installations would provide useful data.
Mobile avian radar: Current systems can cover an area up to a 22 km radius, and operators claim that if calibrated by visual observations it is possible to identify birds to species level. However, the line of sight limitation would mean that multiple locations would be required to get adequate coverage of an individual site. For example, three to four locations would be needed to cover Langstone Harbour; therefore, concurrent coverage would require three to four systems to be deployed simultaneously. Alternatively, the mobile unit could move locations to cover the area, but this would require more time and lose the ability to get a concurrent picture of an entire area of interest. Extrapolated up it would take in the region of 20-25 survey locations to provide something like adequate coverage of the Solent. It is also understood there are only two or three mobile avian radar units currently available in the UK.
5.5.2.2.4.2. General discussion
Standard practice is to operate an avian radar for a 24 hour period to get a picture of the circadian and in this case tidally induced movement patterns. To gain a fuller understanding would require repeated deployments to cover a range of tidal conditions and seasonal coverage.
Other limitations of the approach would relate to the ability to identify to species level and the difficulty of tracking individuals. Although operators and suppliers claim to be able to identify birds to species level, it is not considered that accuracy of results could approach that gained by an experienced observer using optical equipment. However, it is accepted that the technique could provide identification to species group or size classes e.g. small wader, medium duck, etc.
Radar cannot track individuals, which would fill gaps in our knowledge about how birds use an area, e.g. the throughput of birds on a daily, seasonal and tidal basis, which for most species is unknown. Visual observations also fall foul of this limitation, but radar compounds
it through the difficulty of detecting grounded targets. For example, a flock of 50 birds flies from point A to point B, then a group of 50 birds flies from point B to point C: with radar data there is no way to tell if this is the same 50 birds or two groups of 50. It does, however, have the advantage over visual observation of being able to operate 24 hours a day, recording everything for later analysis and covering a wide area simultaneously. Radar is also affected by weather conditions e.g. rain and fog, though perhaps to a lesser extent than visual surveys.
5.5.2.2.4.3. Costs
Estimated total costs for an avian radar study in the Solent are set out in Table 5.6
Table 5.6 Illustrative costs of an avian radar study (prices correct 2018 to contract a radar operator)
5.5.2.2.4.4. Advantages
• Simultaneous coverage of wide survey area
• Nocturnal data collection
• Price includes professional data interpretation
5.5.2.2.4.5. Disadvantages
• Can be blocked by topography
• Vulnerable to adverse weather conditions (e.g. fog, rain)
• Cannot identify individuals
• May not be able to identify birds to species
5.5.2.2.5. Vantage point surveys
Skilled observers are positioned in strategic points around the focal area during the high-tide period, and record bird movements: the species, origin and destination of every flock observed moving.
Due to difficulties ascertaining origins and destinations of flocks in flight, as well as in seeing (and identifying birds over) long distances, a large number of repeat surveys is required in order to get sufficient data to have a statistically robust understanding of the patterns of bird movements in the focal area. Furthermore, in areas with complex coastlines, many observers may be required to overcome the difficulties of topography.
5.5.2.2.5.1. Costs
Estimated total costs for an expanded vantage point study in the Solent are set out in Table 5.7
Table 5.7 Illustrative costs of expanded vantage-point survey studies
5.5.2.2.5.2. Advantages
• Does not require capturing/marking birds
• Records direct movements between sites within single tidal cycle (where possible)
5.5.2.2.5.3. Disadvantages
• Difficulty observing complete movements: in practice, origin and/or destination often not observed
• Lack of traditional framework for analysing and interpreting results
5.5.2.2.6. Cost / benefit analysis
An analysis of the costs, benefits and constraints of the alternative tracking methods discussed above has been undertaken and is summarised in Table 5.8
Table 5.8 Approximate project costs and data characteristics for the various study methods discussed in more detail above.
It is clear that certain approaches will be prohibitively expensive in proportion to the additional benefit provided by gaining that data. It will also only give a snapshot in time and how applicable attempting to undertake such a study at a strategic level will be in indeterminate.
6. Summary of recent Habitats Directive case law
In recent years there have been several authoritative rulings from the Court of Justice of the European Union (CJEU) in relation to the Habitats Directive and, consequently, the Conservation of Habitats and Species Regulations (2017) as amended. This case law has clarified the Habitats Regulations Assessment (HRA) process and drastically reduced the flexibility around habitat impacts, in particular where a plan or project will result in permanent habitat loss within a European site. The key rulings from the CJEU relevant to the Solent Bird Studies and Solent FCERM schemes are summarised below.
Sweetman (C – 258/11)
In April 2013, the “Sweetman” decision from the CJEU considered what is meant by the Habitats Directive test of “adverse effect on integrity of the site”. In this case the CJEU ruled that the permanent loss of part, even a very small part, of a habitat for which a European site was designated must be regarded as adversely affecting integrity where the habitat is a priority type listed in Annex 1. This ruling did not include a decision on how far this principle applies to non-priority habitat types. However, the Court did make clear that the integrity of the European site means that it has to be preserved at favourable conservation status. This means there has to be lasting preservation of the characteristics of the site connected to the feature(s) for which the site was designated. Therefore, an appropriate assessment of a plan or project needs to consider the effect on the European site and its conservation objectives when determining whether or not that plan or project will have an adverse effect on the int egrity of the site.
Briels (C – 521/12)
In May 2014, the CJEU handed down a judgment in the “Briels” case. This case considered what types of measures are relevant to take into account as mitigation when determining whether a plan or project will have an adverse effect on integrity of a European site under Article 6(3) of the Habitats Directive (i.e. in the appropriate assessment stage). The Court ruled in this case that habitat creation is a compensatory measure rather than mitigation because it does not lessen or avoid a negative effect on a site but rather seeks to counterbalance after the fact for the effect of the project. Consequently, habitat creation measures cannot be taken into account at the appropriate assessment stage under Article 6(3) but should be considered as a compensatory measure under Article 6(4) of the Habitats Directive. Therefore, habitat creation measures should not be considered until later in the formal Habitats Directive decision making process, i.e. after consideration of alternative solutions and only after establishing imperative reasons of overriding public interest (IROPI).
Hilde Orleans (C – 387/15 and C -388/15)
In August 2016, the “Hilde Orleans” ruling provided further clarification around the consideration of habitat creation measures in the Habitat Directive decision-making process. In this case, the CJEU ruled that positive effects of habitat creation which take place before the original habitat is lost but after the Habitats Regulations Assessment had been undertaken was likely to leave reasonable scientific doubt as to significance of any effect, and so could not be considered as mitigation to rule out an adverse effect on site integrity. In making this ruling the CJEU indicates that new habitat must be created and functioning successfully before the appropriate assessment is carried out and, therefore, before any adverse effects associated with the plan or project take place. This principle severely limits the practical application of habitat creation as a mitigation measure as it requires significant investment in
the habitat creation before it is known whether consent could be secured for the development plan or project.
Implications of CJEU case law for Solent FCERM schemes
The recent CJEU case law provides authoritative interpretation of how permanent habitat loss within European sites should be considered in a HRA. The case law indicates that habitat loss resulting from Shoreline Management Plan (SMP) policies and FCERM scheme delivery within a European site in the Solent should be considered to have an adverse effect on the integrity of the designated site. Therefore, implementation of SMP policy and FCERM projects should only be able to proceed once it has been demonstrated that there are no suitable alternative solutions, there are imperative reasons of overriding public interest (IROPI) and suitable compensatory measures have been agreed.
