Exploring the energetic consequences and decision-making behaviours of polar bears (Ursus maritimus) foraging on common eider (Somateria mollissima) seaduck eggs on Mitivik Island, Nunavut

Climate change is projected to further degrade sea-ice conditions in the Arctic, causing disruptions in the foraging ecology of animals. Polar bears (Ursus maritimus) will likely continue to suffer declines in fitness if they are unable to supplement lost on-ice hunting opportunities with terrestrial resources. My thesis aimed to investigate whether polar bears accrue a net energetic gain from foraging on common eider (Somateria mollissima) eggs and whether the decisions they make when foraging on eggs are consistent with optimal foraging theory. Using aerial footage of bears foraging on common eider eggs, I estimated the energetic consequences of foraging on eggs, and examined polar bears’ foraging performance as the resource was depleted. My results indicate that polar bears consumed eggs at a decelerating rate. While the proportion of time spent searching in the colony increased as the season advanced, the energetic cost of searching remained constant throughout the season as a result of similar costs of expenditure across locomotion and feeding. Overall, while some bears gain an energetic surplus from egg foraging, the benefits decline with nest density, resulting in a net loss. Further, my results indicate that as the resource depleted, polar bears did not adjust all their foraging decisions to match resource density. Bears increased their visitation rates to nests that were ‘empty’, despite visiting fewer nests overall. Polar bears did not adjust their movement to nest density, but did become less selective in their choice of which clutches of eggs to consume. Lastly, bears that capitalized on the visual cue of a flushing eider hen to locate nests also significantly increased the number of clutches they consumed.