An interspecific foraging association with polar bears increases foraging opportunities for avian predators in a declining Arctic seabird colony
Date
2024
Authors
Barnas, Andrew
Simone, Cassandra
Geldart, Erica
Love, Oliver
Jagielski, Patrick
Gilchrist, H. Grant
Richardson, Evan
Dey, Cody
Semeniuk, Christina
Journal Title
Journal ISSN
Volume Title
Publisher
Ecology and Evolution
Abstract
Interspecific foraging associations (IFAs) are biological interactions where two or more species forage in association with each other. Climate-induced reductions in Arctic sea ice have increased polar bear (Ursus maritimus) foraging in seabird colonies, which creates foraging opportunities for avian predators. We used drone video of bears foraging within a common eider (Somateria mollissima) colony on East Bay Island (Nunavut, Canada) in 2017 to investigate herring gull (Larus argentatus) foraging in association with bears. We recorded nest visitation by gulls following n = 193 eider flushing events from nests during incubation. The probability of gulls visiting eider nests increased with higher number of gulls present (β = 0.14 ± 0.03 [SE], p < .001) and for nests previously visited by a bear (β = 1.14 ± 0.49 [SE], p < .02). In our model examining the probability of gulls consuming eggs from nests, we failed to detect statistically significant effects for the number of gulls present (β = 0.09 ± 0.05 [SE], p < .07) or for nests previously visited by a bear (β = −0.92 ± 0.71 [SE], p < .19). Gulls preferred to visit nests behind bears (χ2 = 18, df = 1, p < .0001), indicating gulls are risk averse in the presence of polar bears. Our study provides novel insights on an Arctic IFA, and we present evidence that gulls capitalize on nests made available due to disturbance associated with foraging bears, as eiders disturbed off their nest allow gulls easier access to eggs. We suggest the IFA between gulls and polar bears is parasitic, as gulls are consuming terrestrial resources which would have eventually been consumed by bears. This finding has implications for estimating the energetic contribution of bird eggs to polar bear summer diets in that the total number of available clutches to consume may be reduced due to avian predators.
Description
Keywords
animal behaviour, drone, eider, foraging ecology, parasitism, species interaction
Citation
Barnas, A. F., Simone, C. A. B., Geldart, E. A., Love, O. P., Jagielski, P. M., Gilchrist, H. G., Richardson, E. S., Dey, C. J., & Semeniuk, C. A. D. (2024). An interspecific foraging association with polar bears increases foraging opportunities for avian predators in a declining Arctic seabird colony. Ecology and Evolution, 14(3). https://doi.org/10.1002/ece3.11012