Eider (Somateria mollissima) Science Article 6
In the present study we have made observations of eye closure duration of Common Eider Somateria mollissima in the field, to determine the amount of time devoted to sleep during the incubation period, both in breeding and non-breeding females. Breeding females started to incubate with a higher level of vigilance than non-breeding females, and increased progressively the duration of sleep over the course of incubation. At the end of the incubation period, breeding females reached a sleep time comparable to that of the non-breeding females. The data are in accordance with the hypothesis that sleep time could be modified in relation to the deterioration of body condition. Accordingly, we suggest that sleep might play a key role in saving energy when the birds experience a prolonged negative energy balance. Consequently, since female eiders can be threatened by terrestrial predators during incubation, they would therefore have to found a compromise between energy conservation while sleeping and maintenance of a threshold vigilance. Incubating female eiders could thus face conflicting priorities during incubation: that is sleeping to save energy and wakefulness for predator detection
Criscuolo F., Gauthier-Clerc M. et al., ARDEA 89 (3): 441-448.