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West Area Recorder: Colin Jakes, 7 Maltward Avenue, BURY ST. EDMUNDS, IP33 3XN Tel: 01284 702215

North-East Area Recorder: Richard Waiden, 21 Kilbrack, BECCLES NR349SH Tel: 01502 713521

South-East Area Recorder: Brian Thompson, 42 Dover Road, IPSWICH IP3 8JQ Tel: 01473 726771 Lowwtoft

Orfordntss I Havergaie Island StrMt

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SUFFOLK BIRDS VOL. 46 Incorporating a review of birds in Suffolk in 1996

Editor M D Crewe Photographic and Artwork Editor T P Kerridge

Published by SUFFOLK N A T U R A L I S T S ' SOCIETY 1998 1


Published by T h e S u f f o l k Naturalists' Society, c/o T h e M u s e u m , H i g h Street, Ipswich IP1 3 Q H Š T h e S u f f o l k Naturalists' Society 1998 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior permission of the Copyright owners.

T h e S N S is a Registered Charity No. 2 0 6 0 8 4

ISSN 0 2 6 4 - 5 7 9 3

Printed by H e a l e y s Printers Ltd. 4 9 - 5 5 Fore Street, S u f f o l k IP4 1JL 2


CONTENTS Page Editorial Mike Crewe The Changing Fortunes of the Red Kite in Suffolk lan Carter Sawbill Movements at Landguard Point, Suffolk, 1983-96 Nigel Odin Seabird Movements and Abundance off Covehithe, Suffolk, 1994-96 1. Fulmar, Gannet, Kittiwake, Guillemot and Razorbill Peter Dare Movements and Abundance of divers off Covehithe, Suffolk, 1994-96 Peter Dare The 1996 Suffolk Bird Report: Introduction Systematic List Appendix I: Category D species Appendix II: Escapees Appendix III: List of non-accepted records List of Contributors Gazetteer Earliest and latest dates of summer migrants Notes: Night migrants over Felixstowe Mike Crewe Collared Dove raping Turtle Dove Jean Garrod Rarities in Suffolk in 1996: Collared Pratincole Brian Small Arctic Warbler John Archer Booted Warbler Dave Jupp Crested Lark Paul Holmes Rustic Bunting Ricky Fairhead Western Bonelli's Warbler Mark Grantham A Guide to Recording Birds in Suffolk Landguard Bird Observatory, 1996 Michael James Suffolk Ringing Report Tony Hurrell & Mike Marsh

5 6 11 16 37 48 48 50 161 162 163 165 167 169 170 170 170 171 171 171 172 173 174 175 177 179 186

List of Colour Illustrations Facing Plate Page No. 14. Great Spotted Woodpecker 97 Stan Dumican 120 15. Crested Lark Robin Chittenden 120 16. Short-eared Owl Alan Tate 121 17. Black Redstart Robin Chittenden 121 18. Song Thrush Alan Tate 144 19. Whitethroat Alan Tate 144 20. Reed Warbler Alan Tate 145 21. Western Bonelli's Warbler Alan Tate 145 22. Booted Warbler Alan Tate 168 23. Arctic Redpoll Derek Marsh 168 24. Brambling Stan Dumican 169 25. Waxwings Alan Tate 169 26. Greenshank Robin Chittenden

Plate Facing No. Page 1. Lakenheath Fen reserve Mike Crewe 48 2. Red Kite chick lan Carter 48 48 3. Red Kite chick lan Carter 4. Slavonian Grebes Andrew Easton 49 5. Black-necked Grebe Alan Tate 49 72 6. Eiders Andrew Easton 7. Lapwing Robin Chittenden 72 8. Curlew Sandpiper Alan Tate 73 73 9. Black-tailed Godwit Alan Tate 10. Kittiwake Robin Chittenden 96 11. White-winged Black Tem 96 Robin Chittenden 12. Lesser Black-backed Gull Andrew Easton 96 97 13. Bam Owl Stan Dumican

The copyright remains (hat of the photographers.

3


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Notice to Contributors Suffolk Birds is an annual publication of records, notes and papers on all aspects of Suffolk ornithology. Except for records and field descriptions submitted through the county recorders, all material should be original. It should not have been published elsewhere or offered complete or in part to any other journal. Authors should carefully study this issue and follow the style of presentation, especially in relation to references and tables. Where relevant, nomenclature (English and scientific) and order should follow Dr K. H. Voous's List of Recent Holarctic Bird Species. If typed, manuscripts should be double-spaced, with wide margins, on one side of the paper only. They must be in the final form for publication: proofs of longer papers are returned to authors, but alterations must be confined to corrections of printer's errors. The cost of any other alterations may be charged to the author. It is possible for papers to be submitted on computer disk; contact the Editor initially for advice. Photographs and line drawings are required to complement each issue. Suitable photographs of birds, preferably taken in Suffolk, should ideally be in the form of 35mm transparencies. A payment of ÂŁ10 will be made to the photographer for each photograph published and ÂŁ5 for each drawing. Every possible effort will be made to take care of the original photographs and artwork. However, photographers and artists are reminded that neither the Editor nor the SNS can be held responsible in the unlikely event that loss or damage occur. Authors may wish to illustrate their papers, but this will be subject to the illustrations being of the standard required by the Editor and the decision on such matters will rest with him. Material submitted for publication should be sent to the Editor no later than March 1st of each year. Authors of main papers may request up to five free copies of the journal. Suffolk Ornithological Records Committee: Chair: John Cawston Area County Recorders: Colin Jakes, Richard Waiden, Brian Thompson Secretary: David Walsh Other Committee Members: Ricky Fairhead, Trevor Kerridge, Stuart Ling, Gary Lowe, Mike Marsh, Derek Moore, David Pearson, Steve Piotrowski, Richard Rafe, Malcolm Wright. ADDRESSES Papers, notes, drawings and photographs: The Editor ( S u f f o l k Birds), The Suffolk Naturalists' Society, c/o The Museum. High Street, Ipswich IP1 3QH. Records: See inside front cover. Suffolk Ornithological Records Committee - correspondence: The Secretary, SORC, c/o The Museum, High Street, Ipswich IP1 3QH.

4


EDITORIAL Just a quick Editorial this year to save on space! It seems that Sujfolk Birds is becoming a victim of its own success; with production and distribution costs everincreasing and an ever-growing number of records to be included in the systematic list, it gets more and more difficult each year to reach a balance between producing a report that is as thorough and complete a record as possible, whilst remaining a sensible size (and consequently a sensible price!). This year, dĂŠcisions have had to be made as to what to include and what to leave out from the report. I firmly believe that the systematic list needs to be as complete and accurate as possible. Thus we do not want to leave out any record that we (perhaps a little arbitrarily) consider important. The list remains an important historical record of the state of the County's birds during any one year and should therefore not be compromised. One way to save space would be to cut down on the number of other articles that appear in the report. But this is where the conflict arises; surely bird reports are more than just a systematic list? To me the value of a County report as a place to publish papers on a wide range of ornithological matters should not be underestimated, and this year's papers by Peter Dare and Ian Carter are testimony to this. In the end, I have had to cut down on the amount of artwork as a way of saving space. This is a shame as we are spoilt for bird artists in the County and their work has enhanced Sujfolk Birds for many years. Hopefully we can increase the amount of artwork again next year and stili include an excellent range of papers as well as a thorough systematic list. Sharp eyes will notice that, regrettably, I have had to omit the BTO/JNCC/RSPB Breeding Bird Survey results. Whilst this is a shame - as the intention is for this to be an annual feature in Sujfolk Birds - we do at least have the opportunity to produce two years' worth of data in the next issue. This will give more time to assess the results in a countywide context and to see how Suffolk compares with the national picture. On a personal note, I have to say that I would stili like to see many more BBS squares covered in Suffolk. I stili feel that not enough concern has entered the minds of the pager-toting, listing fraternity over the decline in our breeding birds - perhaps once they need a 'stake-out' to tick Song Thrush, Yellowhammer or even Skylark for the year (as is already the case, for example, with Redpoll, Tree Sparrow, Corn Bunting and Bullfinch) they will wake up and set aside a mere handful of hours a year to partake. Finally, a grateful acknowledgement for the help of Philip Murphy, Mike Marsh and Nigel Odin, without whose assistance there would not have been a Sujfolk Birds this year.

5


The Changing Fortunes of the Red Kite in Suffolk Ian Carter, English

Nature

Introduction The Red Kite was formerly a common and widespread bird within Britain and even occurred in some of our larger towns and cities. From Tudor times onwards, in common with many other species of bird of prey and predatory mammal thought to threaten domestic livestock and gamebirds, it was heavily persecuted. This was even encouraged by Acts of Parliament offering generous bounties for each kite head and had an increasing impact on kite numbers, particularly with the development of ever more effective methods of control. By the end of the 19th century, as a result of continuous shooting, trapping and poisoning, the Red Kite was extinct as a breeding bird in England and Scotland and reduced to only a handful of pairs in remote parts of central Wales. The last recorded breeding in Suffolk was near Bures in about 1835 (Holloway 1996). Current status In recent times the fortunes of the Red Kite in Britain have greatly improved thanks to the continuing and increasingly rapid recovery of the population in Wales (127 pairs in 1996) and the well publicised reintroduction programme. Work to reintroduce kites in England and Scotland began in 1989, funded by the Nature Conservancy Council (and later the Joint Nature Conservation Committee) and the RSPB, and has resulted in the establishment of two small breeding populations. In 1996 at least 35 breeding pairs fledged 80 young in southern England and 16 breeding pairs fledged 38 young in northern Scotland. Work, funded by English Nature, Scottish Natural Heritage and the RSPB, has now started at new sites in the English Midlands and central Scotland with the objective of establishing two further breeding populations (Carter et al. 1995). Despite these improvements, the Red Kite currently occupies only a tiny fraction of suitable habitat within Britain and in most areas is still only a rare visitor. Status of the Red Kite in Suffolk The Red Kite is mainly a scarce winter visitor and passage migrant in Suffolk although the number of records has been steadily increasing in recent decades. The increase is shown by the following table from Suffolk Birds 1990, summarising records of Red Kites since the 1950s, and presumably reflects the improving fortunes of the kite in Wales and parts of northern and central Europe from where the majority of east coast migrants are thought to originate (Lack 1986). Table 1:

Red Kite records in Suffolk (from Suffolk Birds 1990) 1950s 1960s 1970s 1980s 1 9 15 28

The increase has continued into the 1990s and records thought to involve up to 37 individuals were noted in 1995 and 1996 alone ( S u f f o l k Birds 46, Richard Walden pers. comm.). This is probably partly for the reasons given above and also as a result of the ongoing reintroduction project in England. In recent years, several wing-tagged birds seen in Suffolk are known to have originated from the southern England reintroduced population. The increasing number of records in the first half of the 1990s prompted the following prophetic comment under Red Kite in Suffolk Birds, 6


Fig. 1. Red Kites in Suffolk: Estimated number of individuai each year (based 011 records in Suffolk Birds)

