Common Eider (Somateria mollissima) is a colonial nesting sea duck with extremely high nest attendance rates. Although individuals take few recess breaks away from their nest to feed or preen, previous research has shown that some female eiders in dense nesting assemblages engage in conspecific nest attendance, spending short amounts of time incubating nests of other females. However, to the best of our knowledge, most observations of these behaviours occur during regular recess events, as opposed to instances where females flush from their nest in response to a foraging predator. Using drone videography on East Bay Island, northern Hudson Bay, Nunavut, Canada, we observed conspecific nest attendance behaviours in 11 eiders that flushed in response to a foraging Polar Bear (Ursus maritimus). Of the 11 birds attending to other nests, only two predation events were observed at the focal bird’s nest (i.e., two attenders’ own nests were predated). Of the nine nests that were attended to, we also only observed two predation events. Motivations behind these behaviours are unclear, but conspecific nest attendance may serve as a type of distraction display, whereby activity at another female’s nest leads the predator away from the focal bird’s nest. However, given that, on East Bay Island, eiders are known to nest in proximity to kin, distraction displays at nests of related individuals would incur fitness costs. General confusion on nest location or the concealment of closely related eggs are more likely explanations for these behaviours.

Predator-prey dynamics in the Arctic are being altered with changing sea ice phenology. The increasing frequency of predation on colonial nesting seabirds and their eggs by the polar bear (Ursus maritimus) is a consequence of bears shifting to terrestrial food resources through a shortened seal-hunting season. We examined antipredator responses in a colony of nesting Common Eiders (Somateria mollissima) on East Bay Island, Nunavut, Canada, which is exposed to established nest predators, such as arctic fox (Vulpes lagopus), but also to recent increases in polar bear nest predation due to the bears' lost on-ice hunting opportunities. Given eiders' limited eco-evolutionary experience with bears, we aimed to experimentally contrast eider responses to the recent predation pressure by polar bears to those induced by their more traditional mammalian predator, the arctic fox. Our goal was to characterize whether this population of eiders was vulnerable to a changing predator regime. Using simulated approaches of visual stimuli of both predator types, we measured eider heart rate and flight initiation distance as physiological and behavioral metrics, respectively, to characterize the perceived risk of and subsequent response to imminent threat posed by these two predators that differ in historical encounter rates. Eider heart rates were more responsive to impending visual cues of arctic foxes compared to polar bears, but birds responded behaviorally to all simulated threats with similar flight initiation distances. Results suggest eiders may not perceive the full risk that bears pose as egg and adult predators, and are therefore expected to suffer negative fitness consequences from this ongoing and increasing interaction. Eiders may therefore require conservation intervention to aid in their management. Rythme cardiaque plus élevé mais réaction de vol similaire face aux prédateurs évolués par rapport aux prédateurs récents chez un oiseau marin de l'ArctiqueRÉSUMÉ. Dans l'Arctique, la dynamique prédateur-proie change en raison des modifications qui adviennent dans la phénologie des glaces de mer. La fréquence accrue de la prédation par l'ours blanc (Ursus maritimus) d'oiseaux marins nichant en colonie et de leurs oeufs découle du fait que les ours se tournent vers les ressources alimentaires terrestres en raison de la saison de chasse aux phoques plus courte. Nous avons examiné les réactions anti-prédation d'Eiders à duvet (Somateria mollissima) nichant en colonie sur l'île d'East Bay, au Nunavut, Canada, qui sont exposés à des prédateurs de nids établis, tels que le renard arctique (Vulpes lagopus), mais aussi à une hausse récente de la prédation de nids par l'ours blanc en raison de la perte d'occasions de chasse sur la glace pour l'ours. Compte tenu de l'expérience éco-évolutive limitée des eiders avec les ours, nous avons cherché à contraster de façon expérimentale les réactions des eiders à la pression de prédation récente par les ours blancs avec celle induite par leur prédateur mammifère plus traditionnel, le renard...