It has already been demonstrated within the HRAs for the North Solent SMP and the Isle of Wight SMP that there are no feasible alternative solutions to the preferred SMP policies that would have a lesser effect on the integrity of the European sites. Furthermore, the HRAs for the North Solent SMP and the Isle of Wight SMP demonstrated IROPI and confirmed that compensatory habitat creation measures will be delivered strategically for the Solent European sites via the Environment Agency’s Solent and South Downs RHCP. Environment Agency Habitat Creation programmes are the Government’s recommended vehicle for delivering strategic habitat compensation and are funded in advance of engineering works that cause damage. Therefore, no damage to a site as a result of a policy should occur, prior to compensation being secured and delivered. In taking this approach, habitat creation to offset losses from SMP policy and FCERM scheme implementation will be delivered strategically as a compensatory measure, and not via piecemeal mitigation measures at the individual scheme level. This will ensure it is both compliant with CJEU case law and delivers ecologically functional habitat creation to ensure that the coherence of the Natura 2000 network is protected.
7. Using the Solent Bird Studies
The following section explores the implications arising from the Solent Bird Studies for various matters and the ways in which the data and findings can be used to support decision making in other fields. In fact the data and findings of the study have already been used for a number of purposes;
• Data collected through the SolentBirds app formed a significant proportion of the records used within the SWBGS analysis.
• The Solent Bird Studies has been used to assess sites for the Regional Habitat Creation Programme (see case study)
• Data and advice has been provided to Havant Borough Council in relation to Local Plan site allocations and the development of a proposal for a strategic brent goose refuge scheme.
• Solent Bird Studies data was used to support the Environmental Impact Assessment for the now cancelled Southmoor habitat creation scheme.
• The data has been used to assess the potential to harm important bird sites for a number of planning applications across the Solent.
• The data has been supplied to Hampshire Biodiversity Information Centre, Sussex Biodiversity Record Centre, the Isle of Wight County Bird Recorder and Natural England.
7.1. Implications for Habitat Compensation Programmes
Rather than ‘putting all your eggs in one basket’, a bet-hedging strategy, providing numerous sites with different aspects across the target area, ensures that suitable sites which provide shelter are always available, as well as providing alternative sites in the event of disturbance e.g. the provision of simple artificial structures like jetties and piers (Gabbard et al., 2001).
Lagoon systems, such as the salt-pans common in sunnier climes, have good potential to support waterbirds, and also function as supplementary feeding areas (Masero et al., 2000; Warnock et al., 2002). In the Solent, protecting the lagoon walls at the Oysterbeds (West Hayling LNR), would secure what is already one of most important roosts, but needs protection from erosion. Enlarging the artificial islands in the lagoons centres would also enhance the sites attractiveness as a roost, as those areas would be better sheltered and offer 360° visibility; these islands would also support breeding terns in the summer. The lagoon-system design of the Oysterbeds could even be expanded locally, or replicated elsewhere, to offer additional roosting and foraging habitat
Various sites’ attractiveness as roosts for geese and waders could be improved by vegetation removal to improve visibility (Peters and Otis, 2007). For example, the trees on playing fields and developing scrub on various coastal grazing marshes reduce suitability as roosts, as birds avoid roosting close to tall cover (Rogers et al., 2006). While no formal analysis of historical site use has yet been undertaken, it is anecdotally recorded that many playing fields and golf courses which used to support large flocks of e.g. Brent Geese, Dunlin and Grey Plover now support only a few Black-headed Gulls, during the same time that trees have grown and scrub cover increased. Currently, many apparently suitable sites are rendered unsuitable due to their proximity to tall vegetation. If the sites are genuinely otherwise valuable as roosts (e.g. low disturbance), tree removal and/or modified grazing regimes are rapid and relatively inexpensive methods to increase the area of suitable roosting and foraging habitat.
Protection from disturbance is itself an important factor, which is likely to be best achieved through hard measures like fencing to prevent access and/or screen people and dogs from roosting birds’ views. Watercourses can also act to prevent access. Where new sites are created, it is simple to design them such that they are undisturbed, even if recreational use of the site by birdwatchers is a parallel objective (e.g. Kitchen and Young, 2007). On the other hand, where sites are physically accessible, signs are easily and routinely ignored, and it is not possible for all sites to be proactively monitored against disturbance during every tide.
Case Study- Conigar and Warblington Intertidal Habitat Creation
Using Solent Bird Study data for RHCP site appraisals.
The Regional Habitat Creation Programme (RHCP) is a nationally adopted, strategic and proactive approach delivery mechanism to compensate the impacts of coastal squeeze from FCERM schemes. In the Solent and Southdowns region the RHCP is charged with delivering coastal squeeze derived habitat creation requirements for three Shoreline Management Plans (North Solent, Isle Of Wight and Selsey Bill to Beach Head). Over the
100 year span of the programme approximately 500ha of intertidal habitat needs to be created.
The Environment Agency (EA) and Coastal Partners have been working together on updating the habitat targets and identifying suitable sites for habitat creation projects going forward. The following is a case study of how Solent Bird Studies data and findings were used to appraise options for a site, identifying potential impacts as well as opportunities for enhancements for the site and hinterland.
Potential habitat creation sites
The Solent Dynamic Coast Project (Cope et al 2008) identified a number of sites across the Solent as being suitable for managed realignment. These sites were included as potential intertidal habitat creation opportunities by the RHCP and a subset of these sites have been identified as priorities for early consideration. Of these, two sites one at Warblington and a further site at Conigar Point were identified as candidates, although they will each create discrete areas of intertidal habitat, due to their close proximity it was decided to consider them as a combined project.
One of the concepts that were considered when appraising sites was to attempt to provide an integrated solution wherever possible, so that all potential mitigation arising at the scheme level should be delivered within the same scheme, rather than passing it back to the RHCP. It would also propose that the process should consider how ‘Net Gain’ could be delivered by the schemes, through enhancements to biodiversity.
Using the Solent Bird Studies data, it was determined that the Conigar Point site was classified as critical network and therefore managed realignment could lead to a loss of its function as a wader roost and inland feeding area for wildfowl. It was further noted that the land between the two habitat creation sites is also classified as critical network and a further critical network site was located adjacent to Conigar Point. Whilst it was not felt the scheme had the potential to harm these sites, it did provide an opportunity to undertake mitigation
Figure 7.1- Modelled extent of potential habitat creation at Conigar and Warblington
within the site and an opportunity to secure positive management on a key part of the Solent network of sites.
Figure 7.2-Solent Bird Studies sites in proximity to potential habitat creation site.
It was therefore decided that any future habitat creation scheme should secure the two critical network sites as part of the proposal to enable any impacts on functionally linked land important for over-wintering birds to be mitigated within the scheme. This also enables space to be given to allow a succession of habitats migrate upstream and represents a significant ‘Net Gain’ for biodiversity in terms of over-wintering bird use and habitats.
7.3- Proposed scheme boundary incorporating additional land to provide mitigation, ‘net gain’ and allow upstream migration of habitat.
7.2. Implications for Site Management
There is considerable literature on roost site characteristics. Here we have attempted to summarise the key features of wader roost sites, with an emphasis on factors that can be controlled or mitigated as part of site management or incorporated into the creation of new sites through the RHCP.
What types of artificial structures do waders use?
Waders roost on sea walls (Unsworth, 1994; Farrell et al., 2016), piers (Burton et al., 1996; Gabbard et al., 2001), fishponds (Luís et al., 2001; Choi et al., 2014), salt pans (Masero et al., 2000; Luís et al., 2001; Warnock et al., 2002; Dias et al., 2006; Rosa et al., 2006), artificial islands (Burton et al., 1996), pasture (Conklin and Colwell, 2007), as well as purpose-built roost sites (Burton et al., 1996; Kitchen and Young, 2007).
What characteristics make good roost sites?
A previous study of roost characteristics in the Solent (Liley and Sharp, 2010) produced a model which could successfully determine which sites would definitely not be used by birds, but had low predictive power to determine which, of the many apparently suitable sites, would actually be important roost sites. This is likely to be because of two factors. One is that waders habitually return to traditional roost sites. The other is that, on any given day, the best roost site will vary depending on various deterministic (e.g. tide cycle) and stochastic (e.g. weather; presence of disturbers/predators) factors.
