Suffolk Birds 1993 Part 1

each colony has a reasonably well defined area of occurrence after post-breeding dispersal.

However, it is unknown at present whether birds from the Orfordness colony winter in Suffolk or move elsewhere.

Lesser Black-backed Gull Larus fuscus Up until fairly recently, the Lesser Black-backed Gull was rarely seen in Suffolk during the winter but migration patterns changed dramatically during the period covered by the Winter Gull Roost Census (Lack 1986). In Suffolk, a similar change has been observed with numbers not only increasing during the winter but also during the summer with the establishment of the Orfordness breeding colony in the late 1960s. (Payn 1978). The colony has undergone a very large increase during the last 15 years, but it has only been in the last decade that a marked change has been observed in the species' wintering behaviour.

In Suffolk, wintering Lesser Black-backs are mostly confined to the inland roost at Lackford Wildfowl Reserve where around 82% of the total found in the County during the 1993 census occurred. Elsewhere numbers are much lower with the remaining 18% scattered throughout the other roost sites. The dominance of Lackford as a winter roost is no doubt due in part to the presence of the nearby landfill site as a source of food. It is also likely that birds have spread further east from other wintering areas in central England; Lack (1986) states that wintering Lesser Black-backs are more commonly found inland, with freshwater roost sites being very important.

The change in the wintering behaviour of this species has been much more pronounced than any changes in the breeding population during the last decade. The Orfordness colony, now established, has remained relatively stable at 8,500 pairs for the last ten years, as documented in Suffolk Birds. However, the wintering numbers have increased dramatically from a handful of individuals in 1983 to the estimate of 265 in the 1993 census. A steady increase in the number of recorded wintering individuals can also be traced through the County bird reports for the last ten years. Ringing recoveries show that the majority of Suffolk's breeding population winters on the north-west African coast so the origin of the birds wintering in the County is, as yet, a mystery. It is most likely that these birds are originating from further north on the Continent, although the most northerly populations L. f . fuscus habitually migrate south-eastwards to winter in the Middle East and East Africa (Grant 1986).

Great Black-backed Gull Larus marinus Although the wintering population of this species is well below that of the three commonest species, twice as many Great Black-backs were found during the census as Lesser Blackbacks. The presence at Lowestoft Harbour of almost three-quarters of the total wintering population of this species in the County is to be expected, given its strong preference for maritime roost sites with only 30% occurring away from the coast.

It is the size and aggresive nature of the Great Black-backed Gull that makes it such a dominant component of any roost or feeding flock. As discussed previously, offal is not so readily available within the Lowestoft Harbour complex as was once the case; with this in mind, the presence of fairly large numbers of this species is perhaps surprising, although the dominance of this species may help to explain the relative scarcity of Herring Gulls at the site by way of competitive exclusion. This may also account for the larger number of Herring Gulls at Sizewell where Great Black-backs are less frequent.

The river estuaries and inland sites are far less important for this species than the immediate coast with the Orwell and Stour estuaries and Lackford Wildfowl Reserve all attracting around 50 individuals during the census. Data from the Birds of Estuaries Enquiry (BoEE) counts reveal that the Aide/Ore estuary is the most important estuary in the County for this species; however; this estuary was not included in the roost census in 1993.

This species does not breed in Suffolk and the wintering population is probably a mix 11