Andy Webb

Changes in body mass of Common Guillemots Uria aalge in southeast Scotland throughout the year: Implications for the release of cleaned birds

Body masses of Common Guillemots Uria aalge in southeast Scotland showed a pronounced annual cycle with birds being consistently heavier during the moult and over the winter. On average, adults were significantly heavier than immatures and males tended to be heavier than females. Masses of both breeding adults and immature birds declined during the breeding season. Comparisons of the body masses of wild birds and those released from rescue centres after treatment and cleaning, indicated that the latter were about 30% lighter, a difference which might explain why the survival prospects of such birds are currently so poor. The problems associated with setting target release masses for Guillemots are discussed.

Revised estimate of numbers of wintering Red-throated Divers Gavia stellata in Great Britain

Capsule An estimated 17 000 Red-throated Divers winter around Great Britain. Aim To produce an up-to-date assessment of the numbers of Red-throated Divers wintering around Great Britain. Methods A revised Great Britain (GB) wintering population estimate for Red-throated Divers was compiled using data primarily from systematic line transect surveys by aircraft over marine nearshore areas conducted during 2001–06, supplemented with county bird records and Wetland Bird Survey (WeBS) counts, both from 1995 to 2005. Population estimates for each survey area around GB were calculated as the mean of either annual means (aerial surveys) or annual maxima (WeBS, county bird records) of all data collected within January and February of each year. These were summed to give a revised GB wintering population estimate. Results A total of 17116 (13198–21034, 95% confidence interval) Red-throated Divers were estimated to winter around GB. Distribution was uneven. By far the greatest numbers were found off southeast and east Britain (59.3% of the total was between Flamborough Head, Yorkshire, and Dungeness, Kent), with large concentrations off the English south coast (10.9%), north Wales and Liverpool Bay (9.8%), and eastern Scotland (6.1%). Conclusion This is a minimum plausible population estimate and the true population size may be larger. The new 1% of population threshold for statutory conservation work is 170 birds.

The distribution of auks and Procellariiformes in north-west European waters in relation to depth of sea

The distribution of 5 species of auks and 3 species of Procellariiformes in northwest European waters was analysed in relation to 5 depth zones. Auks and Manx Shearwaters were restricted mainly to the continental shelf. Fulmars and British Storm Petrels were found mostly in waters of greater than 100 m depth. Interspecific variation in distribution may be related to dietary differences. The presence of fishing vessels was considered to be of secondary importance for Fulmars.

The distribution of Manx Shearwaters Puffinus puffinus in north-west European waters

Seabirds in north-west European waters were surveyed offshore throughout the year from 1979 to 1993. During the breeding season the distribution of Manx Shearwaters centred around the main colonies of Rhum, Skomer and Skokholm. Densities were low in the North Sea, where birds were mainly restricted to waters off the north-east coasts of England and Scotland, in particular the Moray Firth, the Firth of Forth and Flamborough Head. Manx Shearwaters can forage at long distances from the colonies, but highest densities were observed in the Irish Sea, south-west Wales, south-west Ireland and the inshore waters of West Scotland during the chick-rearing period when parent birds visit the colony more frequently. The area of the Irish Sea front was important, particularly in the autumn, and feeding occurred here in preference to other areas of the Irish Sea. From November to February Manx Shearwaters were virtually absent from north-west European waters.