Recent changes in breeding abundance and distribution of the Common Pochard(Aythya ferina)in its eastern range

摘要

Background:The Common Pochard(Aythya ferina)(hereafter Pochard),a widespread and common freshwater diving duck in the Palearctic,was reclassified in 2015 from Least Concern to Vulnerable IUCN status based on rapid declines throughout its range.Analysis of its status,distribution and the potential causes for the decline in Europe has been undertaken,but there has never been a review of its status in the major part of its breeding range across Russia to the Pacific coast.Methods:We reviewed the scientific literature and unpublished reports,and canvassed expert opinion throughout Russia to assess available knowledge about changes in the species distribution and abundance since the 1980s.Results:While accepting available information may not be representative throughout the entire eastern range of the species,the review found marked declines in Pochard breeding abundance in the last two decades throughout European Russia.Pochard have also declined throughout Siberia.Declines throughout the steppe region seemed related to local drought severity in recent years,necessitating further research to confirm this climate link at larger spatial scales.Declines in the forest and forest-steppe regions appeared related to the major abandonment of fish farms in western Russia that had formerly provided habitat for breeding Pochard.However,hyper-eutrophication of shallow eutrophic lakes,cessation of grazing and haymaking in floodplain systems necessary to maintain suitable nesting habitat and disappearance of colonies of the Black-headed Gull(Chroicocephalus ridibundus)in a number of wetlands were also implicated.Increasing invasive alien predator species(e.g.American Mink Neovison vison and Raccoon Dog Nyctereutes procyonoides)and increasing spring hunting were also thought to contribute to declines.Reports of expansion in numbers and range only came from small numbers occurring in the Russian Far East,including on the border with China and the long-established isolated population on Kamchatka Peninsula.Conclusions:Widespread declines throughout the eastern breeding range of the Pochard give continued cause for concern.Although we could address all the potential causal factors identified above by management interventions,we urgently need better information relating to key factors affecting site-specific Pochard breeding success and abundance,to be able to implement effective actions to restore the species to more favourable conservation status throughout its breeding range.