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Numbers of wintering gulls in the United Kingdom, Channel Islands and Isle of Man: a review of the 1993 and previous Winter Gull Roost Surveys Niall H. K. Burton, Andy J. Musgrove, Mark M. Rehfisch, Anna Sutcliffe and Ray Waters Steve McQueen ABSTRACT This paper summarises the January 1993 Winter Gull Roost Survey and evaluates the results of this and the four previous surveys of wintering gulls, carried out in 1953, 1963, 1973 and 1983. In total, 2,594,491 gulls were counted in Great Britain during the 1993 survey: 1,263,208 at inland sites and 1,331,283 on the coast, comprising an estimated 1,682,385 Black-headed Gulls Larus ridibundus, 429,331 Common Gulls L. canus, 60,830 Lesser Black-backed Gulls L. fuscus, 376,775 Herring Gulls L. argentatus, 43,108 Great Black-backed Gulls L. marinus and 2,062 gulls of other species.A further 19,030 gulls were counted in Northern Ireland, 3,853 in the Isle of Man and 8,477 in the 376 © British Birds 96 • August 2003 • 376-401 Wintering gulls in the UK Channel Islands. Using thresholds of 1% of the respective minimum British populations, 22 sites of potential national importance were identified for Black-headed Gull, 28 for Common Gull, 19 for Lesser Black-backed Gull, 19 for Herring Gull and 20 for Great Black-backed Gull.Areas in which gulls were counted varied between surveys, but gulls at inland sites in England were counted in all five surveys.All five ‘key’ species increased at inland sites in England between 1953 and 1993, in particular Lesser Black-backed Gulls. The increase in wintering gull numbers in Great Britain has probably led to greater numbers of gulls using individual roosts and more roost sites being occupied. More recently, however, there have been some declines, notably of Herring Gulls. his paper presents the results of the last aghan & Coulson 1977; Lloyd et al. 1991). More UK-wide survey of winter gull roosts, recently, the growth in the UK breeding popula- Tcarried out in January 1993, and pro- tions of Lesser Black-backed and Great Black- vides minimum population estimates for five backed Gulls has slowed, while the breeding species: Black-headed Gull Larus ridibundus, populations of Black-headed, Common and Common Gull L. canus, Lesser Black-backed Herring Gulls have declined (Lloyd et al. 1991; Gull L. fuscus, Herring Gull L. argentatus and Tasker et al. 1991; Gibbons et al. 1993; Gregory Great Black-backed Gull L. marinus. Four pre- et al. 2002). Black-headed, Common, Lesser vious surveys (Hickling 1954, 1967, 1977; Black-backed and Herring Gull are all included Bowes et al. 1984) suggested that numbers of on the Amber List of ‘Birds of Conservation wintering gulls increased between the 1950s and Concern’ in the UK owing to the decline and/or 1970s, and certainly there is considerable evi- relatively small size of their breeding popula- dence that breeding populations, particularly of tions (Gregory et al. 2002). The Common Gull Lesser Black-backed and Herring Gulls, rose is also listed as a Category 2 ‘Species of Euro- during the twentieth century until the 1970s. pean Conservation Concern’ owing to a mod- (Harris 1970; Chabrzyk & Coulson 1976; Mon- erate decline in its numbers in Europe, which is /Windrush David Tipling 267. Gulls Larus settled at roost, Bough Beech Reservoir, Kent. British Birds 96 • August 2003 • 376-401 377 Wintering gulls in the UK /Windrush David Tipling 268. Black-headed Larus ridibundus and Common Gulls L. canus disturbed from roost. It is easy to appreciate the potential hazard that large gull roosts, or the flight lines to and from roosts, may pose to aircraft the stronghold of this species (Tucker & Heath destruction of eggs was used to reduce numbers 1994). of Lesser Black-backed and Herring Gulls, The increase in gull numbers during the which apparently threatened other nesting twentieth century is thought to have stemmed seabirds (Duncan 1978; Wanless et al. 1996; from a reduction in human persecution Finney et al. 2003). It is probable that such poli- (hunting and egg-collecting) coupled with cies contributed to regional declines of these greater food availability (Spaans 1971; Lloyd et species in the 1970s and 1980s (Coulson 1991; al. 1991). The widespread use of rubbish tips Lloyd et al. 1991). (Horton et al. 1983) and outfalls (Ferns & While it can be argued that there is a need to Mudge 2000) has brought gulls back into con- control gull numbers in certain areas, it is also flict with humans, mainly because of concern important to recognise their conservation status about the spread of disease (Fenlon 1981, 1983; in the UK. The UK holds considerable propor- Benton et al. 1983; Butterfield et al. 1983; tions of the European populations of these Coulson et al. 1983a; Fricker 1984; Monaghan species (Hagemeijer & Blair 1997), most et al. 1985; Ferns & Mudge 2000). In particular, notably 71% of the breeding population of