Abstract from BTO Research Report No. 456:

A.N. Banks, N.H.K. Burton, J.R. Calladine & G.E. Austin (2007)

Winter Gulls in the UK: population estimates from the 2003/04 Winter Gull Roost Survey ISBN: 1-904870-93-7

Executive Summary

1. This report provides population estimates derived from the 2003/04-2005/06 Winter Gull Roost Survey for the five principal species that winter in the UK, the Channel Islands and Isle of Man: Black-headed Gull Larus ridibundus, Common Gull L. canus, Lesser Black-backed Gull L. fuscus, Herring Gull L. argentatus and Great Black-backed Gull L. marinus.
2. The survey provides the first comprehensive estimates of winter gull populations in the UK, derived from counts undertaken at roost sites. Estimates were derived by combining counts from ‘Key Sites’ and estimates for the numbers of birds wintering away from these sites derived from stratified sampling. The survey covered the constituent countries of the United Kingdom (England, Northern Ireland, Scotland, Wales), plus the Crown Dependencies of the Channel Islands and Isle of Man.
3. Survey sites were categorised into a number of types. Inland and Coastal ‘Key Sites’ were major roosts identified from past surveys and bird reports as holding >1,000 gulls. Sample Random Inland Tetrads and Random Coastal Stretches were surveyed in order to estimate (through bootstrapping techniques) the numbers of birds wintering away from Key Sites both inland and on the coast.
4. The survey was run over a period of three winters between 2003/04 and 2005/06, with sites primarily covered by volunteers, with additional cover from professional staff. Sites were counted at dusk in January. Forms were returned for 1,460 sites (69%) of a total of 2,116 sites identified.
5. A total of 2,440,681 gulls of 13 species were recorded during the main counts used to produce population estimates: 1,222,345 inland and 1,218,336 on the coast. In addition to the five main species, other species counted were: Mediterranean Gull Larus melanocephalus, Little Gull Larus minutus, Ring-billed Gull Larus delawarensis, Caspian Gull Larus (argentatus) cachinnans, Yellow-legged Gull Larus michahellis, Iceland Gull Larus glaucoides, Glaucous Gull Larus hyperboreus and Kittiwake Rissa tridactyla, though the sum total of these was only 1,801.
6. These counts were then used to produce estimates (with confidence limits) of the five principal species wintering in the UK (Table 3.2.2) The most abundant species was Black-headed Gull: 2,155,147 were estimated to occur in Great Britain (1,854,876 in England, 199,682 in Scotland and 100,836 in Wales), 44,336 in Northern Ireland, 7,565 in the Channel Islands and 1,753 in the Isle of Man.
7. Common Gull was the next most abundant species: 695,833 were estimated to occur in Great Britain (469,863 in England, 200,296 in Scotland and 25,133 in Wales), 9,559 in Northern Ireland, 7,702 in the Channel Islands and 35 in the Isle of Man.
8. Similar estimates were calculated for Herring Gull: 729,801 were estimated to occur in Great Britain (362,821 in England, 273,058 in Scotland and 93,613 in Wales), 13,559 in Northern Ireland, 10,828 in the Channel Islands and 10,106 in the Isle of Man.
9. 124,654 Lesser Black-backed Gulls were estimated to winter in Great Britain (114,369 of those in England, just 6,510 in Scotland and 3,838 in Wales), though only 459 were estimated to occur in Northern Ireland, 14 in the Channel Islands and seven in the Isle of Man.
10. Great Black-backed Gull was the least abundant species, with 75,860 estimated in Great Britain (53,361 in England, 18,113 in Scotland and 4,365 in Wales) and a further 750 in Northern Ireland, 732 in the Channel Islands and 566 in the Isle of Man.
11. Using the population estimates, new thresholds of national importance in Great Britain were calculated: Black-headed Gull 20,000, Common Gull 7,000, Lesser Black-backed Gull 1,200, Herring Gull 7,300 and Great Black-backed Gull 760. The estimates suggest that, in winter, Great Britain holds 51% of Black-headed Gulls, 40% of Common Gulls, 23% of Lesser Black-back Gulls (graellsii race), 23% of Herring Gulls (argentatus and argenteus races) and 17% of Great Black-backed Gulls, in relation to estimated international populations. Individual sites of potential national and international importance for gulls in both Great Britain and Northern Ireland are highlighted.
12. Survey methods and coverage are evaluated, and recommendations for future monitoring and survey outlined. These are:

• that annual data are collated from Key Sites to enable better indexing of species’ UK population;

• that further count data should also be collected at Key Sites in order to identify those worthy of statutory designation. Caution should be adopted in selecting sites where single counts provide the only data source; such counts should facilitate targeting of sites for increased coverage and better assessment of the regularity of site use, so as to improve confidence in selection of the most important roosts in national and international contexts.

• that the Winter Gull Roost Survey is repeated at intervals of nine years (thus next in 2012/13-2014/15) so as to provide regular updates of the UK wintering populations of Black-headed Gull, Common Gull, Lesser Black-backed Gull, Herring Gull and Great Black-backed Gull.

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