1995: ' With the continuing success of the reintroduction programme in the Home Counties and the new releases in the English Midlands, the optimists amongst us believe that the long-term prospects now look good for this species to re-colonise Suffolk.' At that stage, even the optimists could not have anticipated events over the next couple of years. The return of the kite to Suffolk In 1995 a green-tagged bird, released in southern England in 1993, was present in the same area of south-east Suffolk from at least January 17th to March 20th. It was seen with an untagged bird on February 16th and display was noted, leading to rumours of possible breeding. In the southern England breeding population, one year old kites are known to have bred successfully (Evans et al. in press; Snell, McQuaid & Stevens 1996), something not previously recorded from other populations, but the vast majority of southern England birds breed for the first time at two years of âge. The presence of a two year old bird in seemingly suitable habitat in Suffolk, at the start of the breeding season and in company with a second individuai is therefore indicative of potential breeding. In this case, however, the birds were not seen together after the initial sighting and the green-tagged individuai was subsequently recorded at a communal roost in southern England in October 1995. If the two birds involved were indeed a pair then it seems likely that they either moved away to an alternative breeding site or perhaps attempted to breed but failed at an early stage. Had they bred successfully then there would surely have been further records during the summer. In the spring of 1996, from Aprii 28th onwards, two untagged adult Red Kites were reported regularly within the same well-wooded area, well away from the sightings in 1995 and again leading to rumours of breeding. On May 7th, the local gamekeeper was contacted and it soon became clear from his observations over the previous two week period that the birds were almost certainly breeding. He and his sons had seen 7


two kites circling over the same small area of woodland several times during this period and they had been heard calling on at least one occasion. These observations are strongly suggestive of breeding as non-breeding birds tend to search for food over open countryside rather than woodland, and are rarely heard calling. With the gamekeeper's help, a thorough search of woodland in the area was undertaken and the nest site was eventually located. The nest was about 20m from the ground, in the upper branches of a mature Scot's Pine tree. It was situated well inside a relatively large area of mixed woodland, within a block of trees close to the edge of a large clear-felled area. This allowed the birds a clear flyway into the nest, something typical of kite territories in southern England and Wales where the nest tree is usually close to the edge of a wood. Over the next few weeks a single adult was seen regularly in the area and on occasions was seen carrying food into the wood. This was almost certainly the male bird bringing food to the female, now incubating eggs. On July 6th he nest tree was climbed and two chicks, now about 4 weeks old, lowered to the ground for ringing and tagging. Yellow wingtags (as for southern England 1996 fledged birds) were used, marked with a black '?' on one bird and an '*' on the other. Tagging has already allowed the progress of one of the chicks to be monitored closely. Yellow ? was first recorded in the Midlands in late October 1996 associating with birds released in 1995 and 1996. At the time of writing, in February 1997, it was still present and often joined the communal roost with birds from the reintroduction project. Origins of the breeding pair The absence of wing-tags from either member of the pair by no means proves that the birds did not originate from the reintroduction programme. Although all released birds are fitted with wing-tags, the plastic attachments become brittle with age, probably as a result of exposure to sunlight, and often fall off after three or more years. Wild-fledged chicks from the established reintroduced populations are also fitted with wing-tags before they leave the nest but in recent years it has proved impossible to tag all the young birds in each year. Not all nests are necessarily located each year and of the nests that are found, a small proportion may be too difficult to reach. The reintroduction programme started as long ago as 1989 and untagged adult birds are now not at all uncommon. Chicks from the increasing Welsh population have for several years been colour-ringed rather than fitted with wing-tags. As a result of tag loss from many adult birds and the change to colour-ringing, it is now relatively unusual to see a wing-tagged kite even within Wales. What perhaps makes it unlikely that the Suffolk pair originated f r o m within Britain is the high degree of natal philopatry exhibited by the reintroduced and Welsh kites. (Evans et al. in press; Newton et al. 1994). Birds in their first year regularly wander away from the breeding areas and often travel considerable distances, but, when old enough to breed, the overwhelming tendency is to return to where they themselves were reared (or released). This is by no means unusual for large birds of prey and helps to explain, for example, the scarcity of breeding Buzzards in eastern England, despite the increasing numbers of visiting birds (Walls & Ken ward 1995). In fact, the slow rate of spread of the Welsh kite population and the assessment that natural recolonisation of England and Scotland was unlikely within a reasonable time scale was one of the main reasons for proceeding with the reintroduction programme. It is thought that the partly migratory Red Kite populations in central and northern Europe, probably responsible for the majority of records in eastern counties of England, may exhibit a lower level of natal philopatry and be more likely to breed away from the area in which they were reared. Genetic studies have demonstrated that 8


Fig. 2. Estimated fledging dates of Red Kites in England in 1996

5

10

15

20 25 30 35 Date (days after 20th June)

40

45

an immigrant iemale, almost certainly of German origin, was recruited into the Welsh population sometime in the last 25 years (Davis 1993). Similar genetic work has shown that a breeding bird in the southern England population was an immigrant f r o m elsewhere, the late breeding date suggesting that a continental origin was most likely (Dr Ian E v a n s pers. comm.). A continental origin for the Suffolk pair is also supported by the breeding date, notably later than the average in England (Figure 2) or Wales in 1996 but well within the usuai range of birds breeding in Germany and Sweden. T h e fact that R e d Kites have been increasing in parts of northern and central Europe and have, for example, recolonised Denmark, Belgium, the Czech Republic and Austria during 1970-90 (Tucker & Heath 1994) makes a continental origin seem even m o r e feasible. T h e future for the Red Kite in Suffolk The next f e w years are going to be crucial for the future prospects of the Red Kite in Suffolk. T h e main hope for the early establishment of kites in the county would seem to depend on the 1996 pair continuing to breed successfully over the next f e w years and rearing enough young that survive to breeding âge and also return to the same area to breed. Monitoring work in Wales and southern England has shown that the majority of pairs do return to re-use the same nest, and this is particularly the case if they bred successfully in the previous year. The Suffolk pair has been seen regularly over the winter and, by the time this report is published, they will hopefully have reared another brood of chicks successfully. It is possible that the presence of a breeding pair of kites in the area will encourage migrant kites to stay and breed in the same area and in this way a small colony could become established. There are already signs that this could happen in the Midlands release area where, in early spring 1997, one of the three pairs on territory were untagged birds of unknown origin. If the 1996 Suffolk pair d o not rear any more young and other pairs are not attracted in to join them, then there could be a considÊrable period of time before the next breeding attempt in the county. T h e nearest breeding birds from the reintroduction p r o g r a m m e are over 130km away and as a resuit of the established pattern of natal philopatry could take a great many years to spread as far as Suffolk. 9


Acknowledgements We are particularly grateful to the landowner and local gamekeeper who could not have been more helpful in the initial search for the nest and with subséquent visits. In order to avoid publicising the nest location it is impossible to name them at this stage; in the future, when kites are once again common breeding birds in Suffolk we hope to be able to thank them more directly. Dr James Kirkwood, of the Universities Fédération for Animal Welfare visited the site to take blood samples from the two chicks. Analysis of the D N A by Jon Wetton at Nottingham University Genetics Department has shown that one chick is male and one iemale; further analysis may help to shed light on the possible origins of the parents. Mick McQuaid, Peter Stevens, Nigel Snell, Cliff Waller and David Pearson helped to organise and carry out ringing and wing-tagging of the two chicks. Richard Waiden supplied détails of kite sightings in Suffolk over recent years. References Carter, I., Evans, I. & Crockford, N. (1995). The Red Kite re-introduction project in Britain - progress so far and future plans. British Wildlife 7: 18-25. Davis, P. (1993). The Red Kite in Wales: setting the record straight. British Birds 86: 295-298. Evans, I. M., Cordero, P. J. & Parkin, D. T. (in press). Successful breeding at one year of age by Red Kites Milvus milvus in southern England. Ibis, in press. Evans, I. M., Dennis, R. H., Orr-Ewing, D. C., Kjellén, N., Andersson, P-Ol., Sylvén. M., Senosiain, A. & Carbo, F. C. (1997). The re-establishment of Red Kite Milvus milvus breeding populations in Scotland and England. British Birds 90: 123-138. Holloway, S. (1996). The historical atlas of breeding birds in Britain and Ireland 1875-1900. Poyser, London. Lack, P. (1986). The atlas of wintering birds in Britain and Ireland. Poyser, Calton. Newton, I., Davis, P. E. & Moss, D. (1994). Philopatry and population growth of Red Kites Milvus milvus in Wales. Proc. R. Soc. London B, 257: 317-323. Snell, N. McQuaid, M. & Stevens, P. (1996). Report of the red kite breeding season in southern England. Unpublished. Tucker, G. M. & Heath, M. F. (1994). Birds in Europe: their conservation status. Cambridge: Birdlife International (Birdlife Conservation Series No.3). Walls, S . S . & Kenward, R. E. (1995). Movements of radio-tagged Common Buzzards Buteo buteo in their first year. Ibis 137: 177-182. Editorial note: Suffolk birders will be pleased to know that the same pair bred successfully again in 1997, raising three young. The chicks were marked with red wing tags, the individuáis being identifiable by either ? or * or + on the tag. Results of the DNA tests on the chicks were unfortunately inconclusive as their DNA could not be matched with any known released birds. However, this does not mean that their parents are defìnitely Continental birds, although it is worth noting that the hatching date was again three weeks later than the average for the British population.

10


Sawbill Movements at Landguard Point, Suffolk, 1983-96 Nigel Odin Three species of 'sawbill' have been recorded in Suffolk: Red-breasted Mergansers and Goosanders are uncommon winter visitors and passage migrants whilst Smew is described as a scarce winter visitor (Piotrowski in prep). Landguard Bird Observatory, situated in the south-east corner of Suffolk, has been collecting data on migration since its inception in 1983. The data for sawbills have been analysed for the period 1983 to 1996 to produce the following species' accounts. Red-breasted Merganser (Mergus serrator) The Red-breasted Merganser is the most common of the three species of sawbill to be noted at Landguard. The species has a predominately northern and western distribution in the British Isles with the nearest nesting grounds to Suffolk being in the Peak District (Carter et al. 1993). The species is mostly maritime in winter (Cramp et al. 1977). The numbers noted at Landguard vary greatly from year to year as can be seen in Fig 1. This could be due to a number of reasons, the size of the autumn passage (Fig.l) and the severity of winter weather on the Continent driving birds across the North Sea into Suffolk both suspected as being reasons for this annual variation. Fig. 1. Red-breasted Merganser bird-day totals 1983-96 160 -,

1 Jan-Aug

140 -

ISep-Dec

120 100 -

80 60 40 20 -

0

^ i - ~ i ~~ i

i

i

!

i "

I

i

i

i

i

r

83 84 85 86 87 88 89 90 91 92 93 94 95 96 The seasonal occurrence of Red-breasted Mergansers in 73 five-day periods for the years 1983 to 1996 is shown in Fig.2. This clearly shows a block of records from January to early March which is nearly all associated with severe winter weather conditions from north-western Europe across to the Baltic. The bird-day totals for this period slightly exaggerate the number of individuals involved as Red-breasted Mergansers occasionally feed at the mouth of the River Orwell between the Port of Felixstowe and Landguard Point during harsh weather conditions and individuals can thus be present for protracted periods. The histogram for the rest of the year is mostly made up of birds flying past offshore with birds only rarely seen sitting on the water outside the period January to early March. ll


Fig. 2. Red-breasted Merganser bird-day totals 1983-96 in five day periods

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dee

There is a light spring passage of birds moving both north and south offshore, peaking in Aprii and early May. After the first week of May there are records on two dates in late May, on three dates in June and on four dates in late July. These are thought to involve either stragglers or immature birds in late May and June with the four birds noted in late July probably involving birds moving to moulting grounds. Males leave nesting grounds in early June and moult with immature birds on the coast (Cramp et al. 1977) The only record between July 30th and September 17th is of four flying south on August 15th 1986 which is an odd record as the species is largely flightless at this time of the year. Autumn passage really gets under way in October and November and is largely over by the first week of December. Nearly ali birds are noted flying south during autumn passage. Numbers recorded vary each year (Fig.l); in some years passage is noted on few dates with the bulk of the autumn totals occurring on just one or two days. The largest movements have involved 78 on November 12th 1983, 65 on November 9th 1992 and 47 on October 22nd 1995. In other years smaller numbers occur spread over a greater number of dates. The "big-days" usually coincide with large southerly movements of other wildfowl species and occur when the weather pattern brings onshore winds. It is suspected that these are birds moving from Scandinavia, the Baltic countries and Russia into Western Europe for the winter. This statement is supported in speculation by Chandler (1986) that birds wintering on the east and south coasts of Britain are Scandinavian in origin. Peak passage in the Baltic is in mid- to late October (Cramp et al. 1977). It is slightly later in some years at Landguard suggesting that some birds that may have originated well to the east have stopped en route. Mergansers seen during severe winter weather must have come from the east since the species is maritime in winter and is unlikely to get frozen out from British inshore waters which very rarely ice over. British-bred birds may also be involved in Landguard's records but it has been suggested that most British birds winter on coasts near their natal areas (Chandler 1986). The British population has been increasing and spreading throughout this century (Owen et al. 1986) despite suffering from both illegal persecution and licensed killing in the name of fisheries protection (Carter 1993). If the spread continues then the likelihood of British-bred birds occurring regularly at Landguard increases. 12


