Migration dynamics: testing ecological theory with tracking data for Aethia Auklets in the North Pacific

Schacter, Carley (2017) Migration dynamics: testing ecological theory with tracking data for Aethia Auklets in the North Pacific. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Tracking technology has profoundly changed the study of spatial dynamics in marine vertebrates, enabling a large-scale focal-animal approach. This thesis shows that tracking data can be used, not only to characterize the annual migration cycle, but also to address ecological theory. I used geolocation tags (1g, 0.8-1.8% body mass) to investigate migration in a group of closely related seabirds. I found little evidence of negative effects of tags on Parakeet Auklets (Aethia psittacula), but tagged Whiskered Auklets (A. pygmaea) showed decreased chick growth, and reduced adult return rate. I combined tracking data with nest monitoring to test Ashmole’s hypothesis that seabird populations are regulated by decreases in local food availability during the breeding season. If food was limiting, individuals should leave soon after breeding is completed. I found no evidence to support resource depletion in planktivorous auklets. Whiskered Auklets remained near the colony all year, and lag times for Parakeet and Crested (A. cristatella) auklets were up to 30 days. Interspecific differences were more consistent with differences in migration strategy than food availability. I also synthesized several aspects of migratory theory into a migratory continuum on which I placed my three species (using a priori knowledge about distribution, and behaviour) to develop and test predictions about migration distance, consistency, and winter habitat. Tracking data supported my classification of Whiskered (residents), Parakeet (intermediate migrants) and Crested auklets (long distance directed migrants). Crested Auklets had longer migration distances than Parakeet Auklets, and greater consistency in most measures of winter habitat use. Whiskered Auklet residence is likely enabled by their less seasonal food supply, and night roosting to reduce metabolic costs. Crested Auklets’ foraging style makes them more dependent on patchy aggregations of prey, which was reflected in their concentration in highly productive areas. Parakeet Auklets spent most of the year in the deep Aleutian Basin, where their flexible diet may allow them to subsist on gelatinous zooplankton and associated amphipods. Tracking data from comparative systems like this one have great potential for addressing ecological theory, while contributing to our understanding of different ways in which seabirds have adapted to the marine environment.

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