Andrew J. Musgrove

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

Abstract Great Britains 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 Britains coasts than the traditional approach based on averaging just January counts over a 5-year period, and it suggests that Great Britains 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.

Birds of the Severn Estuary and Bristol Channel: Their current status and key environmental issues

The Severn Estuary and Bristol Channel encompass a number of designated sites supporting populations of waterbirds and seabirds that are of national or international importance, including the Severn Estuary and Burry Inlet Special Protection Areas (SPAs)/Ramsar Sites and Carmarthen Bay, the UKs first marine SPA. Here, we provide an overview of the present numbers and trends of the waterbirds and seabirds using these sites, updating previous reviews undertaken prior to these designations. We further provide a summary of the main issues that have affected the status of the areas bird populations. Declines in the numbers of waders on the Severn Estuary and the southwest over the last two decades have been linked to climate change. The Sea Empress oil-spill impacted both breeding seabirds and the wintering Common Scoters in Carmarthen Bay, though numbers of the latter recovered 3years after the spill. At the Burry Inlet, Oystercatcher numbers have fallen over the last 25years and considerable research has been undertaken into the conflict with cockle and mussel fisheries. A long-term study at Cardiff Bay, at the mouth of the Severn, revealed a significant impact on the survival of Redshanks following its impoundment and has helped to further understanding of responses of waterbirds to estuarine habitat loss. The potential impacts of the construction of a tidal power scheme on the Severn Estuary are also discussed.

The Sea Empress oil spill (Wales, UK): Effects on Common Scoter Melanitta nigra in Carmarthen Bay and status ten years later

Carmarthen Bay, UK, regularly supports internationally important numbers (>16,000) of non-breeding Common Scoters Melanitta nigra. The spill of 72,000 tonnes of crude oil from the Sea Empress in 1996 affected birds both through direct mortality and likely pollution of key food resources. Numbers were greatly reduced following the spill, whilst changes in the distribution of birds within Carmarthen Bay suggested that potentially sub-optimal foraging zones were used. However, ten years after the incident, numbers of Common Scoter were no different to those recorded immediately before the spill. Compared to some other spills, rapid revival is evident. Numbers increased to pre-spill levels within three winters and distributional changes suggested a concurrent return to previously contaminated feeding areas, implying that the ecosystem had regenerated sufficiently to support its top predator. The importance of prolonged, standardised monitoring of bird numbers and distribution as indicators of ecological recovery from environmental damage is emphasised.