A revision of population estimates for waders (Charadrii) wintering on the coastline of Britain

Abstract

Abstract Recent surveys have revealed that approximately 1·3 million waders winter on the British coastline. Dunlin Calidris alpina , oystercatcher Haematopus ostralegus and knot Calidris canutus were the most abundant species, together making up two-thirds of the total. More than 80% of the waders were found on estuaries, although these habitats comprise less than one-quarter of the coastline, by length; furthermore, more than 50% of the waders occured, in mid-winter, on only ten estuaries. The patterns of dispersion varied between species. The estuaries supported all or most of the national populations of black-tailed godwit L. limosa , knot, dunlin, bar-tailed godwit Limosa lapponica and grey plover Pluvialis squatarola , whilst purple sandpiper Calidris maritima , turnstone Arenaria interpres , ringed plover Charadrius hiaticula and sanderling Calidris alba were typically non-estuarine shore species. The winter populations of black-tailed godwit, bartailed godwit, knot, oystercatcher and dunlin are concentrated into a few estuaries, while the other species are more dispersed. The implications of these patterns are discussed with respect to estuarine habitat loss. The revised population estimates were similar to those from earlier studies for five species, were lower for two species, and were higher for five species. New values are recommended for use in ornithological site assessments, based on the criterion of 1% of the national population. The delimitation of sites, for such evaluations, is discussed.