Goosander ( M e r g u s merganser) Like its near relative the Red-breasted Merganser, Goosanders nest mostly in upland areas of northern and western Britain. The species was first recorded nesting in Britain a little over one hundred years ago and is still spreading southwards despite persÊcution by people interested in exploiting fisheries. The nearest nesting grounds to Landguard are in Derbyshire (Carter 1993). Unlike Red-breasted Mergansers, Goosanders occur largely on fresh water in winter. Over much of its world range the Goosander is either resident, or moves rather short distances between breeding and wintering areas (Owen et al. 1986) At Landguard numbers recorded annually vary sharply (Fig 3.) with the species considered a scarcity by regulär Landguard observers. None was seen in two of the years under review (1984 & 1990). The maximum recorded on any one day is 28 south and five east on January 2nd 1996. The bulk of records are of birds flying south or moving west in off the sea and inland. The numbers seen annually are possibly related to conditions in eastern Europe and Russia and it will be interesting to see if numbers increase should the species continue to expand its breeding range closer to Suffolk. Fig. 3. Goosander bird-day totals 1983-96

83

84

85

86

87

88

89

90

91

92

93

94

95

96

The seasonal pattern of occurrences in 73 five-day periods (Fig. 4.) for the years 1983 to 1996 shows two distinct movements. A January influx which correlates with, and ties in with. known influxes into southern England at this time of the year (Owen et al. 1986). January records at Landguard do not always coincide with severe winter conditions elsewhere and can occur in any weather. The February records are always associated with harsh weather conditions which cause the species to relocate as feeding grounds freeze over. A couple of sightings of birds on spring passage have been noted in March. The species is unrecorded at Landguard from March lOth to October 14th except for two on September 18th 1983 (although the reliability of this September record has been questioned). Autumn passage runs from mid-October to early December (Fig.4.), producing two peaks on the histogram in the middle of October and in the middle of November, the reasons for which are unclear. The passage late in the autumn is perhaps due to the fact that the species remains near to the breeding grounds for as 13


Fig. 4. Goosander bird-day totals 1983-96 in five day periods 40 ! 35 30 25 20 15 â&#x20AC;˘ l Jan

i Feb

Mar

Apr

May

Jun

Jul

Aug

. Sep

H Oct

. Nov

Dec

long as the waters stay unfrozen. A mass departure of such areas takes place on the advent of freezing, a major movement through the Baltic occurring in October and early November (Cramp et al. 1977). Birds breeding in central and northern Scandinavia, Finland, the Baltic countries and Russia east to the Pechora migrate west to the Baltic and Britain (Cramp et al. 1977). As British breeders are almost entirely resident with most moving only a short distance from breeding areas (Cramp et al. 1977, Owen et al. 1986) it is fairly safe to assume that Goosanders seen at Landguard in the autumn are long-distance migrants from eastern Europe and Russia. January movers past Landguard are also probably from the same areas as waters are progressively frozen over as winter progresses. Birds seen at Landguard associated with severely cold winter weather conditions could have originated anywhere as the species seeks refuge from fresh waters icing over. The numbers seen annually (Fig.3.) are possibly related to conditions to the east of Landguard and it will be interesting to see if the numbers recorded increase if the species continues to spread its breeding range nearer to Suffolk. Smew (Mergellus albellus) Smew are only very rarely seen at Landguard. Very few winter in Britain except during the onset of severe winter weather conditions on the Continent (Owen et al. 1986). The species has been noted twice on autumn passage with singles flying south on November 16th 1989 and October 27th 1992 and Smew are only very rarely recorded on autumn passage in the whole of Britain. More expected records occur during severe winter weather, with singles flying south on January 18th and 22nd 1985 and in February 1991, records of 15 south on 10th, eight south on 11th and three up river on 12th. These constitute all the Landguard records at the time of writing. The nearest breeding grounds are in northern Scandinavia and Russia. The European breeding population is under threat (officially designated "vulnerable") and is of conservation concern largely as a result of prĂŠdation by the introduced American Mink Mustela vison (Vinogradov 1994). With the nearest winter concentrations being in the Netherlands (Cramp et al. 1977), it is thought that frozen Dutch wintering grounds are the likely origin of birds moving into Suffolk. 14


Acknowledgements: Thanks to Mike Marsh for commenting on the above and to all those members of Landguard Bird Observatory who take the time to put their sightings on paper. References: Carter, (1993) in Gibbons, D. W. et al (Eds.) The New Atlas of Breeding Birds in Britain and Ireland: 1988-1991 pp90-93. T & AD Poyser. Chandler, R. J. (1986) in Lack, P. (Ed.) The Atlas of Wintering Birds in Britain and Ireland, pp 126-127. T. & A D Poyser. Cramp, S. & Simmons, K. E. L. (Eds) (1977) The Birds of the Western Palearctic Vol.1. OUP. Owen, Mâ&#x20AC;&#x17E; Atkinson-Willes, G. L. & Salmon, D. G. (1986). Wildfowl in Great Britain. pp 451-460. CUP. Piotrowski, S. H. (in prep.) The New Birds of Suffolk. Vinogradov (1994) in Tucker, G. M. & Heath, M. F. Birds in Europe : Their Conservation Status. Cambridge, U.K.; Birdlife International (Birdlife conservation series No.3.). Nigel Odin, c/o Landguard Bird Observatory,

15

View Point Road, Felixstowe, Suffolk IP 11 8TW


Seabird Movements and Abundance off Covehithe, Suffolk, 1994-96 I. Fulmar, G a n n e t , Kittiwake, Guillemot and Razorbill P. J. Dare Introduction Although sea-watching has become a popular pastime at various sites, especially in autumn, few studies of seabird movements have been published even for the most intensively watched locations. Among the most detailed analyses, some confined to particular species, are those for Anglesey (Dare 1996), Bardsey (Rowley & Jones 1980), north Kent (Davenport 1969, 1987, 1991a), the English east coast (Wallace & Bourne 1981), north-east Scotland (Elkins & Williams 1970) and North Uist (Davenport 1991b). More general accounts of seabird movements, and especially of unusual influxes or passages, appear sporadically in some county reports and avifaunas, and in British Birds (e.g. Fox & Aspinall 1987). In Suffolk investigations began in 1987 with the regular recording of seabirds observed from the cliffs at Covehithe, between Lowestoft and Southwold, where several notable passages were documented over the next three years (Cawston & Ling 1988, 1989). Those efforts, like others elsewhere, were concentrated on the autumn migration although attention was directed later also at spring movements. It was discovered that large and varied passages could occur off this coast, particularly in association with strong NW-NE winds, and that the status of many of the more pelagic species had been underestimated, in particular that of shearwaters, Gannets and skuas. Despite these pioneering efforts, however, the year-round abundance of many seabirds in Suffolk has remained poorly described. This paper presents some of the results from a study made during 1994-96 to try and rectify some of the deficiencies in our knowledge of seabirds off the north Suffolk coast. It is based on systematic recording throughout each year at Covehithe. The aims were to measure seasonal patterns of occurrence and changes in the composition of the seabird fauna, and attempt to relate the principal movements to weather and other factors. The results are compared with anecdotal records published in the annual bird reports of Suffolk, Norfolk, Essex and Kent. Five of the commonest species will be dealt with here - Fulmar, Gannet, Kittiwake, Guillemot and Razorbill. These form a group characterised by having large breeding populations along the North Sea coast (north of Flamborough Head) and by overwintering in the North Sea in large numbers (Tasker et al. 1987, Lloyd et al. 1991). The movements of terns, skuas and the less common species will be dealt with in later papers. Certain inshore species - Shag, Cormorant and the commoner Larus gulls - were not studied as, excepting the first, many were daily commuters from nearby roosts or breeding colonies. Methods This study is based on early morning observations as this is the time when most passing seabirds are likely to be visible from the coast (Dare 1996, Cawston & Ling 1988). From the 30 ft high cliff-tops at Covehithe a total of 625 such watches (1,565 hours) was spread through every month of the three-year period, thus covering 62% of available mornings (Fig.l). Effort was highest (75% of dates) over the spring and autumn migration seasons and lowest (28%) in June when most seabirds were away at their breeding colonies. An additional 69 afternoon watches (104 hours) were undertaken but these were normally much less productive and are not analysed here. Watches were started usually near sunrise and lasted from 1-8 hours, typically 1.5-3 hours, depending on weather conditions and magnitude of bird movements. 16


Fig. 1. Seawatch Effort, 1994-96 hours 300

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Ali sightings were made using a Kowa T S N 2 telescope (x30WA lens) supplemented at times by 10x50 binoculare f r o m the shelter of local features or a fisherman's umbrella. T h e coast-line here runs N N E - S S W and faces eastwards so that early morning sun giare, sometimes exacerbated by haze, was often problematical. A polarising filter helped significantly to mitigate such adverse viewing conditions. Seabird counts, group sizes and flight directions were logged together with ranges, behaviour and times of any unusual events. Gannets were aged (as juveniles, older immatures or adults) by the method of Nelson (1978). Little Terns nesting close by, and foraging to and fro during M a y to July, were not counted. Weather variables were recorded - wind direction and force (Beaufort scale), visibility, and light conditions as well as sea state. The circa-daily watches spanned a very wide range of weather conditions and thus avoided the seawatcher's traditional bias in favour of strong onshore winds. The results are presented as monthly mean values. For each species, seasonal changes in status at Covehithe during 1994-96 will be described in terms of: (a) the total numbers of birds seen each month and year; (b) the average numbers seen per hour each month, with directions of flight; (c) the monthly frequency of occurrence (as percentage of days on which observed). The m a j o r individuai day movements are then compared with those recorded during 1983-93 in Suffolk Bird Reports (SBRs) and, where possible, related to weather and other factors. Finally, the Suffolk data are placed in a rĂŠgional context by using information in the Norfolk, Essex and Kent Bird Reports (NBRs, EBRs, KBRs) covering the same period. Results 1. Weather during 1994-96 Sea watches Weather conditions critically affect the numbers of 'true' seabirds that approach within viewing range of a coastal observer. The years 1994-96 at Covehithe were characterised by a paucity at peak migration times of the strong to gale (force 6-8) N E to N W winds which usually drive many seabirds close to the East Anglian coasts (Cawston & Ling 1988, 1989; Norfolk and Essex bird reports). Although at Covehithe winds f r o m N E to N W occurred on average on about 30% of days in spring and autumn (Fig.2a) winds f r o m any direction seldom exceeded force 5-6 (Fig.2b). Indeed, gales or near-gales from any direction were unusual, except in January17


Fig. 2a. Wind Directions, 1994-96 % days

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Fig. 2b. Wind Speeds (Beaufort), 1994-96 % days

month •<K>

£3«

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Fig. 2c. Visibility, 1994-96 % days

