4. Discussion
Counts of nesting eiders in 103 study colonies around the Baltic Sea between 2007 and 2010 showed that colonies situated in the central and southern Baltic Proper declined very sharply in size from 2007 to 2008. The declines were followed by increases in the same colonies in 2009 and 2010, although not always up to the level observed in 2007. By contrast, in the study colonies situated in the northeastern Baltic Sea and in the Gulf of Finland no general decline of the number of nesting eiders were observed between 2007 and 2008.