Effects of Experimental Manipulation of Incubation Length on Behavior and Body Mass of Common Eiders in the Canadian Arctic

In 1998 and 1999, the costs of experimentally extending incubation among female Common Eiders (Somateria mollissima) were examined in relation to changes in female body mass. Clutches were switched between nests to extend incubation by an average of five days to compare with control clutches. In the four days prior to hatch, females with manipulated clutches incubated less per day, and lost more body mass than control females. The probability of nest failure was similar for control and manipulated females. Manipulated females who lost their clutches to predation or abandonment appeared to have greater body mass than those who hatched their eggs successfully. Manipulated females who were unsuccessful also took more frequent incubation recesses than those who hatched eggs successfully. The probability of return to the colony in the following year did not differ significantly between control (66%) and manipulated females (57%). These results suggest that some female Common Eiders breeding in the arctic can physically increase their incubation effort and decrease their body condition at the end of the breeding season with no major consequences to long-term survival.