Figure
However, the published literature has consensus on a number of important factors, most relevant of which are:
• Location is key: waders preferentially roost as close as possible to their feeding areas (Dias et al., 2006; Rogers et al., 2006; Zharikov and Milton, 2009).
• Disturbance from people and boats has a strong, negative effect on roost site usage (Smit and Visser, 1993; Fox and Madsen, 1997; Luís et al., 2001; Peters and Otis, 2007).
• Shelter from weather conditions such as wind, rain, spray and waves are all important (Luís et al., 2001; Peters and Otis, 2007).
• Avoidance of predation through good field of view (Luís et al., 2001; Rosa et al., 2006; Zharikov and Milton, 2009).
7.3. Use for planning decisions
In section 4.6.2 the findings of this study were compared to planning allocation sites In total, there were 88 Solent Bird Study sites that overlapped with planning allocations, including 42 residential, 17 employment and 29 mixed use allocations. Of these; 46 were sites with sufficient data to make a determination of their importance (7 Critical, 23 Auxiliary and 16 Potential), however 42 sites were data deficient i.e. there is insufficient data to determine their importance, however they could still be important sites. It is also recognised (Solent Recreation Mitigation Strategy 2017) that development in close proximity to bird sites can have a detrimental impact through increased disturbance both recreational and some acoustic and visual disturbance from construction activity. So, although a site may not overlap and directly impact an important bird site, it could have an indirect impact.
With regard to terrestrial development the Solent Waders and Brent Goose Strategy (2018) (SWBGS) should generally be the go-to document, developed with the specific intention to support decision makers on potential impacts to bird sites. The published SWBGS guidance provides a robust framework for considering the impacts and the level of mitigation/compensation required. Both the SWBGS and Solent Bird Studies have benefited from close collaboration, a shared dataset and a largely common analysis framework.
Strategic planning
There are tools and drivers within the current planning system in particular the National Planning Policy Framework (NPPF July 2018), for the protection of ecological sites and networks such as those identified by the Solent Bird Studies and SWBGS, but also for the positive allocation or development of strategic mitigation/compensation schemes. Pertinent paragraphs include;
170-Planning policies and decisions should contribute to and enhance the natural and local environment by:
d) minimising impacts on and providing net gains for biodiversity, including by establishing coherent ecological networks that are more resilient to current and future pressures;
174 -To protect and enhance biodiversity and geodiversity, plans should:
a) Identify, map and safeguard components of local wildlife-rich habitats and wider ecological networks, including the hierarchy of international, national and locally designated sites of importance for biodiversity; wildlife corridors and stepping stones that connect them; and areas identified by national and local partnerships for habitat management, enhancement, restoration or creation; and
b) promote the conservation, restoration and enhancement of priority habitats, ecological networks and the protection and recovery of priority species; and identify and pursue opportunities for securing measurable net gains for biodiversity.
The Solent Bird Studies provides an ideal model to both consider the impact of site allocations and develop district wide strategic mitigation schemes. In the formulation of local plans Local planning authorities should;
• use the Solent Bird Studies data as part of the appraisal process for potential sites
• Positively allocate key parts of the network and protect them from development
• Develop a strategic mitigation scheme to offset any impacts from local plan policies
• Include references to the protection of the network within Local Plan policies
Development control
The differences between the approach of the Solent Bird Studies and that of SWBGS, is that SWBGS has used an expanded set of categories to better reflect the intricacies of the terrestrial network and its alignment with planning procedures. However, they have also focused on sites outside of the SPA, so called functionally linked land, and therefore no information is presented on sites within the SPA. The reasons for this are entirely logical, the focus is on protecting sites that are not already protected by reason of being inside of the European site. It does however mean that important bird sites within the SPA, but in close proximity to proposed development may not be given the consideration they require. It is therefore considered that the Solent Bird Studies data should be used to flag sites that may be impacted, identify the need for further study, provide context of the importance and/or help determine appropriate mitigation.
Solent Bird Study data can be used to;
• Flag sites in close proximity to developments and at risk from construction and/or operational phase impacts
• Understand the local effect of impacts upon part of the important bird sites network
• Identify the need for further investigating e.g. data deficient sites
• Design mitigation strategies or determine appropriate sites for compensation.
7.4. Availability and use of data
It has always been the intention that Solent Birds Data is made freely available, including the raw bird data, spatial data and the statistical routines for processing and analysing the data. The data analysis was undertaken within the powerful and freely available statistics package/programming language R, which has the added benefit that the entire process can be captured within scripts and workspaces, enabling the analysis to be replicated. The data that will be made available will be;
• Tabular data of the observations recorded using the Solent Birds app
• GIS (poly lines) data of recorded birds movements
• GIS (polygon) layer of analysis results
• R scripts used in the analysis
All data and reports associated with the project can be downloaded from the Coastal Partners Website and the R-code, scripts and R workspace are available here https://github.com/jnightingale3/Solent-Bird-Studies But please do contact the project team on coastal.team@havant.gov.uk if you have any questions regarding accessing and using the data.
8. Next Steps
8.1. Taking
FCERM
schemes forward
One of the main drivers for undertaking the Solent Bird Studies was to establish a framework for addressing questions that need to be answered at the scheme level arising from the HRA of the North Solent SMP.
It is considered that the Solent Bird Study both in terms of the data and the methodology established for survey and analysis provides a robust dataset upon which to assess individual site importance and where sites are data deficient a model upon which to survey the site to gain the data to achieve a firm understanding of individual site importance.
The bird movement aspects have not been addressed at a strategic level and potentially the only method to obtain this strategic understanding is to undertake a large bird tagging study. However, while this strategic understanding would be useful it is not believed that it is essential at the scheme level. The vantage point methodology developed for this project, provides a robust model for understanding ‘local’ bird movement at the scheme level. Which will enable an understanding of how birds use the local network of individual sites.
Using both Solent Bird Study data and vantage point data provides a good understanding of both the relative importance of individual sites and how the bird population use them as a network. Therefore, a robust assessment of the implications of removing or modifying an existing site can be undertaken. This study has also reviewed and collated the available evidence on creating or recreating habitats and features used by birds and it is felt that in most cases the ecological function of a site can be protected and recreated through the scheme delivery.
Solent Bird Studies process for getting to a decision.
Part 1
Is there sufficient information on the likely effect on the network of sites used by roosting and inland feeding by SPA non-breeding (principally passage and over-wintering) bird populations.
Q1-Does the scheme have the potential to affect sites of importance (Solent Bird Studies (SBS)) for roosting or inland feeding over-wintering birds, using HRA process.
Yes-go to Q2
No- Proceed with standard consenting procedure.
Q2- Has the site/s been categorised as ‘critical’ or ‘auxiliary’ network or ‘potential’ under the SBS analysis.
Yes-go to Part 3
No-go to Q3
Q3- has the site been categorised as ‘no recorded use’ by the Solent Bird Studies analysis.
Yes- Proceed with standard consenting procedure.
No- go to Q4
Q4- has the site been categorised as ‘data deficient’ by the Solent Bird Studies analysis.
Yes- go to Part 2
No- investigation is required into the site’s status with regard its importance, why is the site not categorised and is it likely that the site has potential for importance, once completed return to Part 1.
Part 2
There is insufficient information on the relative importance of this area within the network of sites used by roosting and inland feeding by SPA non-breeding bird populations
Undertake site surveys in line with Solent Bird Studies/Solent Waders and Brent Goose Strategy methodology. Survey twice per month over high tide period from September to March for 3 years, rerun SBS analysis. Once complete return to Part 1
Part 3
There is information on the site’s relative importance for overwintering birds, but a greater understanding is required of the way birds use the site, e.g. linkages between intertidal feeding areas and the site and the degree of exchange of birds with other local roost sites within a high tide cycle.