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Hpcor


February (Fig.2b). Direct onshore winds from between E and SE were rather uncommon and seldom of any strength, whereas for about 40% of watches the winds either blew offshore (from SW to W) or else conditions were cairn. Early morning visibility (Fig.2c) was generally good or very good out to 2-3 miles. It was moderate (<1 mile) or poor (<0.5 mile) most often in spring due to sun giare and attendant haze during NE-SE winds. 2. General Features of Seabird Movements Some 53,000 seabirds from 18 to 20 species were recorded (Table 1 ). The greatest diversity (15 species) was found in August and September, the lowest (six species) in March. The largest numbers of birds were seen in August and January, the least in June and December (Fig.3a). However, when observation times are taken into account (Fig.3b), birds were relatively most numerous in January, 'fairly numerous' in February and August, and least plentiful in December. As seabird migration comprises a sĂŠriĂŠs of episodic, weather-related events, as seen from the shore, these average passage rates could be greatly exceeded by some species on mornings of particularly strong movements. The highest rate, 633 birds per hour (mainly Kittiwakes), was for a watch in January; otherwise few exceeded 100 per hour in other months. Fig. 3a. Seabird Totals, 1994-96

Fig. 3b. Seabird Passage Rates, 1994-96

19


Fig. 3c. Seabird Diversity, 1994-96 no.species 15

12 9 6

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month Fig. 4a. Seabirds: Covehithe, winter (

0-3%) F limar

(

0-0%) Shearwaters

(

2*2%) Gannet

( 79-0%) KittĂŹwake ( 01%) Little Gull (

00%) Tems

(

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( 18-1%) Auks (large) (

0-0%) Little Auk

(

00%) Puffin

= 14,058 Fig. 4b. Seabirds: Covehithe, spring ( 15-1%) Filmar (

00%) Shearwaters

( 56-5%) Gannet ( 12-6%) Kittiwake (

00%) Little GĂŹ*

( 11-7%) Tems (

0-5%) Skuas

(

3*6%) Auks Oarge)

(

00%) Little Auk

(

0-0%) Puffin

= 13,210

On a daily time-scale, seabird movements typically were heaviest within the first 1-3 hours after sunrise, irrespective of weather conditions or time of year. Thereafter, a few individuals, mainly of the commoner species, sometimes continued moving well into the afternoon. As expected from earlier reports (Cawston & Ling 1988, 1989). the largest numbers of birds and species tended to appear on mornings with, or 20


Fig. 4c. Seabirds: Covehithe, summer (

7-9%) Fulmar

(

0*4%) Shearwaters

( 34-0%) Gannet ( 12*9%)Kittiwake ( 4*2%) Little Gull

I ( 37-6%) Tems 1 *0%) Skuas |(

2*0%) Auks (large)

( 0*0%) Utile Auk j ( 0-1%) Puttin

n = 2,672

Fig. 4d. Seabirds: Covehithe, autumn (

4-8%) Fulmar

( 0*1%) Shearwaters ( 30*5%) Gannet ( 17*6%)Krttiwake (

3*7%) Little GUI

( 27-9%) Tems (

3*1%) Skuas

(

7*7%) Auks (large)

(

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(

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n = 22,797 immediately after a day of, strong winds blowing from between NW and NE. With a more or less straight coast-line and a scarcity of strong onshore winds during main migration periods, most seabirds flew past Covehithe at medium or long ranges (0.5-1 mile or more). However, with fresh or strong onshore (NE-SE) winds more birds could be seen within 0.5 miles of the cliffs. Two species, Kittiwake and Gannet, made up 62% of ail seabirds recorded (Table 1 ). At the other extreme, skuas ( 1.6%) were scarcer than either Little Auks (2.0%) or Little Gulls (1.9%) while shearwaters were rare (0.07%). No small petrels or Sabine's Gulls were found. In winter (December-February) Kittiwakes (79%) and large auks (18%) dominated the population (Fig.4a). In spring (March-May) Gannets (56%) appeared in large numbers, Fulmars (15%) increased and sea-terns (12%) arrived as the winter birds departed (Fig.4b). During summer (June-July) Gannets (34%) and terns (38%) were most numerous (Fig.4c). Through autumn (August-November) these same species stili comprised more than 58% of the seabird assemblage (Fig.4d) which was then at its most diverse as shearwaters, Little Gulls, skuas and Little Auks reached annual (if small) peaks during their autumn migrations. 3. Species Accounts (i) Fulmar Fulmarus glacialis The 3,343 Fulmars observed at Covehithe during 1994-96 displayed prominent spring (April-May) and autumn (August) passage periods which contrasted 21


with a scarcity f r o m O c t o b e r to January or February, and a virtual absence in N o v e m b e r (Figs. 5a-c). In June and July the small numbers seen regularly included several individuals behaving as if prospecting the earthy cliffs for nest sites. Their to and fro fly-pasts were not counted. Most other Fulmars at this season were perhaps c o m m u t i n g to and f r o m the small breeding colony at Bawdsey, 30 miles to the south, w h e r e up to 24 birds were reported to be present f r o m January to July in 1994. Fulmars flew predominantly (90%) north throughout the year (Fig. 5b). During the spring movements, which peaked between mid-April and late May, 9 4 % flew north. T h e strongest m o v e m e n t s then were during N - N E winds and included a notable 4 1 2 north in 8.5 hours on April 16th 1996, following several days of fresh/strong N - N E winds, and 123 north in 3.25 hours on May 20th 1994. Most birds moved within 2 hours of sunrise, 213 in the first hour or so on the former date. Blue-phase Fulmars were observed on May 5th 1994 when a group of three flew south close inshore, constituting only the third county record. This northern form occurs almost annually, and in any month, off the north Norfolk coast and at times in large numbers off Flamborough Head. Fig. 5a. Fulmar, 1994-96 number

month ^1994

1995

1996

Fig. 5b. Fulmar, 1994-96

22


The main autumn passage was confined to August when birds passed daily and 87% headed north. However, movements were small (<60 birds per morning). Late August was the peak period and most Fulmars occurred during and following days of light or moderate W N W - N N W winds. They then became uncommon by late September, when adults are moulting at sea (Wallace & Bourne 1981), and were almost rare (three sightings) from mid-October until early December; only three birds were seen during these 1.5 months of the year. The SBR records for 1983-93 also show that spring passage occurs from mid-Aprii until late May though individuai movements were usually small. The largest was of 82 Fulmars north in 2.5 hours on the comparatively late date of June lst in 1991 during strong NE winds. The large spring movements of 1994 were noted elsewhere down the Suffolk coast: 185 north off Minsmere on Aprii 15th and 233 north at Southwold on May 2lst. In autumn, during the above years, seven movements of Fig. 5c. Fulmar, 1994-96

%days

month 50-90 Fulmars were documented between late July and mid-September off Covehithe and Southwold. In four of these most or ali birds were flying south, twice with fresh or strong SE winds and twice with moderate-strong WNW-NNW winds. During a strong-gale ENE blow on September lOth 1989, an exceptional passage of 403 Fulmars heading north was seen from Covehithe. In contrast, the largest winter numbers yet recorded were 50 north on December 2nd 1987 at Covehithe, and 21 north on February 23rd 1986 off Minsmere; both followed fresh-strong northeasterlies. The biggest influxes of Fulmars to Suffolk waters therefore occur generally during or immediately after NW-NE winds exceeding moderate-fresh in strength (Beaufort force 4-5). Southerly movements are unusual but can occur in autumn with fresh (or stronger) SE winds. Comparatively few Fulmars reach Suffolk compared with the magnitude of stormdriven movements that can be seen along the north Norfolk coast in autumn. There, thousands may appear during northerly gales. Between 1983-94, for example, more than 1,000 Fulmars (maximum 7,600) in a day were counted on ftve occasions, ali in September. Even fewer Fulmars penetrate south of Suffolk into the outer and inner Thames areas (Fig. 9) off Essex and north Kent. During the period of this review the highest Essex count was of only 14 Fulmars. However, on the Kent side off Sheppey they are more common and up to 65 have occurred in Aprii. 23


Fig. 6a. Gannet, 1994-96 number

ÂŁ3 1 9 9 6

|1994

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Fig. 6b. Gannet, 1994-96 no./hr

30

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(ii) G a n n e t Morus bassanus This was the second most numerous seabird off Covehithe during 1994-96, with a total of 16,020 birds being recorded, of which 15,636 were seen during morning watches and 384 in the afternoons. In 1996 alone, 7,076 Gannets (6,940 in mornings) were counted. They occurred almost daily f r o m March into N o v e m b e r (Figs. 6a-c) but were least frequent in December. Like the Fulmar. they displayed prominent peaks in both spring ( M a r c h - M a y ) and autumn (August-October) separated by reduced numbers in m i d - s u m m e r (June-July) and relative scarcity in winter ( D e c e m b e r to mid-January). M a n y Gannets m o v e out of the North Sea in winter and return f r o m February-March onwards (Lloyd et al. 1991). The spring m o v e m e n t s overall c o m prised slightly more birds (49% of total) than did those of autumn (43%). T h e âge structure of Gannet flocks changed markedly through the year (Fig. 6b). In spring, on average, 9 6 % of Gannets seen were adults until the end of April, as were 7 9 % up to late May in which month significant numbers of immatures in first- to fourth-year plumages began to appear. The f e w e r birds passing in June and July were predominantly (83%) immatures, any adults then presumably being non-breeders. T h e 24


nearest colony, at Bempton, is 150 miles to the north whereas most Gannets forage within 90 miles of their colonies and many within only 25 miles (Lloyd et al. 1991 ). Autumn birds were also mainly immatures (72%) with few adults (16%) and a sprinkling of juveniles (12%). The last group first arri ved in late August or early September and had passed through by mid-November. Thus, after breeding, few adult Gannets dispersed south after breeding through Suffolk waters compared with the numbers of adults seen heading north in spring. North-bound flights predominated throughout the year off Covehithe; 97.5% of Gannets observed flew north during January-May, 85% did so in June-July, and 89% in autumn. No directed southerly passage was seen, merely sporadic movements by individuai birds and very small groups. Spring Gannets typically headed north in compact flocks or straggling lines of up to 35 birds, often at 50-100 ft élévation, depending on the conditions. In fresh or strong onshore E or NE winds, and thick haze, the flocks often passed only 200-300 yards offshore. On some clear mornings with light winds, however, high-flying flocks could be seen 3-4 miles out, Coming up from the south or south-east. Usually, few Gannets were seen in the first hour of a watch, most passing with a marked peak between 1-3 hours after sunrise, consistent with dawn origins 30-90 miles to the south in the outer Thames area or the Dover Strait. In summer and early autumn, similar flocking was observed at Covehithe. Surprisingly, perhaps, Gannets seldom paused to fish though up to four individuáis might make exploratory dives on some days. The habit of Gannets moving in discrete flocks off this coast (which is not seen off west coast seawatch points in autumn (Dare, pers. obs.)) may result from their behaviour in autumn off Sheilness, north Kent. There, during northerly winds, Gannets often collect overnight into small groups before moving back out to sea, at least some of them probably returning north past the Suffolk coast (D.Davenport, pers. comm.). During 1994-96 at Covehithe 40 large movements were recorded, each of more than 100 Gannets, passing at an average of 45 birds per hour. Of these, 24 were in spring (between March 7th and May l l t h ) and 15 in autumn (between August 9th and September 16th) plus a very late movement on October 2Ist. The three largest spring movements were:- (i) 560N in 9 hours with wind NE force 4-5 on April 16th 1994; (ii) 4 4 I N in 3.25 hours with wind E-NE force 4-5 on April 5th 1996; (iii) 426N in 5.75 hours with wind W force 3, but after a strong northerly, on March 30th 1995. Fig. 6c. Gannet, 1994-96

