Conspecific nest attendance behaviour of Common Eider (<i>Somateria mollissima</i>) in response to Polar Bear (<i>Ursus maritimus</i>) foraging activity: error or intent?

Abstract

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.

An interspecific foraging association with polar bears increases foraging opportunities for avian predators in a declining Arctic seabird colony

“…When an eider flushed, we recorded the number of gulls observed in the paused video frame. Following each eider's flush, we recorded if the bear or any gulls visited the nest and whether either predator consumed eider nest contents (hereafter referred to as “eggs,” although ducklings may have been present at this time, see Simone et al., 2022 ). We defined nest visits for bears and gulls as behaviours where the predator approached the focal nest and appeared to touch the eider nest bowl or contents.…”

“…Climate‐induced reductions in spring sea ice are forcing bears ashore earlier in the year in many populations (Derocher et al., 2004 ; Lunn et al., 2016 ; Regehr et al., 2007 ), which has led to increased foraging on several nesting bird species (Barnas, Darby, et al., 2022 ; Barnas, Iles, et al., 2020 ; Iverson et al., 2014 ; Jagielski, Dey, Gilchrist, Richardson, Love, & Semeniuk, 2021 ; Jagielski, Dey, Gilchrist, Richardson, & Semeniuk, 2021 ; Prop et al., 2013 ; Rockwell & Gormezano, 2009 ; Smith et al., 2010 ). As bears move through nesting bird colonies, incubating parents can be disturbed off their nests (Barnas, Geldart, et al., 2022 ; Gaston & Elliott, 2013 ; Jagielski, Dey, Gilchrist, Richardson, Love, & Semeniuk, 2021 ; Simone et al., 2022 ), but see Barnas, Darby, et al. ( 2022 ), leading to an increase in unguarded eggs that are more easily accessible to avian predators (Harvey, 1971 ; Inglis, 1977 ; Prop et al., 1985 ).…”

“…While foraging avian predators are more mobile than incubating parents or seasonally flightless adults, there remains a predation risk by bears to these follower species (Stempniewicz, 2006 ). Behaviours of incubating parent birds can also influence predation risk, as increased parental activity at nests may serve as visual cues for both avian predators and bears (Barnas, Geldart, et al., 2022 ; Simone et al., 2022 ).…”

“…Climate-induced reductions in spring sea ice are forcing bears ashore earlier in the year in many populations (Derocher et al, 2004;Lunn et al, 2016;Regehr et al, 2007), which has led to increased foraging on several nesting bird species (Barnas, Darby, et al, 2022;Barnas, Iles, et al, 2020;Iverson et al, 2014;Jagielski, Dey, Gilchrist, Richardson, Love, & Semeniuk, 2021;Prop et al, 2013;Rockwell & Gormezano, 2009;Smith et al, 2010). As bears move through nesting bird colonies, incubating parents can be disturbed off their nests (Barnas, Geldart, et al, 2022;Gaston & Elliott, 2013;Jagielski, Dey, Gilchrist, Richardson, Love, & Semeniuk, 2021;Simone et al, 2022), but see Barnas, Darby, et al (2022), leading to an increase in unguarded eggs that are more easily accessible to avian predators (Harvey, 1971;Inglis, 1977;Prop et al, 1985). Disturbance foraging by avian predators is well documented during researcher activities in Arctic bird colonies (Åhlund & Götmark, 1989;Bêty & Gauthier, 2001;Götmark, 1992;Götmark & Åhlund, 1984), and increased bear presence in Arctic bird colonies will likely lead to greater disturbances, thus creating more foraging opportunities for avian predators.…”

Heightened heart rate but similar flight responses to evolved versus recent predators in an Arctic seabird

“…Additionally, an early escape may allow eiders time to cover their nests with insulating down before leaving the nest to protect their clutch from secondary predators and adverse weather conditions (Mehlum 1991). Alternatively, it may also be adaptive for eiders to rely on crypsis and flush at a short distance only when they have been detected by bears if eider distraction displays are an effective strategy to draw bears' attention away from their nest (i.e., active deception, Kay and Gilchrist 1998;Barnas et al 2022;Simone et al 2022).…”