Undertake bird movement study in accordance with SBS methodology. Survey twice per month over the rising tide period from September to March.
Undertake data analysis and assess the effect of this proposal on the functioning of the site and its surrounding network.
Figure 8.1- Flow chart of process of getting to a scheme level decision in relation to overwintering bird sites or network of sites using the Solent Bird Studies.
8.2. Future survey requirements
Vantage point surveys
Given the limitations described in Section 4, we found that the results produced by the vantage point method were not sufficiently detailed to provide a complete map of foraging catchment areas around roosts. Indeed the movements recorded were more typically between onshore areas as birds moved due to disturbance or the rising tide. Even using three surveyors intensively focused around a single estuary we were not able to get a complete picture of
which feeding areas were joined to which roosts, as the distance across the estuary (c. 6 km) is too far to see, let alone identify, birds, on top of which various landscape features such as trees and sea walls blocked inland sites from surveyors’ views (Figure 8.2).
8.2 Viewshed analysis depicting visible areas from each vantage point survey location (red dots). Areas visible to one surveyor only are blue, to two surveyors green, and visible to all surveyors pink; black areas would not be visible to any surveyors. Concentric yellow rings show 100m (inner) and 250m (outer) from the surveyor’s location, roughly corresponding to the distance over which most birds are identifiable to species by the naked eye and using handheld optics respectively.
We therefore propose that, instead of attempting an estuary- or larger-scale strategic overview, vantage point surveys are used at focal sites, for example those under consideration for development or inclusion in a FCERM or RHCP scheme. With a more intensely-focused survey effort a higher proportion of movements could be successfully recorded.
Combining these vantage point surveys with additional count data, perhaps collected by citizen scientists (Pocock et al., 2017) in order to bolster the sample size, ensures that the less disturbed sites are also included in the assessment. Moreover, an additional advantage of the focal-site approach is the reduction of disparities in relative disturbance across the surveyed sites.
For some surveys objectives, all waterbird species are of interest. Therefore, where volunteers are used, it can be stressed to them that specific identification is not necessary, as long as the flock recorded is of some waterbird and not some other species that occasionally uses
Figure
intertidal areas, such as feral pigeons, starlings or crows. This lowers the burden on volunteer surveyors skills, which may still be developing at the time of the survey.
Finally, the methods used here are in fact similar to the methods used to plan fieldwork to catch birds for a traditional bird-marking study (P. M. Potts, personal communication). Therefore, data from vantage-point surveys, which are comparatively cheap and rapid to gather, could be useful for planning bird-marking studies, or used in their place e.g. where access to a critical site cannot be granted.
Knowledge gaps
The Bird Movement Study reported here has identified flightpaths taken by birds between sites in the Solent SPAs and surrounding, non-SPA habitat. In conjunction with the Coastal Network Study, this information can be used to identify many of the most important locations for waterbirds with some confidence.
However, numerous questions remain unanswered about how protected species depend on different parts of the SPA network and surroundings, in particular several which would be crucial for developing a conservation strategy founded on site-based protection, mitigation and compensation.
8.2.2.1. What happens at night?
None of the data analysed in this study was collected at night. As over 50% of winter in England is after nightfall, it is crucial to ensure protection of areas used at night, without which birds may be unable to survive (Lourenço et al., 2008).
Previous studies have shown that waders use different areas at night for both feeding (Wood, 1986; Burton and Armitage, 2005) and roosting (Conklin and Colwell, 2007). Nocturnal roost sites may be fewer in number, and are more likely to be terrestrial rather than offshore (Conklin and Colwell, 2007); therefore they are more likely to be within the purview of this study than the diurnal roosts about which data is available. Conversely, birds forage over a wider area at night (Burton and Armitage, 2005), perhaps due to reduced territorial behaviour in the dark (Wood, 1986).
8.2.2.2. Foraging resources
Habitat requirements – how much area does an individual cover while foraging? As managed reserves and refuges form an integral part of the conservation strategy for waterbirds in the Solent, quantifying habitat requirements is necessary to ensure that adequate habitat is always available.
Dependence on terrestrial resources – Several species, such as Brent Geese and Curlew, use terrestrial resources to supplement marine feeding, in particular during high-tide periods (Tubbs and Tubbs, 1980; Inger et al., 2010). Individual birds have distinct feeding specialisations and patterns of site use (Durell, 2000), so records from terrestrial sites may represent a small number of terrestrial specialists, or it may be that most of the population depends in part on terrestrial resources. Confirming the proportion of individuals that feed terrestrially, and the proportion of their energy intake thus derived, is needed to determine how much terrestrial habitat needs protection in order to maintain the integrity of the Solent SPAs.
Tidal foraging – Available data from WeBS counts only covers the low-tide period; however, results from the Solent (de Potier, 2000, 2003) and elsewhere (van Gils et al., 2006) show that waterbirds move constantly during the tidal cycle as different areas become exposed. We currently lack any recent information on where birds forage in the middle of the tidal cycle.
8.2.2.3. Roost-site availability
Waders preferentially roost close to the area where they are foraging (Symonds et al., 1984; Dias et al., 2006). Roosts are frequently disturbed or rendered unavailable, for example by high tides, disturbance from people and predators or unfavourable weather conditions (Rogers et al., 2006; Rosa et al., 2006; Conklin and Colwell, 2007). When it is necessary to change roosts, they generally choose one of the closest alternatives (Pearce‐Higgins, 2001). Consequentially, the loss of a roost site can also reduce the area of feeding habitat which birds are able to use (Dias et al., 2006), resulting in population declines (Catry et al., 2011).
Roost catchments – Due to the lack of data on birds’ daily movements, and how individuals use the complex of potential roost sites around the Solent, it is impossible to predict with confidence the impacts of losing or damaging a roost. It is equally impossible to provide guidance on how far away replacement structures can be situated in cases where compensation is necessary (beyond, “as close as possible”).
Roost variability – Each individual likely depends on a network of possible roost sites (Pearce‐Higgins, 2001; Conklin and Colwell, 2007). Assessing how many sites an individual uses in the course of a winter will help to quantify the number of sites that should be available in a given management unit.
8.2.2.4. Estuary-scale movements and interchange between harbours
The Solent harbours are typically considered discreet units. For example, they are divided into four SPAs; one of those SPAs is subdivided into separate sites, Chichester and Langstone Harbours, for the BTO WeBS censuses, despite frequently-observed movements of birds between them (de Potier and Badley, 1999). Measuring the level of interchange between harbours and SPAs will facilitate verification that the current SPA subdivisions are appropriate for conserving these species. This will aid the upcoming JNCC review of the UK SPA network.
8.2.2.5. Juvenile settlement
Do juveniles use similar sites and habitats to adults? Do they use them in a similar way? Juvenile settlement processes, and recruitment to the local population, are essential for the maintenance or expansion of the Solent waterbird populations (Clark et al., 2004; Gunnarsson et al., 2012).
8.2.2.6. Uptake of new sites
Managed realignment, for example at Medmerry, provides a natural experiment to monitor how and when birds use newly-created habitat (Burton et al., 1996; Mander et al., 2013). This information would determine how far in advance compensatory habitat needs to be delivered before existing habitat is lost or degraded.
Future research
The most significant knowledge gaps identified in Section 8.2.2 relate to the behaviour of individuals over time. The present study provides a fairly comprehensive set of snapshots of the locations of bird flocks. However, as discussed above, the outstanding questions require knowledge of what individuals do. Therefore, future work to address these gaps should focus on individually marking and following birds.
To tackle the questions left unanswered by these studies, modern tags which automatically record, and in some cases remotely download, regular GPS-fixes of birds’ locations provide the most reliable means of gathering the requisite data (López-López, 2016).
