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Estimates and trends of waterbird numbers wintering in Ireland, 1994/95 to 2003/04

Abstract:

Capsule: There has been a decline in the numbers of waterbirds wintering in Ireland between 1994/95 and 2003/04, including a 5% decline in wildfowl and an 11% decline in waders. Aims: To provide estimates of numbers and trends in relative abundance of selected waterbird species wintering on the island of Ireland. Methods: Waterbird counts were undertaken at key wetland sites in Ireland each winter (September to March) between 1994/95 and 2003/04. For each species, estimates were calculated for two five-season periods (1994/95-1998/99 and 1999/2000-03/04), while trends in relative abundance were analysed over the entire ten-season period. Counts were modelled using a multiplicative log-linear index model, with site, year and month factors. Results: National estimates of overwintering numbers were produced for 42 species of waterbirds, and used to produce all-Ireland 1% thresholds (which are used to evaluate the importance of wetland sites). In winter, large proportions of several populations occur in Ireland, particularly Whooper Swan Cygnus cygnus, Greater White-fronted Goose (Greenland race) Anser albifrons flavirostris, Brent Goose (Canadian Light-bellied race) Branta bernicla hrota and Black-tailed Godwit Limosa limosa islandica. Of the 39 species for which trends were measured, 18 showed annual declines in excess of 2%, while ten species had increased. Numbers of the remaining 11 species were relatively stable. For many species, the trends measured appear to be continuations of longer-term changes since the 1970s. Conclusion: These most recent estimates of waterbird numbers have been improved compared with those previously generated, due to improved levels of coverage and better analytical methods. This study highlights that there have been significant changes in the numbers of waterbirds wintering in Ireland over the past 30 years. The fact that many of these trends parallel wider flyway-scale population trajectories implies that large-scale drivers (e.g. climate change) may be responsible. However, many of the observed declines are likely to be a consequence of increased economic development which has led to direct habitat loss to industrial and residential development. © 2008 British Trust for Ornithology.