Going deep: common murres dive into frigid water for aggregated, persistent and slow-moving capelin
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ORIGINAL PAPER
Going deep: common murres dive into frigid water for aggregated, persistent and slow-moving capelin April Hedd Æ P. M. Regular Æ W. A. Montevecchi Æ A. D. Buren Æ C. M. Burke Æ D. A. Fifield
Received: 17 July 2008 / Accepted: 20 December 2008 / Published online: 31 January 2009 Ó Springer-Verlag 2009
Abstract Owing to the necessity of delivering food to offspring at colonies, breeding seabirds are highly constrained in their foraging options. To minimize constraints imposed by central-place foraging and to optimize foraging behavior, many species exhibit flexible foraging tactics. Here we document the behavioral flexibility of pursuitdiving common murres Uria aalge when foraging on female capelin Mallotus villosus in the northwest Atlantic. Quite unexpectedly, being visual foragers, we found that common murres dived throughout the day and night. Twenty-one percent of recorded dives (n = 272 of 1,308 dives) were deep (C50 m; maximum depth = 152 m, maximum duration = 212 s), bringing murres into sub-0°C water in the Cold Intermediate Layer (CIL; 40–180 m) of the Labrador Current. Deep dives occurred almost exclusively during the day when murres would have encountered spatially predictable aggregations of capelin between 100 and 150 m in the water column. Temperatures within the CIL shaped trophic interactions and involved trade-offs for both predators and prey. Sub-0°C temperatures limit a fish’s ability to escape from endothermic predators by reducing burst/escape speeds and also lengthening the time needed to recover from burst-type activity. Thus, while deep diving may be energetically costly, it likely increases certainty of prey capture. Decreased murre foraging efficiency at night (indicated by an increase in the number of
Communicated by R. Lewison. A. Hedd (&) P. M. Regular W. A. Montevecchi A. D. Buren C. M. Burke D. A. Fifield Cognitive and Behavioural Ecology Program, Psychology Department, Memorial University, St John’s, NF A1B 3X9, Canada e-mail: [email protected]
dives per bout) reflects both lower light conditions and changing prey behavior, as capelin migrate to warmer surface waters at night where their potential to escape from avian predators could increase.
Introduction Biophysical variability in dynamic marine environments affects the performance, behavioral ecology and distribution of both predators and prey (Domenici et al. 2007). During breeding, the demands of central-place foraging greatly restrict the foraging options and provisioning opportunities of seabirds (Orians and Pearson 1979), often challenging their behavioral and physiological capabilities (Weimerskirch et al. 2003; Jodice et al. 2006; Elliott et al. 2008a). Seabirds may consequently employ flexible foraging tactics in an effort to minimize constraints and effectively cope with breeding demands. Seabird species that fly and dive are compromised in both forms of locomotion (Burger 1991). Pursuit-diving alcids have taken these adaptations to extremes and exhibit considerable performance capability and agilit
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