Using only colour-rings may appear cheaper, as it is a cheaper marking technique. However, in order to achieve a useful level of spatial and temporal coverage – and especially to achieve the sought-after daily movements – a large number of skilled observers would be required to survey across the study area and throughout the tidal cycle, which would drastically increase costs. At the same time, colour-ring records are often less accurate than GPS data, are difficult to achieve at points a long distance from the shore, and basically impossible at night.
Therefore, colour-ringing projects should be considered a supplement to a detailed tagging study, to extend the range of species and time for which records can be gathered; however, exclusive use of that method would be incapable of addressing the remaining questions.
GPS tags can only be used on larger species; however, these tend to be the most mobile (Symonds et al., 1984; Rehfisch et al., 1996). Therefore, future research should aim to fit these tags to a large sample comprising several species. The knowledge gaps can then be plugged following the methods described below. It is however likely that with progressing technology that tags will be available for smaller species.
8.2.3.1. Habitat requirements: day and night
The totality of GPS fixes can be analysed to calculate kernel density estimates (Drake et al., 2001; Burton and Armitage, 2005; Choi et al., 2014). These are estimates of the area in which the individual spends a given proportion of its time – for instance, the area in which it spends 95% of its time is known as its ‘home range’, and where it spends 50% of its time is its ‘core area’ (Drake et al., 2001).
By including only data from outside high-tide periods, one obtains estimates of the area of habitat required to sustain each individual. Using techniques such as overlap analysis and rarefaction curves, it is then possible to extrapolate to calculate the area required by the entire designated population. Kernel density estimates are widely used in studies of waterbirds. These data could also be used to compare sites used by day and by night (Wood, 1986; Burton and Armitage, 2005).
8.2.3.2. Dependence on terrestrial resources
By comparing the amount of time spent foraging inland versus offshore, it is possible to estimate an individual’s relative dependence on each habitat type (Drake et al., 2001; Choi et al., 2014). The proportion of an individual’s diet derived from marine sources can also be calculated by drawing blood or feather samples (for example when catching to fit tags) and analysing stable isotope ratios (Inger et al., 2010).
8.2.3.3. Roost variability
For each individual, a complete record of locations at high-tide could be obtained. It would also be possible to compare the roost sites used during day and night (Conklin and Colwell, 2007). Comparison of the locations selected with tide-height records would also enable simulation of future sea-level rise scenarios, ensuring that the network of roost sites provided is robust to predicted future changes.
These data could be complemented by data from observations of colour-ringed individuals of other species, including historical data from projects run by the Farlington Ringing Group, by focussing on a number of known, key roosts and making systematic observations. This would ensure that the results obtained through tagging were applicable to other species, and represent patterns that are stable over a longer time.
8.2.3.4. Roosts: catchments, variability and nocturnal behaviour
During each tide cycle, each individual would be recorded moving from a roost site to a foraging area, providing a robust sample of daily movements and providing information about
how far birds will move. These data are particularly difficult to obtain through observations of colour-ringed birds.
An alternative approach for informing only the question of roost catchments is to dye birds plumage a bright colour after catching them at a focal roost, and subsequently resighting them while foraging (Dias et al., 2006). However, only two colours of plumage dye are available (Norton and Demopoulos, 2000), limiting the number of sites which could be studied, and birds marked in this way would not provide data for any of the other questions.
8.2.3.5. Movements between estuaries
The advantage of GPS tags is that, by continuously recording, they avoid any bias in survey effort. These data could therefore be used without correction to investigate the prevalence and frequency of movements between different estuaries or SPA units. However, given systematic survey coverage, or at least a record of survey effort and post-hoc correction of the data, colour-ring observations could also be used complementarily to address this question (e.g. Leyrer et al., 2006).
8.2.3.6. Juvenile settlement, recruitment and site-fidelity
To investigate juvenile settlement decisions and processes would require several years of fieldwork, marking individuals in the first year and observing them in subsequent years. Data from juveniles could then be compared with data from adults, giving a complete picture of inter-annual site-fidelity for each species (Inger et al., 2010).
GPS tags are typically severely limited in battery life (López-López, 2016), with a maximum lifespan of around a year. Therefore, questions involving multiple years of fieldwork may be better addressed using systematic colour-ring observations, especially from roost sites. Again newer technology in the future may ameliorate some of these factors
8.2.3.7. Uptake of new sites
As with studies of juvenile processes, studying the use of newly-created habitat areas or roosts would require multiple years of fieldwork, in order to capture the change in birds’ distributions before and after the new site became available. As discussed above, this type of question would be amenable to the use of colour-ring observations.
9. Conclusions
The project was developed as two separate but allied projects but has essentially been delivered as one combined project. The separation is however to some extent logical in presenting results The results of the two projects can to some extent be considered separately and indeed the relative success of the approaches used to answer the different questions has been different between the two projects.
9.1. Coastal Network Study
The approach for the coastal network study was based upon well tested methodologies and has been highly successful delivering a robust and repeatable dataset suitable for decision making.
All the records were submitted via the bespoke recording tools, www.solentbirds.org.uk and the SolentBirds app (for Android and iOS), utilising a citizen science approach, with 190 registered users resulting in 18,000 (and growing) records. The use of this system enabled near real time submission of records, avoided any data entry stage, minimised post processing requirements and avoided some of the pitfalls of crowd sourced/citizen science data collection. Namely the system constrained users to pre-selected options, free text input was minimised, and the familiar google maps interface allowed precise locational selection.
Another criticism of citizen science approaches is the quality of the data, compared to ‘professional’ observers and for some types of survey this may be a valid concern, however in this case the species options were deliberately limited to the most commonly occurring species and all records were verified by an experienced ornithologist, it is therefore not considered to have been detrimental to data quality.
The only major criticism of the approach is obtaining consistent geographical coverage and the submission of negative records, both matters have been issues for previous surveys such as the Solent Waders and Brent Goose Strategy. These issues are also allied, as volunteer birders tend to go to sites where they will see birds, so there are lots of records for known bird sites. In addition, volunteer birders tend not to record when they did not see birds, e.g. they visited a site and did not find birds. This has two consequences i) it is not clear if sites have been visited and no birds were found or if some areas have not been visited at all. ii) running statistics for frequency of visits and degrees of confidence in results is problematic. It was attempted to overcome this shortcoming using a small team of ‘super volunteers’ and project staff to fill data gaps and it is felt this was successful in achieving greater robustness in the data for some areas, but gaining consistent geographical coverage across the entire project area with paid surveyors would have been prohibitively expensive, and as discussed in greater detail below there is a limitation in the availability of suitable surveyors. The use of sightings of gull species as a proxy for negative records also helped ameliorate this effect. It is also our expert opinion that although technically birds using areas could have been missed, due to the generally good coverage of birders in the Solent it is unlikely that any regularly used sites have not been recorded. It is therefore believed that the Coastal Network Study represents best available evidence on the relative importance of waders’ roost and inland feeding areas in the Solent.
The key objectives in the original project specifications to be met in order to achieve the aim of the coastal network study are to:
1. Improve knowledge of high tide roost sites within the Solent that are critical to supporting roosting and feeding wildfowl and waders (integral links to a network of sites).
2. Agree mitigation and compensation options that maintain the Solent wide network of environmental sites for wildfowl and waders, enabling delivery of coastal change and FCERM schemes (i.e. if we lose current bird roosting sites to managed realignment, where can we create new bird roosting sites, with absolute confidence that they will effectively compensate / mitigate losses, and be acceptable to regulators and stakeholders);
3. Develop informed advice for future generation SMPs and FCERM strategies and confirmation of longer-term policy;
4. Develop informed advice for the delivery of the Regional Habitat Compensation Programme (RHCP) and FCERM schemes, which improve the environment and protect our communities. The RHCP is the Government's approved strategic compensation mechanism for addressing habitat losses arising from FCERM;
5. Create a spatial tool for education, engagement and decision making;
6. Develop a strategy for the protection of key sites via Local Authority Local Plans and informed advice towards future development that could bring significant contributions towards match funding Flood Defence Grant in Aid (FDGiA).