% days 1X 80 60 40 20 J

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In autumn, by contrast, the biggest m o v e m e n t was of 205 birds ( 2 0 I N , 4S) in 5.5 hours on August 9th 1995 after a N N E wind force 4-5. Such big passages could extend into the early afternoons when otherwise only occasionai Gannets might be expected. Although Gannets passed Covehithe under all wind conditions, including calms, it was the direction and strength of wind on the previous day/night which generally determined Gannet numbers, whereas the wind on a given morning mainly influenced their distance f r o m shore. Thus, 80% of the above large m o v e m e n t s followed N W - N E winds, 8% westerlies, 10% S - S W winds and 2 % were after cairn days. T h e origins of the large spring m o v e m e n t s are problematic. Those following S - S W winds and calms happened only in spring thereby suggesting that birds were Coming north through the Dover Strait. T h e 12 large m o v e m e n t s in N E winds could have derived either f r o m similar true passage migrants or f r o m the re-orientation of birds that were already in the North Sea and had drifted far south overnight into the outer and inner T h a m e s areas. In s u m m e r and autumn, ali north-bound m o v e m e n t s after N W - N E winds could only resuit f r o m southerly displacements and subsequent returns to feeding grounds in the southern and centrai North Sea. Fig. 6d. G a n n e t s off Suffolk, 1983-93 (data f r o m Suffolk Bird Reports) number

C o m p a r i n g the 1994-96 data with the earlier Suffolk records strongly implies that Gannets have been much under-recorded, particularly in the spring. Of the total of 13,319 birds enumerated during 1983-93, 7 7 % were in autumn and only 12% in spring (Fig. 6d ), an identical ratio to that noted in Essex Bird Reports, and doubtless reflecting observer bias in f a v o u r of autumn sea-watching and more especially during September and October. M o s t of the S B R spring records, in fact, stem f r o m the 1987-89 Covehithe studies of Cawston and Ling (1989). They observed two large northerly m o v e m e n t s of 324 and 273 Gannets during strong onshore winds in early March 1988 (Table 2). In autumn, observer bias may explain the much higher proportion (65%) of large m o v e m e n t s recorded in September-October than was the case (38%) during 1994-96. Indeed, the two highest autumn counts listed in the SBRs (and Table 2) were both in early O c t o b e r : - 2 4 2 N during and after strong E - S E winds, and an exceptional 526 (446N, 80S) off Covehithe in fresh-strong N - N W winds on October 8th 1989. Three of the 17 autumn m o v e m e n t s were associated with freshstrong E - S E winds, the rest with W N W - N E winds. T h e only two southerly m o v e ments observed both followed N W blows and were rather s m a l l : - 88S (and 11N) on August 2 I s t and 88S (but 5 0 N ) on September 5th. Thus, the 11-year SBR record supports the interprĂŠtation of the 1994-96 observations as outlined above. 26


In north Norfolk, much larger Gannet movements - sometimes of 1,000 to 2,300 birds in a day - can be generated by strong or gale force onshore NW-NE winds between late August and early October, with around 90% of birds flying east along the coast (NBRs, pers. obs.). Undoubtedly, some of these Gannets reach Suffolk waters. Indeed, many are then driven far south into the Thames as evidenced by counts of 379 in Essex, at Canvey, and up to 1,333 off Foreness in north Kent (EBRs & KBRs 1983-95). Finally, it is probable that Gannet numbers off Suffolk have increased markedly over the past 25 years due to the development of the Bempton breeding colony just north of Flamborough Head. There, numbers have risen dramatically from 18 pairs in 1970 to 1,036 pairs rearing 720 juveniles in 1990, and to 1,820 pairs in 1996 (Lloyd etal. 1991, RSPB 1996). (iii) Kittiwake Rissa tridactyla This was the most numerous seabird, with some 17,000 being recorded during 1994-96 (Fig. 7a), although Kittiwakes, in fact, were seen on fewer days than were Gannets (Figs. 6c, 7c). Annual abundance varied markedly from more than 10,000 birds in 1995 to only 2,600 in 1996, and highest numbers appeared annually in January and February as well as (once) in October (Fig. 7a). In other months surprisingly few Kittiwakes were noted, being almost scarce in March, and again from July through September. Most (>90%) birds seen in the breeding season were adults, presumably from the small Lowestoft colony (222 pairs in 1994) rather than from the distant and much larger colonies at Flamborough or in the Dover Strait. Fig. 7a. Kittiwake, 1994-96

Ten of the 12 highest counts (>500 birds) were in winter between mid-January and mid-February, the largest involving at least 1,900 flying north into a fresh-strong northerly wind in three hours on January 26th 1995. In seven other winter movements all the Kittiwakes flew south into moderate-strong SW winds, while in two others 80-83% did so. On four mornings large flocks fed intensively in the wakes of large ships which they followed south. Most likely their food was sprat shoals brought to the surface by propeller turbulence (D. R. Eaton, pers. comm., and see below). In contrast, the only two large autumn movements were both northerly and occurred in light-moderate N-NNE breezes following stronger W or NNW winds the previous d a y : - (i) 1,690 (>90% juveniles) north in 5.5 hours on October 21st 1995, (ii) 665 north in seven hours on November 4th 1995. 27


During 1983-93 much bigger movements were recorded in Suffolk (SBRs) but more often in autumn than in winter (Table 2), perhaps reflecting observer bias towards autumn sea-watching. An exceptional movement of ca.6,000 Kittiwakes in only two hours headed into a SW gale off South wold on January 10th 1993 and 600 were feeding off Minsmere on February 21st 1993. Three other winter movements were much smaller (500-1,500 birds); two occurred in fresh-strong south-westerlies and one during strong-gale force N-NNW winds. That some movements are linked with feeding opportunities is confirmed by the massive influx of an estimated 20,000 Kittiwakes between Sizewell and Thorpeness on January 7th 1996. These were feeding, with thousands of other gulls, on sprat shoals very close to the beach (D. Fairhurst, pers.comm., S.O.G. Bulletin 108). At Covehithe, in contrast, only 1,040 Kittiwakes were seen throughout January 1996 (Fig. 7a). Fig. 7b. Kittiwake, 1994-96

Jnorth

f x ] south

Fig. 7c. Kittiwake, 1994-96

% days KXH

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In autumn (late August - early November) the SBRs record ten large northerly movements of Kittiwakes along the north Suffolk coast, of which seven were in freshgale force NNW-NE winds, two in fresh-strong E-SE winds and one with a SW gale. The two heaviest passages involved 3,000-4,000 birds off Lowestoft in a strong 28


northerly on November 2nd 1986 and 2,500 off Covehithe in a SW gale on October 22nd 1984. Thus, most large Kittiwake movements appear to be triggered by two contrasting sets of weather conditions according to season. Either, as in autumn, they occur after strong NW-NE blows (when most birds fly north after being blown southwards overnight into the greater Thames area, some as far as the Essex and Kent coasts - see below) or, as in mid-winter, during strong SW winds (when most head south into the Thames). The latter behaviour could represent birds returning to feeding grounds in the outer and inner Thames areas (Fig. 9), having been drifted offshore in the night. Many Kittiwakes appear off the south Essex coast and off north Kent regularly between December and February, often in association with sprat shoals (EBRs. KBRs); up to 1,500 gathered off Southend in February 1994 while winter movements of 8,000 to 16,000 Kittiwakes occurred off Foreness in the 1980s (Davenport 1991a). Autumn influxes occur more sporadically along these Thames coasts during N-NW gales in October-November when up to 2,500 may pass Sheppey and several hundreds may even penetrate the River Thames at Canvey Island and Allhallows. Along the north Norfolk coast very large Kittiwake movements (2,000-5,000 birds) are not unusual when N and NE gales blow between September and early March, though more especially during October-November (NBRs). Several massive displacments, of 10,000-20,000 birds, have been witnessed in recent years. Storm-driven Kittiwakes fly predominantly (>90%) east along that coast and many therefore should become vulnérable to southerly displacement into Suffolk waters and the Thames Estuary. (iv) Guillemot Uria aa/ge/Razorbill Alca torda These two large auks were seldom separable specifically due to the ranges at which they passed Covehithe. However, the great majority would have been Guillemots; these outnumber Razorbills in the North Sea by 9.3:1 (Tasker et al., 1987). Guillemots also comprised 90% of live large auks (n=2,828) identified in Suffolk in recent years (SBRs). At Covehithe during 1994-96 only one Razorbill was observed among the 141 nearest auks, i.e. 99.3% were Guillemots. Large auks were far less plentiful than either Gannets or Kittiwakes. They appeared most frequently between October and March (Fig.8c ) but were numerous only in November and January (Figs.8a-b). Each year they were scarce in Aprii and from July Fig. 8a. Guillemot/Razorbill, 1994-96 number 1800 1500 —i 1200 900 600 300

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month |1994

Ê31995

D1986 29


to September, and were absent during August (when moulting auks are flightless in the central and northern North Sea). A slight northerly spring passage was evident in May-June each year involving at least a few Guillemots in the dark breeding plumage of the northern race aalge in May (total of ten individuals). Like Gannets, nearly ail (>95%) auks flew north throughout the year, southerly movements occurring only in January and February. (Fig.8b ). Most auks passed Covehithe in the first few hours of daylight although two movements did not start until late morning. Very few birds moved in the afternoons. During 1994-96 there were nine movements (eight northerly, one southerly) of 100 or more auks, five being in January, three in November and one in December. Ail occurred in W or NW winds, usually moderate to strong; five followed days with light to moderate W or NW winds, one each after SW, N and SSE moderate to strong winds, and one after a cairn day. The two biggest movements were: (i) 588N in a moderate north-westerly on November 13th 1996, and (ii) 400N in a strong WNW wind on January 28th 1994. The only southerly movement observed was of 160 auks on January 23rd 1994 in a fresh westerly. The 1983-93 SBRs note 11 movements of more than 200 auks, apparently ail northerly, off the north Suffolk coast (Table 2), five of which were stated to comprise only Guillemots. They took place in January (2), March (1), October (5), November (1) and December (2). Seven of them occurred during or following fresh-strong N-NW winds, one with a near-gale force westerly and three were associated with strong-gale NE-SE blows. The two heaviest auk passages were: (i) 724N (county record) in only two hours of E-NE winds at Southwold on December 16th 1990, and (ii) 356N in a fresh northerly off Corton on October 9th 1989. By contrast, the highest count of Razorbills in the 11 years was of 35 birds off Minsmere. In Suffolk, therefore, large movements of these auks nearly always head north and they generally coincide with fairly strong winds from either the N-NW or E-NE sectors. On the north Norfolk coast large eastwards movements are often observed when strong or gale force onshore winds blow from between NW and NE during the autumn and winter. Typically these may involve maxima of 1,000-2,000 auks, but several massive passages have occurred since 1982. In October 1992 a total of 12,200 auks flew east in six days, including 6,100 on one day, while on February 20th 1994 an estimated 10,000-20,000 passed east (NBRs). Although at least 2,000 of the latter birds continued south past Waxham no large movements were reported off the Suffolk Fig. 8b. Guillemot/Razorbill, 1994-96 no./hr 18 15

12 9

6 3 J

F

M

A

M

J

J

A

S

O

N

D

month Jrxxth

[^saih 30


Fig. 8c. Guillemot/Razorbill, 1994-96

% days 100-1

80

40

Hi.llJ

F

M

A

M

J

J

A

.lll S

O

N

D

month coast that day. Similar weather conditions during May to July can produce smaller influxes (up to 1,000 auks) to Norfolk, these presumably being foraging birds from the breeding colonies in Yorkshire. Despite the large scale of auk movements in north Norfolk rather few birds are driven into Suffolk waters and even fewer reach the Essex coast, where the highest count during 1983-93 was of only 112 birds. In north-east Kent, by contrast, many auks fly east past Foreness in winter after having been deflected briefly into the outermost limits of the Thames rĂŠgion. At Foreness, peak easterly movements averaged 1,410 auks during the 12 winters between 1979/80 and 1990/91, with the two largest movements involving 2,579 and 4,623 birds (Davenport 1991a). Discussion The 1994-96, and earlier, Covehithe observations now enable us to assess the scale and diversity of seabird movements off Suffolk throughout the year, to set them in both a regional context and a North Sea perspective and to understand something about patterns of occurrence in relation to life cycles and meteorological influences. The numbers of Fulmars, Gannets, Kittiwakes and large auks recorded off Suffolk are low compared with those reported at other east coast sites further north, amounting typically to only a few hundred birds even during locally notable movements. Only Kittiwakes may occur in the low thousands, during their occasionai winter influxes to forage in the wider Thames area. Although these species are all more numerous off our coast than further south off Essex they are generally far more abundant - often by one or two Orders of magnitude - along the north coast of Norfolk. Such regional diffĂŠrences reflect the location, shape and orientation of the East Anglian coastline with respect to the distribution of seabirds feeding at sea and to the incidence of those particular meteorological conditions (streng NW-NE winds) that generate large southerly displacements of seabirds and lead to impressive coasting movements around the southern North Sea ( Wallace & Bourne 1981, Camphuysen & van Dijk 1983), particularly during the autumn migration period. Each of the five species considered here has large breeding populations on the coasts of north-east Britain. They also overwinter abundantly (Table 3) in the central and northern North Sea, to the north of a hydrographie boundary that extends from east of Flamborough Head across to near the Friesian Islands (Fig. 9). (most shearwaters, skuas and Little Auks are also to be found here in season (Tasker et al. 1987)). This boundary separates the deeper, more productive and clearer waters of the 31


