Do activity costs determine foraging tactics for an arctic seabird?
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How energy costs affect foraging decisions is poorly understood for marine animals. To provide data relevant to this topic, we examined the relationship between activity levels and foraging behavior by attaching activity recorders to 29 chick-rearing wing-propelled diving birds (thick-billed murres, Uria lomvia) in 1999–2000. We connected the activity during the final dive bout with the prey item we observed being fed to the chicks. After accounting for changes in activity level with depth, activity was highest during the final dive of a dive bout, reflecting maneuvring during prey capture. Pelagic prey items, especially invertebrates (amphipods), were associated with higher depth-corrected activity, leading to shorter dives for a given depth (presumably due to higher oxygen consumption rates) and, thus, shorter search times (lower bottom time for a given depth). Pelagic prey items were likely captured during active pursuit, with the birds actively seeking and pursuing schooling mid-water prey. In contrast, benthic prey involved low activity and extended search times, suggesting that the birds slowly glided along the bottom in search for prey hidden in the sediments or rocks. We concluded that activity levels are important in determining the foraging tactics of marine predators.
KeywordsPrey Item Prey Type Bottom Phase Dive Depth Dive Duration
We thank R. Bull, T. Lash, D. Martin, P. Smith, U. Steiner and L. Wilson for help in the field. J. Nakoolak kept us safe from bears. K·H.E. benefited from funding provided by NSERC Postgraduate (M) Award, NSERC Northern Research Internship, Andrew Taylor Northern Studies Award, Malcolm Ramsay Award, Mountain Equipment Co-op Studentship, Arctic Institute of North America Grant-in-aid, Frank M. Chapman Memorial Fund, International Polar Year and Society of Canadian Ornithologists/Bird Studies Canada Taverner Award. K.H.E. and K.J.W. benefited from Northern Scientific Training Program of the Department of Indian Affairs and Northern Development during the field stage and funding from the 2007–2008 International Polar Year during the writing stage. The University of Pisa and Ministero della Ricerca Scientifica e Tecnologica provided funding for S.B. The Canadian Wildlife Service Migratory Birds Division, the Polar Continental Shelf Project and the University of Manitoba also funded this project. R. Armstrong at the Nunavut Research Institute and C. Eberl at the Canadian Wildlife Service in Ottawa provided logistical support. All experiments were approved under the guidelines of the Canadian Council for Animal Care.
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