Abstract from BTO Research Report No 277:

N.H.K. Burton, A.J. Musgrove, M.M. Rehfisch & A. Sutcliffe (2002))

Winter Gull Roosts in the United Kingdom in January 1993
With Recommendations for Future Surveys of Wintering Gulls
ISBN 1-902576-54-3

Executive summary

1. This report is in two main parts. The first (chapters 1-4) summarises the results of the January 1993 Winter Gull Roost Survey and makes comparison with past surveys undertaken in 1953, 1963, 1973 and 1983. The second (Chapter 5) provides recommendations for future surveys of the UK’s wintering gull populations.

2. The report provides minimum population estimates for 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, for inland and coastal sites, both at regional and national levels, based on the 1993 survey. These estimates represent the sums of the estimated numbers of birds counted of each species. No attempt has been made to estimate the numbers of gulls in areas not covered by the survey.

3. In total, 2,599,333 gulls were counted in Great Britain during the January 1993 Winter Gull Roost Survey, 1,268,048 at inland sites and 1,331,285 on the coast. This total included an estimated 1,679,341 Black-headed Gulls, 428,441 Common Gulls, 60,757 Lesser Black-backed Gulls, 374,358 Herring Gulls, 42,990 Great Black-backed Gulls and 13,446 of other species. A further 19,030 gulls were also counted in Northern Ireland, 3,853 in the Isle of Man and 8,477 in the Channel Islands

4. Black-headed Gulls were proportionally more common at inland sites, whilst Herring Gulls were conversely more common on the coast. In relation to the total numbers of gulls counted, Black-headed Gulls were most numerous in England, Common Gulls most numerous in Scotland, Lesser Black-backed Gulls least common in Scotland and most common in Wales, and Herring Gulls more common in Scotland than in England. Great Black-backed Gulls were rather more evenly distributed.

5. The following thresholds, calculated as 1% of the minimum British population, are recommended as broad indicators of the national importance of sites for wintering gulls: Black-headed Gull – 17,000, Common Gull – 4,300, Lesser Black-backed Gull – 610, Herring Gull – 3,800 and Great Black-backed Gull – 430.

6. Using these thresholds, 22 sites would qualify as nationally important for Black-headed Gull, 23 for Common Gull, 19 for Lesser Black-backed Gull, 19 for Herring Gull and 20 for Great Black-backed Gull. The Severn Estuary, largely due to the roost at Frampton & Waveridge Sands, held an estimated 7% of the minimum population estimate of Black-headed Gulls, 8% of Common Gulls and 29% of Lesser Black-backed Gulls.

7. Only inland sites in England (and the large roost at Frampton & Waveridge Sands on the Severn Estuary) were looked at in every one of the five surveys. All species increased in number here between the first survey in 1953 and that in 1993, though rates of change varied between species. The numbers of Black-headed Gulls counted increased by 244%, those of Common Gulls by 472%, those of Great Black-backed Gull by 732% and those of Lesser Black-backed Gull by 16,402%. The numbers of Herring Gull counted increased overall by 81% between 1953 and 1993, though declined greatly between 1973 and 1983. The increases in gull populations have probably resulted in increases in both the number of roost sites occupied and the numbers of gulls using individual roosts.

8. Analysis of data from three in-depth studies suggested that single counts, such as those used by the Winter Gull Roost Surveys, may not be representative of numbers over the winter as a whole. Thus, whilst single co-ordinated counts may provide estimates of the national populations present at a fixed time during winter, it may be important to monitor key sites over several months if total site usage is to be estimated.

9. Improvements to the existing methodology are recommended for future surveys, so as to provide more accurate estimates (with confidence limits) of the UK’s wintering gull populations. Such surveys should aim to provide separate estimates of gull populations inland and on the coast, by extrapolating from the samples of sites counted.

10. The suggested date for the next Winter Gull Roost Survey is the winter of 2003/04. Pilot work suggested for the winter of 2002/03 would aim to test methods of counting gulls flying in to roost along defined stretches of coast and include a study of the timing of arrival of gulls at roosts.

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