The formation of foraging aggregations in a highly social seabird, the thick-billed murre (Uria lomvia), at small and large scales
Analyzing how animals are distributed in space and time is important to understand the behavioural interactions that underlie population dynamics, especially for highly social species. Thick-billed murres (Uria lomvia) breed in some of the largest and densest colonies of any seabird. Although this bird is known to aggregate at sea, little is known about when, where, and why the birds form aggregations. We examined the spatial and temporal patterns of foraging aggregations during the breeding season through various scales via (1) measurement of the synchrony of arrivals of adults feeding their chicks at the colony, and (2) use of both GPS and camera loggers attached on the birds to examine the proximity of birds at sea. Adult arrivals at the colony were synchronised when bringing capelin (Mallotus villosus), a gregarious pelagic fish, but not when bringing sculpin (primarily Triglops spp.), a solitary benthic fish. Camera loggers revealed very close encounters of foraging conspecific (< 4 m), much closer than what was predicted by chance, despite low prey densities. GPS loggers also showed diffuse at-sea aggregations with minimal distances closer than expected by chance. However, those study birds did not typically share foraging trajectories. We suggest that, at smaller scales, murres form tight groups to increase searching efficiency underwater. At larger scales, murre aggregations are most likely a result of foraging individuals converging in the more prolific areas, either by independently encountering prey hotspots, or by cueing on other foraging birds.
We thank S. Flemming, E. Gongora, A. Patterson, S. Poole, F. St. Aubin, and all other field assistants who took part of the data collection at Coats, as well as J. Nakoolak for keeping us safe from bears. We thank Tony Gaston for revising the manuscript and sharing with us his extensive knowledge on murres. We would also like to thank the Northern Scientific Training Program, Canada Research Chair in Arctic Ecology, Environment and Climate Change Canada, Polar Continental Shelf Project, and the Arctic Institute of North American for funding. R. Amstrong at the Nunavut Research Institute and M. Janssen at Environment Canada helped with logistics. Finally, we thank A. Patterson for revising the early drafts of the manuscript, and K. Lalla, F. Rakic, E. Ste Marie, and F. Van Oordt for help with GPS analyses.
Compliance with ethical standards
Conflict of interest
There is no conflict of interest for any of the authors. All applicable Canadian guidelines for the care and use of animals were followed.
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