Numbers of wintering waterbirds in Great Britain and the Isle of Man (1994/1995-1998/1999): II. Coastal waders (Charadrii)

Great Britain's wintering coastal wader populations have been estimated for the period 1994/1995-1998/1999 from data provided from two sources: the Wetland Bird Survey (WeBS) and the Non-estuarine Coastal Waterfowl Survey (UK-NEWS). New methodology for estimating the number of wintering waders is applied. It imputes (fills in) the value of missing counts before estimating the population size of each species as being the mean of the largest annual count made between November and March over the relevant 5-year period. This methodology has led to an 11% larger estimate of the number of waders present on Great Britain's coasts than the traditional approach based on averaging just January counts over a 5-year period, and it suggests that Great Britain's coastline supports ca. 2.1 million waders. Updated values are presented from which site evaluations based on 1% of the national population can be derived. Great Britain is of considerable international importance for waders. It holds >25 and >50% of the flyway populations of nine and four species of wader, respectively, but for the first time since the start of monitoring in the early 1970s, the historical increase in the number of predominantly coastal waders wintering in Great Britain is coming to an end. Seven of the 14 species that have shown population changes of >5% since the last set of 1987/1988-1991/1992 population estimates have declined in numbers. The possible causes of the fluctuations in wader populations, such as climate change and changing nutrient inputs to coastal waters are discussed. There is an urgent need to identify the causative factors leading to these declines, and to use the new population estimates to identify new sites that should be afforded legal protection, an action that should help Great Britain maintain its internationally important wader populations. The decrease in the updated population estimate of Eurasian oystercatcher, for example, has made it possible to determine that 19 rather than 17 sites in Great Britain are worthy of statutory protection on the basis of holding 1% or more of its national population.