The role of the male common eider Somateria mollissima as a protector against nest-predation

Abstract

Male common eiders Somateria mollissima in high-Arctic colonies are known to remain with females during the first weeks of incubation; a behaviour not found in eider colonies further south. Other studies have observed that, whilst adult eiders in northern latitudes experience less predation, there can be much higher levels of predation on their nests and young. The objective of this study was to investigate why males at an eider colony in Svalbard were present for longer than elsewhere in their range, and whether this was related to protection from high predation levels. Through an observational study design, this study mapped population and predator dynamics within an eider colony near Longyearbyen, Svalbard. This study found that males were present for several weeks after the first females had started incubating, and once most males left the colony there was an increase in predation. Success of predators was higher at unattended nests; however overall success of predators was not found to be significantly lower if males were present in addition to females. If males were present at the nest, females were less likely to leave their nest to respond to gulls, allowing females to conserve energy and leave nests covered. The possibility that the tendency of males to remain with females for longer has emerged from asynchronous breeding or extra-pair mating is discussed, but the findings from this study indicate that it is a direct response to high levels of predation.