PARENTAL CARE IN THE COMMON EIDER (SOMATERIA-MOLLISSIMA) - FACTORS AFFECTING ABANDONMENT AND ADOPTION OF YOUNG

Parental care in common eiders (Somateria mollissima) was studied during three field seasons in northern Norway. Forty-two percent of the females were found to abandon their brood. Abandonment and tending of broods and creches were not obligate individual strategies, but changed between years. Females abandoning their young laid smaller clutches and had a lower body weight at hatching than brood- and creche-tending females, indicating that they were in poor body condition. This supports the hypothesis that abandoning the brood is a salvage strategy in which energetic stress limits females' ability to care for their young. Young of "abandoners" seemed to have a lower survival rate than young of "tenders," which suggests a reproductive cost of abandoning the young. Forty-seven percent of tagged ducklings were found with females other than their mother. Twenty-seven percent of the brood- and creche-tending females lost young to other females, but never more than one duckling. Adoptions of foreign ducklings, above the normal brood size of four, did not lead to greater parental effort, and duckling survival was similar among broods and creches of different sizes. This suggests that adoptions may be of neutral adaptive value. Two females often formed stable creches, but duckling survival was not significantly different from that in broods and creches with single females.