Population estimates for waders Charadrii wintering in Great Britain, 1987/88–1991/92

Abstract

Britain's wintering wader populations were estimated for the period 1987/88–1991/92 from data provided from three sources: the Wetland Bird Survey (WeBS), the Winter Shorebird Count and the Winter Atlas. WeBS is the annual monitoring scheme for non-breeding waterfowl populations in the United Kingdom. It achieves excellent coverage of the important concentrations of waders living within estuaries, but the coverage of populations using non-estuarine coasts and inland habitats is incomplete. The Winter Shorebird Count, conducted in 1984/85, was a comprehensive survey of waders wintering on non-estuarine coasts while the Winter Atlas provides distributional data for all bird species in Britain and Ireland for three winters in the early 1980s and is a source of information on inland wader populations. The wader populations on non-estuarine coasts were estimated from sites counted in both 1984/85 and in 1987/88–1991/92 as part of WeBS, enabling calibration of the Winter Shorebird Count data. The results suggest that Britain's coastline supports approximately 1·65 million waders. Values are presented from which site evaluations based on 1% of the national population can be derived. Comparison of the new coastal population estimates with the previous estimates (for the period 1981–1985) suggests that numbers of most species of wintering waders have increased on estuaries and non-estuarine coasts during the last decade. These population changes are compared with trends in British wintering wader populations as shown by application of a model-based method of indexing populations. The possible causes of between-year fluctuations in wader populations are discussed and the importance of long-term monitoring schemes emphasised.