one there are concerns that gulls may act as carriers subspecies of Lesser Black-backed Gull, L. f. of salmonella between these sources and the graellsii (Stroud et al. 2001). Large numbers of inland water reservoirs on which they roost at gulls from Scandinavian and other west Euro- night. Concern over such health risks, the pean breeding populations winter in the UK, hazards posed by gulls to aircraft (Rochard & particularly in eastern Britain, while birds of Horton 1980; Gosler et al. 1995; Milsom & British origin are more predominant in the west Horton 1995), and the possible effects of larger (Stanley et al. 1981; Coulson et al. 1983b, 1984a, numbers of gulls on wetland and coastal habi- 1984b; Cramp & Simmons 1983; Horton et al. tats, and on other seabirds and waterbirds, has 1983, 1984; Monaghan et al. 1983; Christmas et prompted efforts to disturb gulls from favoured al. 1986; MacKinnon & Coulson 1987; sites or to reduce the size of their colonies. For Wernham et al. 2002). example, Lesser Black-backed Gulls have been In order to conserve these species properly, it culled under licence at Abbeystead, Lancashire, is essential that the extent of both breeding and partly in order to prevent contamination of a wintering populations are known and that sites local reservoir (Wanless & Langslow 1983), which are important for individual species are while on the Isle of May, Fife, the repeated identified. This paper presents minimum winter 378 British Birds 96 • August 2003 • 376-401 Wintering gulls in the UK population estimates for the five key species, for the majority of coastal roosts. inland and coastal sites, at both regional and The 1993 survey covered coastal and inland national levels, based on the 1993 survey. We sites in Great Britain, Northern Ireland, the Isle also provide amended threshold levels in order of Man and the Channel Islands. Observers to identify sites of potential national impor- were asked to count or estimate the numbers of tance for wintering gulls. Minimum population gulls at roosts around sunset between 21st and estimates are compared, where possible, with 31st January 1993, preferably on 22nd or 23rd those from previous Winter Gull Roost Surveys. January. There are a number of sources of potential Field methodology of the 1993 survey and error in counting gulls at roosts, and to help factors affecting count accuracy minimise these, suggested guidelines were pro- The January 1993 Winter Gull Roost Survey fol- vided for observers. Firstly, as noted in previous lowed the same methods used by surveys in surveys, counts of birds flying into roosts are 1953, 1963, 1973 and 1983 (Hickling 1954, typically more accurate estimates than counts of 1967, 1977; Bowes et al. 1984). These previous birds already settled, particularly if birds roost surveys varied in their coverage. In January on choppy water. Furthermore, at large roosts, 1953, inland (and some coastal) roosts in it is necessary to have several observers sta- England and parts of Scotland were surveyed tioned around the site to simultaneously cover (Hickling 1954). The next survey, again pri- birds arriving on different flight lines so that marily of inland sites in England, was planned overall numbers are not underestimated. for December 1962 and January 1963, but The difficulties of identification will also owing to the exceptionally severe weather that affect the accuracy of counts of individual winter, the majority of counts were undertaken species. In some cases, it may be necessary to in December 1963 (Hickling 1967). The January estimate the total numbers of each species from 1973 survey included inland roosts in Wales the proportions of each in part of a roost or on (Hickling 1977), while the January 1983 survey a flight line. Where this was not possible, was the first to cover the whole of Great Britain observers in the 1993 survey instead provided (and the Channel Islands, but not the Isle of information on the numbers of unidentified Man), and was also the first attempt to cover ‘small’ gulls (Black-headed and Common Gulls) Robin Chittenden 269. A mixed group of Black-headed Larus ridibundus, Common L. canus and Herring Gulls L. argentatus, Cromer, Norfolk, February 1996. Gulls arriving at roosts in mixed groups like this are more difficult to count than roosts where a single species predominates.Where birds arrive in large mixed groups it may be possible only to estimate the total numbers of gulls involved, and the relative proportions of ‘small’ (Black-headed and Common) and ‘large’ gulls. British Birds 96 • August 2003 • 376-401 379 Wintering gulls in the UK and unidentified ‘large’ gulls (Lesser Black- estimate of species A = count of small gulls × backed, Herring and Great Black-backed Gulls) pspecies A counted, in addition to any counts of individ- where pspecies A = the number of species A uals identified to species.

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