The Role of Failed Nesters and Brood Abandoning Females in the Creching System of the Common Eider Somateria mollissima

In Common Eiders, females other than the mother often protect young from predators. This study was designed to determine if failed nesters and females which loose their young shortly after hatching (brood abandoners) participate in such rearing activities. Brood caring females always reacted aggressively towards approaching gulls and stayed close to the young during disturbance. The behaviour of failed nesters and brood abandoners towards broods and creches was similar. Their creche attendance was highly temporal and independent of the time since they had lost their eggs or hatched their young. They usually left the creches at the slightest disturbance, and during gull attacks failed nesters showed no reaction while a few brood abandoners tending creches reacted aggressively. Most of the creche attendance in nest-failing and brood abandoning females is presumably motivated by selfish interest, e.g. seeking safety from predators or kleptoparasites. The so-called visiting females or aunts in Eider creches should be divided in two categories: broody females showing protective behaviour and females temporarily attending creches and showing no broodiness. Failed nesters and most of the brood abandoners belong to the latter category. Most of the females showing protective behaviour probably belong to the non-breeding cohort (young and/or non-breeding birds).