7. Produce a comprehensive final written report for presentation and justification of outputs within the spatial tool.
The study has improved our knowledge of the locations supporting roosting and feeding waders and wildfowl within the Solent and has developed a robust methodology to collate and compare that information for future schemes. It is however recognised that importance varies with time due to habitat and land-use changes in that location or local network, changes in bird populations and changes in human behaviour principally recreation patterns. So it is essential that future schemes are preceded by a series of robust surveys and assessments using the coastal network methodology in order to asses there potential impact +/- VE on Solent waders and wildfowl.
Gaining an understanding of the network at a strategic level whilst valid, was time limited in terms of understanding the potential impact at a scheme level. It is also clear that maintaining an adequate network is essential at a range of spatial scales and this is an objective that is delivered through the work of the Solent Waders and Brent Goose Strategy which uses a slightly modified version of the Solent Bird Studies metrics to categorise site importance. This study provides a mechanism to assess the relative importance of a site within a network and allied to the bird movement study elements of how it works with that network. However, it also identifies that understanding the compensation and mitigation requirements is best addressed at a scheme level due to the complexities of how birds use sites and the change in this use over time.
This study provides a solid underpinning for understanding the importance of roosting and inland feeding areas within the Solent and how to assess impacts for future FCERM and habitat creation schemes going forward. Understanding how to assess impacts, provision of baseline data and a commitment to updating site data, should provide confidence that strategies including FCERM, habitat creation and other land-use can be adequately mitigated or compensated in the future. Indeed, the findings and methodologies of this study have already been used in assessing impacts on a range of FCERM and habitat creation schemes, FCERM strategies and local plan developments.
With the rapid development in information technology and potential obsolescence of specific spatial technologies. The main spatial output from the study is a GIS layer in a standard and highly transferrable format (ESRI Shapefile) that can and had been shared widely. This GIS layer provides the context and a framework for assessing schemes and strategies going forward. The data has been shared with the various county recorders and with SWBGS. The metrics developed to assess new data is also available and in a slightly modified form is being used by SWBGS to classify and update site information as new data is received. For people with desire and skills the R (an open source statistical scripting tool) scripts that can be used to collate, clean, transform and undertake the various analysis are available to download, use and modify as necessary.
9.2. Bird Movement Study
The key objectives to be met in order to achieve this aim are to:
1. Baseline our current understanding of bird movements within the Solent and improve our knowledge of links between feeding and roost sites for different bird species.
2. Establish additional data requirements to develop and confirm our current understanding of bird movements within the Solent. This is achieved via communications with stakeholders including environmental regulators, operating authorities and decision makers to ensure the correct level of data is collected in order to allow coastal change FCERM decisions to be made.
3. Implement measures for capturing this information through the development of guidance and new data collection techniques.
4. Discuss with regulators, operating authorities and decision makers and agree on a scientific basis across the Solent that will enable delivery of future FCERM, through decisions that maintain the Natura 2000 network of sites while allowing schemes to be delivered on the ground.
The need to understand how birds use the network and what linkages there are between feeding and roosting locations is important to understand the implications of making changes to the coastal environment. There is, however, not an established methodology for undertaking bird movement studies, therefore considerable research was undertaken to establish a suitable approach. Various methods ranging from direct observation, radar tracking and marking individual birds has been considered. Marking individual birds with devices capable of recording GPS level locational data and enabling remote recovery of data has obvious advantages for this type of question, enabling 24 hour, all weather recording of data, record areas not observable from viewpoints and allowing the tracking of individuals. However current limitations in the technology restrict the species that can be marked, and/or creates trade-offs between frequency of positional fixes and duration of deployment. In addition the availability of the expertise able to undertake captures is very limited and the ability to catch a representational sample of a number of species across a representational geographic extent is not a trivial matter. Lastly the cost, in order to tag a sample large enough over multiple years to understand local movements of birds, even if achievable is prohibitively expensive.
A methodology of vantage point counts has been developed and tested at three scales (scheme/site, whole estuary and multiple estuary) for this study. There are significant limitations in the approach at all scales; i) a four hour survey is a long time for human observers but only 16% of the day, ii) observations can generally be made in daylight only, iii) adverse weather limits observer efficacy, iv) observing birds at an individual level (particularly between surveys) is difficult/impossible. In addition at the larger geographic scales; organisation, co-
ordination and availability of observers is a serious limitation. However, the vantage point survey at an appropriate scale undertaken by experienced observers can provide a good picture of local bird movements, can identify linkages between feeding and roosting areas and observe the effect of weather and disturbance on the use of different areas. Which are exactly the answers required at the scheme level. It is therefore considered that the vantage point approach at an appropriate scale represents a cost effective, repeatable and robust methodology that can be utilised at the scheme level and will provide adequate understanding to take schemes forward.
Undertaking the bird movement aspects at the scheme level however does not provide the strategic overview of bird movement that would have been useful in setting the context at the scheme level and also to better understand how it can influence SPA site integrity. But it should be remembered that, as originally envisaged, the study was only going to research the effectiveness of using existing bird ringing and WeBS data, therefore the development and testing of an approach is a significant step-forward. It is considered that sufficient understanding can be gained through the scheme level approach, it is further considered that the utility of understanding the strategic context is not unique to FCERM schemes, but also land-use planning and monitoring the integrity of the SPA network. It is considered that, whilst not essential for taking schemes forward, gaining this strategic context would be highly valuable. Using some form of GPS marking of individual birds is currently the only way to achieve this, notwithstanding the limitations discussed above, sharing the cost between the different applications for the data may make the cost more feasible. All the time the costs and size of the technology is reducing and may also make projects more cost effective.
9.3. Network analysis
The fragmented nature of Solent coastal habitats means that habitat loss cannot be treated simply as the loss of a given area, as it could be in a more contiguous environment; rather, sites need to be considered in the context of their surroundings, distance to other resources and the connections between them.
Network analysis has previously been used at a regional scale to look at the importance of e.g. migratory stopover sites or a series of protected areas. Analysing local-scale movements as connections between a network of independent sites is an approach developed specifically for the Solent Bird Studies, using statistical techniques developed for other purposes.
These techniques provide a robust interpretation of the data supplied; however, if the input data is incomplete the resulting network will be too. Network analysis is a flexible approach that can be used with a variety of data sources, including also colour-ring and smart-tag datasets. As studies of bird movements in the Solent continue, this approach can be used to provide a richer, more complete and more detailed understanding of the Solent site network.
9.4. Recommendations and future work
Coastal network study
• The methodology for individual site evaluations and data derived from it should be accepted as best available evidence. The data and analysis method has been largely shared with SWBGS.
• It will be necessary to keep this data up to date, through collating records and maintaining a level of survey effort.
• As noted, this data and a need to maintain the data shared is common to a number of initiatives including SWBGS, Bird Aware Solent and SSSI/N2K condition monitoring e.g. Common Standards Monitoring. It would be prudent to maintain a grouping to ensure this collaboration continues. It is expensive to collect and maintain data and it is always better to collect data correctly once and use it for multiple purposes.
• Allied to the above it is noted that a number of initiatives undertake coastal bird surveys; e.g. WeBS, SWBGS, LPA/HBIC, Bird Aware Solent and site wardens, collaboration on data collection could enable the more effective sharing of this survey effort and the subsequent data.
• The development of the app and website was a considerable investment by the project and it has been and indeed still is highly valuable resource for data collection. It is recommended that the resource is maintained and improved. It would appear to be a good fit with the grouping of common data users noted above to take this forward.
Bird movement study
• The methodology for undertaking vantage point surveys should be adopted as a mechanism for gaining adequate information at the scheme level. The appropriate scale is considered to be an area that can be covered by 2-3 observers at one time, which will vary dependant on the topography of an area. This is a good compromise between covering a wide enough area, whilst maintaining consistency, robustness and achievability.
