It is well known that individual colonies, or groups of eider colonies within a region, can be greatly affected or eradicated, for example, by fox predation or by outbreaks of avian cholera or other diseases during the nesting stage (Christensen et al., 1997 and Pedersen et al., 2003). However, none of the 28 study island in the southern and central Baltic Sea showed any signs of fox predation during the four year study period. We neither found indications of any outbreak of avian cholera or other acute diseases.