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Common eiders nesting in the Baltic Sea are exposed to generally high levels of contaminants including potentially genotoxic polycyclic aromatic hydrocarbons and organochlorines. Blood samples were collected from eiders at eight sites in the Baltic Sea and two sites in the Beaufort Sea. DNA content variation was estimated using the flow cytometric method, and subsequently utilized as a biomarker of genetic damage. We observed no significant differences in genetic damage among populations within either the Baltic or Beaufort Seas. However, eider populations from the Baltic Sea had significantly elevated estimates of genetic damage compared to populations from the Beaufort Sea.

The phenology of spring migration depends on the severity of the preceding winter and approaching spring. This severity can be quantified using the North Atlantic Oscillation (NAO) index; positive values indicate mild winters. Although milder winters are correlated with earlier migration in many birds in temperate regions, few studies have addressed how climate-induced variation in spring arrival relates to breeding success. In northern Europe, the NAO-index correlates with ice cover and timing of ice break-up of the Baltic Sea. Ice cover plays an important role for breeding waterfowl, since the timing of ice break-up constrains both spring arrival and onset of breeding. We studied the effects of the winter-NAO-index and timing of ice break-up on spring migration, laying date, clutch size, female body condition at hatching and fledging success of a short-distance migrant common eider ( Somateria mollissima) population from SW Finland, the Baltic Sea, 1991–2004 (migration data 1979–2004). We also examined the correlation between the NAO-index and the proportion of juvenile eiders in the Danish hunting bag, which reflects the breeding success on a larger spatial scale. The body condition of breeding females and proportion of juveniles in the hunting bag showed significant positive correlations with the NAO, whereas arrival dates showed positive correlations and clutch size and fledging success showed negative correlations with the timing of ice break-up. The results suggest that climate, which also affects ice conditions, has an important effect on the fledging success of eiders. Outbreaks of duckling disease epidemics may be the primary mechanism underlying this effect. Eider females are in poorer condition after severe winters and cannot allocate as much resources to breeding, which may impair the immune defense of ducklings. Global climate warming is expected to increase the future breeding success of eiders in our study population. [ABSTRACT FROM AUTHOR]