• That the network analysis approach is adopted for subsequent analysis of bird movement data and the derived metrics are used to add value to the coastal network study data.
• That a network of volunteers is maintained and supported to ensure future projects have sufficient experienced surveyors to assist with data collections. This could include training and accreditation of volunteers.
• Should funding become available a bird tagging study using GPS tags should be undertaken to gain a strategic understanding of birds’ movement in the Solent. It is also noted that there is a serious limitation in the number of people and indeed the demographic of individuals with the skills and qualifications to undertake bird catches.
Overall
• Due to the large number of organisations involved, turnover of key personnel and the increasing importance of transparency in both the policy and science arenas, care should be taken to develop and maintain a more adequate system to collate, store and distribute Solent bird data, along with appropriate metadata (survey protocols, funding organisations, organisers, known problems with the data, etc.). The SolentBirds database could be one such repository, along with regular backups in a non-volatile repository such as figshare or dryad (Whitlock, 2011; British Ecological Society, 2014).
• Linkages between the findings of this project and the delivery of the Regional Habitat Compensation Programme should be investigated and developed. Data from the Solent Bird Studies has already fed into site assessments for the RHCP Tactical phase work to prioritise the delivery of intertidal habitat creation sites. The recommendations of this report will be used to inform the scheme level assessments and design of habitat
compensation sites to ensure they provide the maximum benefit to the Solent SPA network.
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11.2. APPENDIX B: Site qualification information for Solent SPAs and Ramsar sites
This site qualifies under Article 4.2 of the Birds Directive by supporting over winter populations of European importance of migratory species.
Migratory Species Over Winter
Dark-bellied Brent Goose Branta bernicla bernicla, 2,290 individuals representing 1.3% of the north-west European population and 2.5% of the British wintering population (5 year peak mean 1986/87 – 1990/91).
Dunlin Calidris alpina alpina, 8,010 individuals representing at least 1% of the population in Great Britain (5 year peak mean 1986/87 – 1990/91).
Black Tailed Godwit Limosa limosa islandica, 70 individuals representing greater than 1% of the population in Great Britain (5 year peak mean 1986/87 – 1990/91).
Red Breasted Merganser Mergus serrator, 100 individuals representing 1% of the population in Great Britain (5 year peak mean 1986/87 – 1990/91).
Ramsar Criterion 3 –wetland supporting important plant and/or animal species
The intertidal mudflat areas possess extensive beds of eelgrass Zostera angustifolia 1 and Zostera noltei which support the grazing dark-bellied Brent geese populations. The mud-snail Hydrobia ulvae is found at extremely high densities, which helps to support the wading bird interest of the site.
Common cord-grass Spartina anglica dominates large areas of the saltmarsh and there are also extensive areas of green algae and
1 It is now widely accepted in the UK that Zostera angustifolia is a phenotypic variant of Zostera marina but at the time of Ramsar site designation it was considered a separate species and the original qualifying criteria have been included here.
Table A.9.1 Portsmouth Harbour SPA site qualification information (from Natural England Conservation Advice, December 2015)
Table A.9.2 Portsmouth Harbour Ramsar site qualification information (from Ramsar Information Sheet, JNCC, February 1995)
Ramsar Criterion 6Species/populations occurring at levels of international importance.
sea lettuce. More locally the saltmarsh is dominated by sea purslane Halimione portulacoides which gradates to more varied communities at the higher shore levels. The site also includes a number of saline lagoons hosting nationally important species.
Qualifying species / populations (as identified at designation)
Number of individuals (5 year peak mean 1998/9-2002/3)
2,105 individuals, representing an average of 2.1% of the GB population
The Portsmouth Harbour Ramsar site also supports fauna and flora currently occurring at levels of national importance shown in Table B.10
Table A.9.3 Species of national importance present in Portsmouth Harbour Ramsar site (from Ramsar Information Sheet, JNCC, February 1995)
Species currently occurring at levels of national importance
Spring/autumn
Little egret Egretta garzetta
Black-tailed godwit Limosa limosa islandica
Peak counts (5 year peak mean 1998/9 - 2002/3)
47 individuals, representing an average of 2.8% of the GB population
343 individuals, representing an average of 2.2% of the GB population
Higher Plants, including Zostera noltei, Zostera angustifolia, Zostera marina and Inula crithmoides
Table A.9.4 Chichester and Langstone Harbours SPA site qualification information (from Natural England draft Conservation Advice, September 2017)
Site qualification criteria
This site qualifies under Article 4.1 of the Birds Directive by supporting populations of European importance of species listed on Annex I of the Directive
Qualifying details
During the breeding season the area regularly supports (5 year mean 1982 – 1986)
Little tern, Sterna albifrons - 109 pairs representing up to 5.7% of the UK breeding population (5 year mean 1982 – 1986)
Common tern, Sterna hirundo - 126 pairs representing up to 1.1% of the UK breeding population (5 year mean 1982 – 1986)
Site qualification criteria
Qualifying details
Sandwich tern, Sterna sandvicensis - 93 pairs representing up to 0.7% of the UK breeding population (5 year mean 2011 - 2015).
Over Winter the area regularly supports (5 year peak mean 1982/83 - 1986/87 unless stated otherwise). Internationally important population percentages are taken from the original SPA citation.
Bar-tailed godwit, Limosa lapponica – 1,491 individuals representing up to 3.9% of the GB breeding population
This site also qualifies under Article 4.2 of the Directive (79/409/EEC).
Over winter the area regularly supports:
Northern pintail, Anas acuta – 323 individuals representing 1.1% of the GB population
Northern shoveler, Anas clypeata – 124 individuals representing 0.7% of the GB population
Eurasian teal, Anas crecca – 2,553 individuals representing 1% of the North-western Europe population
Eurasian wigeon, Anas penelope – 3,947 individuals representing 0.9% of the GB population (5 year peak mean 2010/11 – 2014/15)
Ruddy Turnstone, Arenaria interpres – 564 individuals representing 1.2% of the GB population
Dark-bellied Brent Goose, Branta bernicla bernicla –17,712 individuals representing 12% of the Western Siberia/Western Europe population
Sanderling, Calidris alba – 407 individuals representing 3.1% of the Eastern Atlantic/Western & Southern Africa wintering population
Dunlin, Calidris alpina alpina – 53,977 individuals representing 2.6% of the Northern Siberia/Europe/Western Africa population
Common Ringed Plover, Charadrius hiaticula – 1,012 individuals representing 3% of the GB population
Red-breasted merganser, Mergus serrator – 366 individuals representing 4.4% of the GB population (5 year peak mean 2010/11 – 2014/15)
Eurasian Curlew, Numenius arquata – 2,937 individuals representing 2.1% of the GB population
Site qualification criteria
Qualifying details
Grey Plover, Pluvialis squatarola – 3,271 individuals representing 3.9% of the Eastern Atlantic wintering population
Common Shelduck, Tadorna tadorna – 4,287 individuals representing 4% of the North-western Europe population
Common Redshank, Tringa totanus – 3,417 individuals representing 1.4% of the Eastern Atlantic wintering population
The area qualifies under Article 4.2 of the Birds Directive by regularly supporting at least 20,000 waterfowl.
Over winter, the area regularly supports 108,811 individual waterbirds including: Wigeon Anas penelope, Bar-tailed Godwit Limosa lapponica, Dark-bellied Brent Goose Branta bernicla bernicla, Common Ringed Plover charadrius hiaticula, Grey Plover Pluvialis squatarola, Dunlin Calidris alpina alpina, Redshank Tringa totanus, Shelduck Tadorna tadorna, Curlew Numenius arquata, Teal Anas crecca, Pintail Anas acuta, Shoveler Anas clypeata, Red-breasted Merganser Mergus serrator, Ruddy turnstone Arenaria interpres, Sanderling Calidris alba
Table A.9.5 Chichester and Langstone Harbours Ramsar site qualification information (from Ramsar Information Sheet, JNCC, October 1987)
Ramsar Criterion
Ramsar criterion 1 – a representative, rare, or unique example of a natural or near-natural wetland type
Ramsar criterion 5 –regularly supports 20,000 or more water birds
Ramsar criterion 6 – species / populations occurring at levels of international importance
Two large estuarine basins linked by the channel which divides Hayling Island from the main Hampshire coastline. The site includes intertidal mudflats, saltmarsh, sand and shingle spits and sand dunes.