Fig. 9. Map of the North Sea showing the subdivisions, approximate location of the hydrographie boundary (dotted line), and of seawatch sites mentioned in the text. C - Covehithe, CV - Canvey, CGN - Cap Gris Nez, D - Dungeness, F - Foreness, FH - Flamborough Head, IT - Inner Thames, OT - Outer Thames, S - Sheringham, SY - Sheppey. Atlantic inflow (coming around the north of Scotland) from the shallow, mixed and turbid water to the south. The latter rĂŠgion, or Southern Bight, separates the English east coast, south of the Humber, from the Dutch and Belgian coasts. Relatively few seabirds penetrate into the Southern Bight during most of the year but even so considĂŠrable populations (Table 3) may be present not far off the East Anglian coasts though generally well dispersed in spring and summer (Tasker et al. 1987, Camphuysen et al. 1995). They become more concentrated in autumn and winter around trawlers (Fulmars, Gannets and Kittiwakes) and at herring shoals (Gannets, Kittiwakes and auks) off the Dutch/Belgian coasts (Tasker et al. 1987, Camphuysen et al. 32


1995). Exceptional numbers of Fulmars may be driven south by severe northerly storms in winter, as in February 1993 (Table 3), although no corresponding coastal influxes were reported in East Anglia at that time. The eminence of the north Norfolk sea-watching sites can be attributed to two main factors: (a) proximity (70-100 miles) to the major source population of seabirds feeding in the central and western North Sea, and (b) the east-west orientation of the coast which thus protrudes nearly at a right angle across the flight paths of birds moving south, whether migrating normally or under the influence of strong northerly winds. Conversely, in such wind conditions, the Suffolk coast then experiences either offshore winds or, if a north-easterly is blowing, only an obliquely onshore wind. Consequently, few south-moving seabirds come within range of the seawatcher. Instead, the great majority appear to by-pass the Suffolk coast either by 'bouncing-off' the Norfolk coast at varying tangents (although most birds at Sheringham head east (NBRs, Dare pers.obs.)), or by keeping too far out when rounding the easternmost curve of the coast. Certainly, at Lowestoft all these birds stay outside the offshore sandbanks when heading south and are seldom visible from the cliffs (Dare, pers. obs.). At times of north-west to north gales many individuals of these species are blown towards the Dutch side of the Southern Bight where many Gannets, Kittiwakes and auks head back north upon reaching that coast (Camphuysen & van Dijk 1983). Others evidently continue south and pass through the Dover Strait past Cap Gris Nez where large westerly movements of these three species (among others) occur during NW blows in autumn (Oliver & Davenport 1970). Along the north Kent coast of the outer Thames, at Foreness and Sheppey (Fig. 9), autumn and winter influxes of the same species are observed regularly in association with strong NW-N blows (KBRs, Davenport 1969 and pers. comm.) while strong or gale force NE winds drive many birds deep into the Thames narrows off Canvey (EBRs). Many 'escape' from this natural funnel-trap either by flying east towards the Dover Strait or north-east up the Essex coast, while some Kittiwakes (and skuas) even strike overland south-westwards across Kent (EBRs, KBRs, Davenport, pers. comm.). In Suffolk (as noted earlier in the species accounts) Fulmars, Gannets, Kittiwakes and auks move almost exclusively north during and following NW-NE blows at any time of year. These clearly are extensions of the 'escape' movements witnessed off Essex. They represent displaced individuals returning to their feeding areas in the central North Sea by flying north into the wind in the wake of a depression moving east across the North Sea. Similar recovery or re-orientation behaviour, sometimes on a massive scale, is often reported from north-east England (Wallace & Bourne 1981, Yorkshire Bird Reports), north-east Scotland (Elkins & Williams 1970) and also from the west coast of Holland (Camphuysen & van Dijk 1983). In Suffolk, the small numbers involved suggest that most displaced birds either return north well offshore or (at least in autumn) continue flying south and exit via the Dover Strait. In any event, even the much greater movements off north Norfolk normally represent only a small fraction of the birds potentially involved in any given storm event. Clearly, as one should expect, these 'true' seabirds are expert at avoiding being blown onto a windward shore! The Covehithe records show that spring migration of seabirds close inshore past Suffolk is negligible compared with the large volume and diversity of east-bound 'traffic' through the Dover Strait past Dungeness during March to May (Dungeness B.O. Reports). At Covehithe, apart from some terns, the Gannet was the only species to show evidence at times of true migrants returning north from the Dover Strait. At Dungeness strong easterly passage of Gannets occurs from late February into May. Such birds should then pass close to the north Suffolk coast en route to their northeast coast colonies. This view is supported by some observations made during aerial 33


survey work off the Suffolk coast (Crewe 1994). In March 1993 Gannets were seen flying north on a direct course from Foreness (Kent) towards Orfordness where they turned to follow the coast northwards. Crewe (1994) considered that such behaviour could well explain why seawatches in north Suffolk are far more productive than at Landguard and elsewhere in the south of the county. At other times in spring, the northerly movements of Gannets at Covehithe, like those throughout summer (and of Fulmars), can be interpreted as foraging birds circulating around the Southern Bight. In north Norfolk, by contrast, rather few Gannets are reported in spring, presumably because that coastline is then oriented away from their route north. This overview shows that the patterns of seabird movements around the East Anglian coastline, and in the Southern Bight, are complex. This analysis is a first attempt to collate and synthesise the fragmentary information available. Further progress would require similar analyses for other seawatch sites and the setting up of a co-ordinated observer network. This would need to cover key sites around the Southern Bight and Dover Strait where synchronous sea-watches would be carried out and the observations could then be related to synoptic weather patterns.

Table 1. The total number of seabirds recorded at Covehithe, Suffolk, during early morning watches from 1994 to 1996 (species are listed in order of abundance). Total number Kittiwake Gannet 'Commic' Terns Guillemot/Razorbill Sandwich Tern Fulmar Little Auk Little Gull Arctic Skua Little Tern Great Skua Pomarine Skua skua spp. Sooty Shearwater Manx Shearwater Puffin shearwater spp. Long-tailed Skua

17,105 15,636 5,032 4,826 3,584 3,343 1,032 982 601 255 98 96 62 18 16 14 6 1

Total

52,737

Relative (%) abundance 32.4 29.6 9.5 9.2 6.8 6.3 2.0 1.9 1.1 0.5 0.2 0.2 0.1 0.03 0.03 0.03 0.01 0.002

(Note: 'Commic' Terns = Common + Arctic Terns, not separable.) (Little Tern number refers to passing birds and excludes the local breeding colony.)

34


Table 2. T h e ten largest m o v e m e n t s of Gannets, Kittiwakes and large auks recorded off Suffolk, 1983-93; (wind data for preceding days in parentheses). Gannet

Kittiwake

Large Auks

Movement

Wind

Month

Movement

Wind

Month

Movement

Wind

Month

446N, 80S 324N 273N 242N 225N 223N 158N 15S 158N 143N 140N 17S

N5 (NW6) W N W 6 (NW6) SW6-8 (W5) ESE6 (ESE5) W4-5 (NW6-8) N5-6 (NE6) SE6 (SE5) W N W 4 (W4-5) N N W 5 - 6 (N3) SE5 (ESE5)

Oct Mar Mar Oct Sep Aug Oct Aug Sep Oct

6.000S >3,000N 2.500N 1.500N 200S 1.500N 1.000N 1.000N 775N 600N 600N

SW8-9 (SW8) N6 ( W N W 6 ) SW8 (W5-6) ESE5-6 (NE4) SW5 (S5-6) N N W 5 (NW6) NE6 (NE6) E6 (NE6) NE6 (SSE3) ENE6-8 (NE6-8)

Jan Nov Oct Sep Jan Oct Oct Oct Aug Sep

724N 356N 300 300 280N 272N 250N 250N 230N 210N

E4-5 (NE4-5) N5 (N5) cycl.8 (W6-8) SSE4-5 (ESE4-5) NW5-6 (W5) E6-8 (ENE6) N N W 5 (NW6) S W 3 (NW6) N N W 4 (NNW5) N5 (NW6)

Dec Oct Oct Jan Mar Dec Oct Nov Oct Oct

(Note: wind data estimated from synoptic weather charts and expressed on the Beaufort scale of strength; seabird data from Suffolk Bird Reports.) Table 3. Estimated numbers of seabirds present in the central and southern sectors of the North Sea shown in Figure 9; (from ship-borne transect data collected during 1994 international surveys)

Fulmar Gannet Kittiwake Guillemot Razorbill

1. 2. 3. 4. 5.

maximum 745,000 (Aug.) 102,000 (Nov.) 9 6 7 , 0 0 0 (Aug.) 2,400,000 (Aug.) 2 5 0 , 0 0 0 (Aug.)

minimum 238,000 (Nov.) 27,000 (Feb.) 54,000 (Dec.) 4 0 0 , 0 0 0 (Feb.) 4 5 , 0 0 0 (Feb.)

Feb.* 63,000 3,000 24,000

May 10,000 4,000 13,000

Aug. 59,000 3,000 7,000

Nov. 0 45,000 13,000

Data f r o m Tasker et al. 1987, Dunnet et al. 1990, and C a m p h u y s e n et al. 1995. No separate estimates available for the auks in the Southern Bight. * Refers to February 1993; other m o n t h s are 1994. Separate monthly estimates refer to the Southern Bight. M a x i m u m and m i n i m u m figures are the combined totals for the Central North Sea and Southern Bight.

