Declines have also been found around British coasts, with long-tailed duck, velvet scoter and red-breasted merganser among those hardest hit. In North America the trend continues with several seaduck populations significantly down, among them black scoters, white-winged scoters and surf scoters.
âThese birds just seem to have gone missing,â said Richard Hearn, Head of Species Monitoring at the Wildfowl & Wetlands Trust and Chair of the IUCN-SSC/Wetlands International Duck Specialist Group.
âThe scale of the declines in Europe is very surprising and largely unexpected. Most of these species remain relatively numerous but if their numbers continue to fall at these rates, some of these species could soon be in serious trouble.â
A report published today, Waterbird Populations and Pressures in the Baltic Sea, shows that the number of waterbirds wintering in the Baltic fell overall by 40%, from 7.44 million to 4.41 million. The declines were revealed by two censuses, staged from 1992-3 and 2007-9.
Concerns have been reinforced by monitoring elsewhere showing much smaller numbers of seaducks in important British sites such as the Moray Firth and Clyde Estuary, and in the Netherlands.
Seaducks and other birds migrate in autumn to escape deteriorating conditions at their high Arctic breeding grounds. Some head for the Baltic while others continue west. But if winters are mild they may not fly so far, swelling numbers in continental Europe but reducing populations in the UK.
Until recently, conservationists had largely attributed falling UK numbers to this âshort-stoppingâ but now they fear the situation for some species is more serious.
Several causes could be to blame. âIt could be oil pollution, reduced food in the Baltic Sea, or something happening in the birdsâ Arctic breeding grounds,â Richard Hearn said.
Climate change could be disrupting the natural balance between predators and prey, scientists fear. If there are fewer lemmings for example, arctic foxes, skuas and snowy owls are forced to seek other sources of food.
âBirds also die in fishing nets but itâs unlikely that the nets would kill so many. Shipping, development and over-fishing are all increasing, however, which could be significant. It may be that a few factors are acting together to cause these massive declines.â
Richard Hearn is urging European seaduck experts to meet in the spring to draw up an action plan to tackle the problem.
He hopes that measures will win backing from EU policy makers, particularly since the global red list status of some seaduck species may soon be raised by the IUCN.