Recess behaviour of the incubating Common Eider Somateria mollissima

Female eiders show the highest incubation constancy among ducks. However, detailed data on their behaviour during the short recesses were not available. In this study, activities during recesses were observed in a colony of female eiders breeding in the high arctic to define what the principal purposes of these temporary nest desertions are. Incubating eiders do not feed during their recess periods. Drinking salt or fresh water or eating snow (28.7%) and preening (38.0%) were the two main activities observed. After snow melting, the time spent drinking decreased (14.3%) while the time spent preening was unchanged (38.1%). Moreover, despite the fact that females started to fly longer distances to reach fresh water sources, the recess duration did not change significantly (401.5 vs 431.0 s). Since recess during incubation increases the risk of breeding failure, drinking presumably has an important survival value for female eiders. In this context, our data suggest that searching for fresh water at a greater distance is favoured despite the higher energetic cost for a fasting bird.