Acknowledgements I am grateful to Chris D a r b y and David Davenport for helpful c o m m e n t s on the manuscript and also to the latter for discussions and for providing data relating to seabirds along the north coast of Kent. Référencés Camphuysen, C. J. & van Dijk, J. 1983. Seabirds and estuary birds along the Netherlands coast, 1974-79. Limosa 56: 83-230. Camphuysen, C. J., Calvo, B., Durinck, J., Ensor, K., Follestad, A., Furness, R. W., Garthe, S., Leaper, G., Skov, H „ Tasker, M . L. & Winter, C. J. N. 1995. C o n s u m p tion of discards by seabirds in the North Sea. Netherlands Institute for Sea Research Report 1995 - 5, 202pp. Cawston, J. M. & Ling, S. 1988. Seabirds and seawatching in S u f f o l k 1987. Suffolk Birds 37: 7-12. Cawston, J. M . & Ling, S. 1989. Seabirds in Suffolk 1988. Suffolk Birds 38: 21-25. Crewe, M. 1994. Radar tracking of migrant birds. Suffolk Birds 43: 15-17. Dare, P. J. 1996. A u t u m n seabird m o v e m e n t s at Point Lynas, Anglesey during 1976 to 1993. Welsh Birds 1 (3): 29-44. Davenport, D. L. 1969. A u t u m n seabird m o v e m e n t s in the Thames. Kent Bird Report (1969): 84-91. 35


Davenport, D. L. 1987. Seabird movements in Kent, autumn 1987. Kent Bird Report (1987): 93-97. Davenport, D. L. 1991a. A review of seabirds in Kent 1977-1991. Kent Bird Report (1991): 108-113. Davenport, D. L. 1991b. The spring passage of Long-tailed Skuas off North Uist in 1991. Scottish Birds 16: 85-89. Dunnet, G. M., Furness, R. Wâ&#x20AC;&#x17E; Tasker, M. L. & Becker, P. H. 1990. Seabird ecology in the North Sea. Netherlands Journal ofSea Research 26: 387-425. Elkins, N. & Williams, M. R. 1970. Seabird movements in north-east Scotland, 1968 and 1969. Seabird Report 1: 31-39. Fox, A. D. & Aspinall, S. J. 1987. Pomarine Skuas in Britain and Ireland in autumn 1985. British Birds 80: 404-421. Lloyd, C., Tasker, M. L. & Partridge, K. 1991. The Status of Seabirds in Britain and Ireland. T. & A. D. Poyser, London. Nelson, B. 1978. The Gannet. T. & A. D. Poyser, Berkhamsted. Oliver, P. J. & Davenport, D. L. 1970. Large passage of seabirds at Cap Gris Nez. Seabird Report 1: 16-24. Rowley, C. & Jones, P. H. 1980. Bardsey seabird passage project, autumns 1979 and 1980. Part 1. Patterns of species, numbers and ages. Bardsey Observatory Report 24: 44-55. Tasker, M. L., Webb, A., Hall, A. J., Pienkowski, M. W. & Langslow, D.R. 1987. Seabirds in the North Sea. Nature Conservancy Council, Peterborough. 336pp. Wallace, D. I. M. & Bourne, W. R. P. 1981. Seabird movements along the east coast of England. British Birds 74: 417-426. Dr. Peter Dare, Glebe House, Toad Row, Henstead,

Beccles, Suffolk NR34

7LG.


Movements and Abundance of divers off Covehithe, Suffolk, 1994-96 P. J. Dare Introduction The shallow coastal waters off the north coast of Suffolk between Sizewell and Benacre have long been recognised as an important wintering area for Red-throated Divers (Payn 1962, Suffolk Bird Reports). For the 12 winters from 1981/82 to 1992/93 the average peak winter count was 418 divers, ranging between 105 in 1988/89 and 977 in 1982/83 (SBRs). However, virtually nothing has been described concerning their movements and seasonal patterns of occurrence. Elsewhere in East Anglia and in the Thames region, several hundred Red-throated Divers also winter along the Norfolk and Essex coasts (Norfolk and Essex Bird Reports) and in Kent where, in addition, winter movements of up to 1,400 Red-throats sometimes occur (Kent Bird Reports, Davenport 1991). In contrast, both the Black-throated Diver and Great Northern Diver are described as being scarce or very uncommon passage migrants and winter visitors to all these coasts. During a three-year study of seabird movements off Covehithe (Dare 1998) the numbers of divers were also recorded. This paper summarises observations on their annual and seasonal fluctuations in abundance, local and migratory movements, and it assesses the relative importance of this coast for wintering divers. Methods During 1994-96 a total of 625 early morning sea-watches (1,565 hours) and 69 afternoon watches (104 hours) was made from the 30ft high cliff-tops at Covehithe between Southwold and Lowestoft. Full details are given elsewhere in this publication. On each watch divers were identified to species whenever possible and their numbers, group sizes, flight directions, passage rates (numbers per hour) and behaviour were recorded. Ambient conditions such as wind force and direction, sea state, visibility and precipitation were also noted. The near-daily coverage from late summer until late spring spanned the full range of weather experienced during the diver season. For this analysis, most data will be presented as mean monthly values in order to show overall seasonal patterns more clearly by smoothing out short-term variability caused by irregular weather fluctuations and other factors. To correct for varying levels of sea-watch effort the abundance data are expressed also as numbers of divers seen per hour. Their frequency of occurrence in each month is given by the percentage of watches on which divers were observed. Observations 1. Red-throated Diver Gavia stellata At Covehithe, this smallest diver is a common passage migrant and a numerous winter visitor. Feeding birds were usually dispersed widely over the sea out to at least 1-2 miles offshore and regularly commuted to and fro in large flocks, at which times population size could be assessed. There were 21,689 sightings of small divers in flight here during 1994-96, inevitably including many individuals seen repeatedly. Of all sightings 44% were identified positively as Red-throated Divers. The rest were seen in less favourable weather and range conditions, or when moving in flocks too large for every bird to be scrutinised thoroughly. In these circumstances, on probability grounds and unless any obviously large divers were noted, all such birds are regarded as Red-throats for this analysis. Conceivably some Black-throated Divers were overlooked (q.v.). 37


Fig. l a . Red-throated Diver - annual and monthly distribution of 21,689 sightings, 1994-96

Fig. l b . Red-throated Diver - average numbers passing per hour and flight direction, 1994-96

Fig. le. Red-throated Diver - average frequency of occurrence, 1994-96

38


The averaged seasonal pattern of Red-throated Diver occurrence (Fig. la-c) shows autumn passage birds first appearing in late August or mid-September after which numbers built up steadily to a peak in January before falling rapidly through early spring with stragglers well into May. Extreme dates were August 27th and May 28th. The winter peak varied in timing from year to year, being in January of 1994 and in February of 1995 but in the colder weather of 1996 it was spread over both months. The highest individual morning counts in each winter were: 2,724 on January 23rd 1994, 646 on February 9th 1995 and 1,513 on February l l t h 1996. Monthly peak counts were: Jul 0

Aug 1

Sep 8

Oct 9

Nov 385

Dee 530

Jan 2724

Feb 1513

Mar 920

Apr 107

May 13

Jun 0

In autumn, there was a trickle of passing divers, both north and south, until late November or early D e c e m b e r when the first prominent southerly passages or arrivais became evident, e.g. up to 368 in 3.5 hours. Typically, the divers flew in small groups throughout much of the morning and usually at m e d i u m or long ranges in clear conditions with little wind; some would pause briefly before moving on. In winter, the daily feeding m o v e m e n t s were sometimes on a spectacular scale when, presumably, most or all of the 'resident' population off the north Suffolk coast was involved. These population shifts usually took place within 0.5-2 hours of sunrise, lasted for 0.25-1.5 hours, and comprised up to 300-400 divers. Birds generally flew low and in the same direction f r o m 0.25-1 mile offshore. Very f e w were seen during occasionai afternoon watches. Several massive fly-pasts occurred, e.g. 596 in 10 minutes , 6 0 3 in 15 minutes and 1,380 in 50 minutes. Divers often landed, or took off to join a movement, but most continued for 1-2 miles past Covehithe until out of sight. On February 21st 1992 I saw 146 fly north past Pakefield, s o m e five miles north of Covehithe. In Kent, similar early morning shifts occur frequently off Foreness and Dungeness (D. Davenport, in litt.). The direction of these winter m o v e m e n t s on any particular morning seemed to be governed m o r e by wind direction than by tidal conditions, though the latter doubtless played some part at times. Flocks tended to fly into the wind even though 9 2 % of the 24 largest m o v e m e n t s (>100 divers) occurred in light or moderate breezes, and the rest with fresh winds. Thus, of ten southerly movements, 7 0 % coincided with a southerly wind component, 10% with a northerly, 10% with offshore westerly and 10% with an onshore easterly. By contrast, for 14 northerly movements, 4 3 % were with a northerly wind component, only 7% with a southerly, and the rest were in offshore westerlies. In Denmark, and in the Dover Strait, such early morning movements are considered likely to be compensating for tidal drift (Meltofte and Kiorboe 1973, D. Davenport, in litt.). A phĂŠnomĂŠnal southerly movement of 2,724 divers occurred between about 09.30 and noon on January 23rd 1994. In addition to a continuous stream of small groups, several large and diffuse puises occurred, each involving several hundred birds, in the largest of which 515, 569 and 462 divers passed in 5-10 minute periods. Most birds flew at some 50ft above the water and 0.5-1 mile offshore with clear visibility and a fresh west wind, following a light westerly here the previous morning. The synoptic weather charts show that a westerly gale was blowing off the east coast north of The Wash on January 22nd and had veered to W N W gale/severe gale in that area by noon on 23rd. This suggests that the divers originated from off, or to north of, The Wash; surprisingly, no unusual numbers were reported from the Norfolk coast at that time (NBRs). The onset of spring departures f r o m the winter gatherings varied in its timing. It was indicated best by numerical trends rather than f r o m visible m o v e m e n t s themselves due to the complicating factor of the local foraging flights. M a j o r


Fig. l d . Red-throated Diver - n u m b e r s passing per hour and flight direction of 8,292 sightings, 1994 No./hr 120-1 100

60 40

â&#x20AC;˘

L J

F

M

A

M

v

J

A

S

O

1I N

D

month Hnorth

[ S j south

Fig. l e . Red-throated Diver - n u m b e r s passing per hour and flight direction of 3,739 sightings, 1995

^north

[^Isoutti

Fig. If. Red-throated Diver - n u m b e r s passing per hour and flight direction of 9,658 sightings, 1996 no./hr 150

40


émigration periods could occur any time from late January into early March depending on local weather conditions. In 1994, few divers remained into February (Figs. la, d) following a mild January in which mean air temperature in East Anglia was 2°C above normal (Met. Office Weather Log ). Large northerly movements totalling 504 divers during January 26th-28th that year could well have been mostly departing birds. In 1995, both January and February were very mild (1.5°C and 4°C above normal). Diver numbers at Covehithe throughout that winter were much lower than in the other two and peaked in February (Figs. 1 a, e) although virtually ail had left by March. In 1996, by contrast, when late January and February were cold (some 2°C below normal) diver numbers were high (Figs. la, f) and remained so into March, which also was a cold month. The first ten days in March 1996 appeared to be the main departure period that year; aggregate sightings then amounted to 2,313 flying north with only 271 south and few seen thereafter. Fig. 2. Red-throated Diver - spring sightings in ten-day periods from March 11 th. 1994-96 number 800

600

400

200 Mari

2

3

Apri

2

3

May1

2

3

10-day period X-south

^north

Subsequently, spring passage of divers from more southerly winter haunts was inferred from the prédominance of north-bound birds after mid-March and especially in April and May. The pattern of these sightings is aggregated over the three years and shown by 10-day periods in Fig. 2 with the winter data removed (cf. Fig. la). A peak of northerly passage is indicated in late March and early April. Most divers that moved south in March were in 1996 and were probably late wintering birds whose departures had been delayed by that cold winter, as noted above. From mid-April through May the passage was very light even though divers still passed north on nearly 40% of May mornings (Fig. le). Some of the May birds were still in nonbreeding plumage. The estimated total numbers of passage Red-throats observed during April and May were: 115-135 in 1994, 15-20 in 1995 and 260-300 in 1996. The weather on spring passage mornings generally was bright, often with clear visibility and with light winds, though sometimes there were moderate or fresh northeast winds accompanied by moderate haze. Divers passed Covehithe from around sunrise and sometimes continued in a steady trickle through the morning; occasionai birds were noted in the afternoon. They flew singly or in very small groups at heights up to lOOft or more and often in a very fast and direct manner, quite différent from the winter flights. Most were at medium or long ranges and continued north until lost to sight. Some landed briefly while, especially later in the morning, others might rest longer (at least until the end of the watch). Virtually ail divers flew parallel to the 41


coast though some distant birds could be seen approaching high from the south-southeast, i.e. from the direction of the Dover Strait. On three occasions in March and Aprii 1996, some (eight in total) of the nearest divers, including one just off the sea, were observed to turn offshore and head out north-easterly until lost to view; one climbed to a considĂŠrable height. 2. Black-throated Diver Gavia arctica The 40 individuate identified comprised only 0.18% (1 in 588) on average of ali the divers seen off Covehithe. Their relative abundance varied seasonally, however, being most frequent in autumn (0.93% or 1 in 107 divers) and scarcest in winter (0.04% or 1 in 2,476). These values will be slight underestimates because 32 probable Blackthroats were also recorded, some of which (given more favourable conditions) undoubtedly would have been confirmed. Even if these are included, then the maximum likely winter proportion of Black-throats is unlikely to have exceeded 0.08% or 1 in 1,238 divers during 1994-96. In which case the winter assembly of divers off the north Suffolk coast could be expected at times to have included one or two Blackthroats, an estimate in good agreement with the SBR records for 1983-93. Fig. 3a. Black-throated Diver - annual and monthly distribution of 40 sightings, 1994-96