Assemblages of international importance:
Species with peak counts in winter: 76,480 waterfowl (5 year peak mean 1998/99 - 2002/2003)
Qualifying species / populations occurring at levels of international importance
Number of individuals (5 year peak mean 1998/9 - 2002/3)
853 individuals, representing an average of 1.1% of the population
906 individuals, representing an average of 2.5% of the population
2,577 individuals, representing an average of 1% of the population
12,987 individuals, representing an average of 6% of the population
1,468 individuals, representing an average of 1.8% of the GB population
3,043 individuals, representing an average of 1.2% of the population
33,436 individuals, representing an average of 2.5% of the population
During the breeding season (species identified for possible future consideration under criterion 6)
Little tern, Sterna albifrons albifrons
130 apparently occupied nests, representing an average of 1.1% of the breeding population (Seabird 2000 Census)
The Chichester and Langstone Harbours Ramsar site also supports fauna and flora currently occurring at levels of national importance shown in Table B.13
Table A.9.6 Species of national importance present in Chichester and Langstone Harbours Ramsar site (from Ramsar Information Sheet, JNCC, October 1987)
Species currently occurring at levels of national importance
During the breeding season (Seabird 2000 Census)
Mediterranean gull Larus melanocephalus 47 apparently occupied nests, representing an average of 43.5% of the GB population
Black-headed gull Larus ridibundus 3,180 apparently occupied nests, representing an average of 2.4% of the GB population
Common tern Sterna hirundo hirundo 127 apparently occupied nests, representing an average of 1.2% of the GB population
Species currently occurring at levels of national importance
Spring/autumn
Little egret
Eurasian oystercatcher
Peak counts (5 year peak mean 1998/92002/3)
224 individuals, representing an average of 13.5% of the GB population
3,403 individuals, representing an average of 1% of the GB population
Whimbrel Numenius phaeopus, 192 individuals, representing an average of 6.4% of the GB population
Eurasian curlew Numenius arquata arquata
3,108 individuals, representing an average of 2.1% of the GB population
Spotted redshank Tringa erythropus 6 individuals, representing an average of 4.4% of the GB population
Common greenshank Tringa nebularia
Ruddy turnstone ,Arenaria interpres interpres
215 individuals, representing an average of 36% of the GB population
569 individuals, representing an average of 1.1% of the GB population
Winter Peak counts (5 year peak mean 1998/9- 2002/3)
Table A.9.7 Solent and Southampton Water SPA site qualification information (from Natural England draft Conservation Advice, September 2017)
Site qualification criteria
This site qualifies under Article 4.1 of the Birds Directive by supporting populations of
Qualifying details
During the breeding season the area regularly supports
European importance of species listed on Annex I of the Directive
This site also qualifies under Article 4.2 of the Directive (79/409/EEC). Over winter the area regularly supports:
Little tern, Sterna albifrons - 49 pairs representing 2% of the GB breeding population (5 year mean, 1993-1997)
Common tern, Sterna hirundo - 267 pairs representing 2.2% of the GB breeding population (5 year mean, 1993-1997).
Sandwich tern, Sterna sandvicensis - 231 pairs representing 1.7% of the GB breeding population (5 year mean, 1993-1997).
Roseate tern, Sterna dougallii – 2 pairs representing 3.1% of the GB breeding population (5 year mean, 1993 – 1997)
Mediterranean gull, Larus melanocephalus – 2 pairs representing up to 13.9% of the GB breeding population (5 year mean 1994 – 1998)
Over Winter the area regularly supports
Dark-bellied Brent Goose, Branta bernicla bernicla – 7,506 individuals representing 2.5% of the Western Siberia/Western Europe population (5 year peak mean 1992/93 – 1996/97).
Black-tailed godwit, Limosa limosa islandica – 1,125 individuals representing 1.7% of the Iceland – breeding population (5 year peak mean 1992/93 – 1996/97)
Eurasian teal, Anas crecca – 4,400 individuals representing 1.1% of the Northwestern Europe population (5 year peak mean 1992/93 – 1996/97).
Common Ringed Plover, Charadrius hiaticula – 552 individuals representing 1.2% of the Europe/Northern Africa –wintering population (5 year peak mean 1992/93 – 1996/97).
The area qualifies under Article 4.2 of the Birds Directive by regularly supporting at least 20,000 waterfowl.
Over winter, the area regularly supports 51,361 individual waterfowl (5 year peak mean 1991/92 – 1995/96) including:
Dark-bellied Brent Goose Branta bernicla bernicla, Common Ringed Plover charadrius hiaticula, Teal Anas crecca, Black-tailed godwit Limosa limosa islandica
Table A.9.8 Solent and Southampton Water Ramsar site qualification information (from Ramsar Information Sheet, JNCC, October 1998)
Ramsar Criterion
Ramsar criterion 1 – a representative, rare, or
Qualifying details
The site is one of the few major sheltered channels between a substantial island and mainland in European waters, exhibiting
Ramsar Criterion Qualifying details
unique example of a natural or near-natural wetland type
Ramsar criterion 2supports vulnerable, endangered, or critically endangered species or threatened ecological communities
Ramsar criterion 5 –regularly supports 20,000 or more water birds
Ramsar criterion 6 – species / populations occurring at levels of international importance
an unusual strong double tidal flow and has long periods of slack water at high and low tide. It includes many wetland habitats characteristic of the biogeographic region: saline lagoons, saltmarshes, estuaries, intertidal flats, shallow coastal waters, grazing marshes, reedbeds, coastal woodland and rocky boulder reefs.
The site supports an important assemblage of rare plants and invertebrates. At least 33 British Red Data Book invertebrates and at least eight British Red Data Book plants are represented on site.
Assemblages of international importance:
Species with peak counts in winter: 51,343 waterfowl (5 year peak mean 1998/99-2002/2003)
Table A.9.10 Pagham Harbour SPA site qualification information (from Natural England Conservation Advice, March 2017)
Site qualification criteria
This site qualifies under Article 4.1 of the Birds Directive by supporting populations of European importance of species listed on Annex I of the Directive
Qualifying details
During the breeding season the area regularly supports
Little tern, Sterna albifrons – there is no abundance value on the original SPA citation but the site currently supports 14 breeding pairs, representing 0.7% of the GB breeding population (5 year mean 2012-2016).
Common tern, Sterna hirundo – there is no abundance value on the original SPA citation but the site currently supports 14 breeding pairs representing 0.14% of the GB breeding population (5 year mean 2012-2016).
Over Winter the area regularly supports
Ruff, Philomachus pugnax - 160 individuals representing 10% of the GB wintering population (5 year peak mean, 1980/1981 to 1985/1986).
This site also qualifies under Article 4.2 of the Directive (79/409/EEC).
Over winter the area regularly supports:
Dark-bellied Brent Goose, Branta bernicla bernicla –3,045 individuals, representing 2% of the European Wintering population (5 year peak mean 1980/1981 to 1985/1986).
Table A.9.11 Pagham Harbour Ramsar site qualification information (from Ramsar Information Sheet, JNCC, March 1988)
Ramsar criterion Qualifying details
Ramsar Criterion 6Species/populations occurring at levels of international importance.
Qualifying species / populations (as identified at designation)
Number of individuals (5 year peak mean 1998/9 - 2002/3)