There were 19 positive sightings in autumn (between September 13th and November 21st), six in winter (December 7th to February 9th) and 15 in spring (March 1 lth to May 22nd). Ail but two of the birds were in flight. The records (Fig. 3a-b) show distinct passage periods in autumn, when 84% of birds were flying south, and in spring when ail were heading north. The autumn passage peak in November is shown also by the SBR records of offshore Black-throats (Fig. 3c). The latter, however, do not indicate any spring passage, probably because few early morning seawatches were undertaken at that season. At Covehithe more than half of the birds passed within the first two hours after sunrise and in fair weather. Neither passage was obviously correlated with particular wind conditions although most birds passed in light or moderate winds and none when stronger than fresh (force 5). Of the 19 autumn birds, nine appeared with winds from NW-NE and seven with W-SW winds, while five of the 15 spring divers passed in NW-NE, seven in W-SW and only three with onshore E-NE winds. Ail but three of the 1994-96 sightings were of single Black-throats, the exceptions being: two south together on November 27th 1994, a group of four south on November 13th 1994, and a group of three plus two singles north on Aprii 19th 1994. Many 42


individuals were flying close to single Red-throated Divers or were a m o n g a group of the smaller divers; one accompanied a Great Northern Diver. Fig. 3b. Black-throated Diver - average n u m b e r s passing per h o u r and flight direction, 1994-96 no./hr 0.08

0.06

0.04

0.02

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Fig. 3c. Black-throated Diver - monthly distribution of records published in Suffolk Bird Reports, 1983-93 number 20

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month

3. Great N o r t h e r n Diver Gavia immer This was by far the scarcest of the three divers during 1994-96, with the 14 identified individuals (Fig. 4a) comprising only 0.06% (1 in 1,667) of ail divers seen. It was rare in winter (1 in 14,855) and generally was outnumbered at least 2.9 to 1 by Blackthroated Divers (cf. 3.0 to 1 in S B R s during 1983-93). There were ten autumn sightings (between October 16th and N o v e m b e r 27th), one in early winter (December 16th) and three in late spring (May 9th and 18th). A distinct passage peaked in N o v e m b e r as is shown also by the S B R records of offshore birds (Fig. 4c). Five of the 11 autumn Great Northerns at Covehithe occurred during N W - N E winds and four with W - S W winds, ail light to fresh in strength. Most birds were flying north (Fig. 4b). T h e three spring individuals coincided with light N W - N E breezes and included two heading north together on M a y 18th 1994. 43


Fig. 4a. Great Northern Diver - annual and monthly distribution of 14 records, 1994-96 number

A

S

O

N

JL

F

M

A

M

J

month • 1994

• 1996

•-•-1995

Fig. 4b. Great Northern Diver - average numbers passing per hour and flight direction, 1994-96

Fig. 4c. Great Northern Diver - monthly distribution of records published in Suffolk Bird Reports, 1983-93

J

A

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month 44


Discussion In winter Red-throated Divers are found close inshore more or less continuously down the east coast of Britain including the greater Thames area. They are also rather mobile in response to local weather conditions and can feature prominently in weather-induced longshore movements of seabirds (Parrack 1986). At Covehithe during 1994-96 their peak winter numbers ranged between 500 and 1,500, and thus were above the long-term (1982-93) average of 418 birds for the north Suffolk coast (SBRs). The highest Covehithe counts presumably represented all (or virtually all) of the divers which routinely flight to and fro over varying distances between, or maybe beyond, Sizewell and Benacre. The extraordinary southerly movement of 2,724 divers on January 23rd 1994 differed totally in character from local feeding movements. It is perhaps best interpreted as an extreme example of a weather-induced displacement of birds from further up the east coast, and was triggered apparently by W - N W gales north of The Wash. Large winter movements of Red-throated Divers are not so unusual in east Kent where 1,000-2,000 may undertake shuttle movements through the Dover Strait past Foreness or Dungeness in response to NW-NE winds blowing in the southern North Sea (KBRs, Davenport 1991). An exceptional event occurred during February 21st to 22nd 1996 when 2,740 and 526 divers flew east at Dungeness after two days of N-NE gales; evidently a compensatory movement for displacement (Davenport, in litt.). Divers from the Dutch and Belgian coasts could be major components in such passages. In Norfolk, weather movements are usually much smaller but notable flights occurred in January 1992 when 711 flew north at Walcott on 18th and 820 east off Sheringham on 29th during moderate to fresh W N W and easterly winds respectively. By comparison, the record count for the Palearctic was made in Denmark where 3,000-5,000 divers (predominantly Red-throats) were seen migrating north up the west coast on May 1st 1966 (Meltofte & Kiorboe 1973) though this is not cited in BWP (Cramp & Simmons 1977). More recently, in Scotland an assembly of over 1,500 Red-throated Divers was observed in the Moray Firth in October 1982 (Parrack 1986). The quasi-resident Suffolk gathering of Red-throated Divers is currently larger than any others found regularly in East Anglia. In Norfolk and Essex peak winter counts typically range between 100-300 birds, with respective maxima of 400 and 380 (NBRs, EBRs). In Kent the average winter peak count over a longer period (1978-91) was 763 on the north coast and 482 at Dungeness (Davenport 1991). Elsewhere in Britain, some Scottish eastern firths hold 100-350 Red-throats in autumn but only Cardigan Bay, with 400-1,000 in recent winters (WeBS Annual Reports), matches the Suffolk coast in importance. Given that the total winter population of Red-throats in Britain is estimated variously at 12,000-15,000 birds (Parrack 1986) or as low as 4,300-5,400 (Danielsen et al. 1993), it is clear that a significant proportion winters off our coast. The Suffolk divers require an abundant winter food supply of small fish which occur in locations sheltered from the worst effects of North Sea storms. Red-throats forage in shallow (< 30ft deep ) waters, such as those off north Suffolk inshore of the Dunwich Bank, and take mainly herring, sprat and cod as well as sand-eels, gobies and other small species (Cramp & Simmons 1977). The first two species are most probably the staple diet of our local divers. Sprats are often abundant in winter throughout the Thames areas, especially around Sizewell, while young herring can also be numerous in certain years and mix with sprats to form shoals of whitebait (per M A F F Fisheries Laboratory, Lowestoft). Many other fishes occur but in smaller quantities and are thus likely to be relatively unimportant in the diet. Most Red-throated Divers that winter off the east coast are from breeding


populations in northern Scotland and Scandinavia with some from Iceland. The flocks in the Moray and other firths in October are thought to be direct immigrants from Scandinavia (Parrack 1986). However, few reach Suffolk before mid- or late November, the adults evidently having stopped off en route south to undertake their post-breeding moult (during which they become flightless) sometime between late September and December (Cramp & Simmons 1977). In western Denmark, a significant fall in autumn passage numbers from late October until late November is said to coincide with the main moult period (Meltofte & Kiorboe 1973). The spring migration of Red-throated Divers past Covehithe, especially in March, was difficult to distinguish from departures of local wintering birds. Divers can also migrate at night (Cramp & Simmons 1977). In Aprii and May a rather sporadic passage, of up to 300 divers, was observed - far fewer than those (up to 4,600) observed moving east past Dungeness each spring (Dungeness Bird Observatory Reports). There, after the winter flocks have left, usually in February, but in the first week of March after a cold winter, a conspicuous spring passage produces up to 630 Red-throats on peak day s in March and 230 in early Aprii (Davenport 1990). In contrast with early morning movements in winter, most spring birds in Kent pass later in the day, between 09.00-15.00h, whereas at Covehithe very few were seen in late mornings or afternoons. Evidently, once in the southern North Sea they either move up the Continental side or tend to keep too far off our coast to be observed. Regarding the Black-throated Diver, my observations confirm it to be a scarce visitor to the Suffolk coast. Probably no more than one or two birds are generally present in winter among the numerous Red-throated Divers. The small autumn passage peaking in November agréés with earlier Suffolk offshore records (SBRs) and with the species' status elsewhere in the région. The timing of the few spring birds at Covehithe falls within the period of the prominent easterly migration past Dungeness. At that site, 75-125 Black-throats are recorded each spring and 10-20 on peak days between early Aprii and early May (DBORs). Great Northern Divers were even scarcer at Covehithe, their few sightings conforming with expected passage times. The three late spring birds in May agree with experience at Dungeness where up to nine Great Northerns have occurred in recent springs and of which nearly half have been in May. Finally, from a conservation viewpoint, any site that supports 750 or more Redthroated Divers is classed as being of international importance while the équivalent criterion for national (UK) importance is 50 divers (WeBS Annual Reports). For the Black-throated Diver the national limit is seven birds. Clearly, the Suffolk Redthroated Diver concentration is internationally important in some winters apart f r o m being of great national significance. It therefore merits appropriate protection against oil spillages and any potentially damaging activities that might be proposed along this stretch of the Suffolk coast. Acknowledgements I am grateful to Derek Eaton and Graham Pickett for information on local fish stocks, and to Chris Darby and David Davenport for helpful comments on the manuscript. The last observer also kindly provided information on divers in Kentish waters. Postscript In the 1996-97 winter, the largest local feeding movement yet seen at Covehithe occurred on February 5th 1997 when 1,735 Red-throated Divers flew north early on a calm morning. 46


Référencés Cramp, S. & Simmons, K. E. L. 1977. Handbook of the Birds of the Western Palearctic. Vol.l. Oxford. Danielsen, F., Skov, H. & Durnick, J. 1993. Estimâtes of the wintering population of Red-throated Diver Gavia stellata and Black-throated Diver Gavia arctica in northwest Europe.Proceedings of7th Nordic Congress of Ornithology 1990: 18-24. Dare, R J. 1998. Seabird movements and abundance off Covehithe, Suffolk, 1994-96. I. Fulmar, Gannet, Kittiwake, Guillemot and Razorbiil. Suffolk Birds 46. Davenport, D. L. 1990. Spring seabird, wildfowl and wader passage at Dungeness. Dungeness Bird Observatory Report 1990: 36-40. Davenport, D. 1991. Review of seabirds in Kent 1977-1991. Kent Bird Report 1991: 108-113. Meltofte, H. & Kiorboe, T. 1973. The occurrence of divers Gaviidae at Blavand, 1963-71.(In Danish). Dansk Ornithologisk Forenings Tidsskrift 61: 109-114. Parrack, J. D. 1986. Red-throated Diver. pp.34-35, In: Lack, P. The Atlas of Wintering Birds in Britain and Ireland. T. & A.D.Poyser, Calton. Payn, W. H. 1962. The Birds of Suffolk. Ipswich. Waters, R. J. & Cranswick, P.A. 1993. The Wetland Bird Survey 1992-93: Wildfowl and Wader Counts. BTO/WWT/RSPB/JNCC, Slimbridge. Dr. Peter Dare, Glebe House, Toad Row, Henstead,

Red-throated

47

Diver

Beccles, Suffolk. NR34

7LG

Suffolk Birds 1996 Part 1  

Volume 46

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