| Summary: | Papers number 1, 2 and 3 of the thesis are not available in Munin due to publishers' restrictions. Papers 4 and 5 are manuscripts, and not available in Munin. 1. Jorg Welcker, Ann M. A. Harding, Nina J. Karnovsky, Harald Steen, Hallvard Strøm and Geir W. Gabrielsen: "Flexibility in the bimodal foraging strategy of a high Arctic alcid, the little auk Alle alle." Journal of Avian Biology 2009; 40(4): 388-399 (Wiley). Available at http://dx.doi.org/10.1111/j.1600-048X.2008.04620.x 2. Jorg Welcker, Harald Steen, Ann M. A. Harding and Geir W. Gabrielsen: "Sex-specific provisioning behaviour in a monomorphic seabird with a bimodal foraging strategy." Ibis 2009; 151(3): 502-513 (Wiley). Available at http://dx.doi.org/10.1111/j.1474-919X.2009.00931.x 3. Jorg Welcker, Ann M. A. Harding, Alexander S.Kitaysky, John R. Speakman and Geir W. Gabrielsen: "Daily energy expenditure increases in response to low nutritional stress in an Arctic-breeding seabird with no effect on mortality." Functional Ecology 2009; 23(6): 1081-1090 (Wiley). Available at http://dx.doi.org/10.1111/j.1365-2435.2009.01585.x 4. Jorg Welcker, Børge Moe, Claus Bech, Jannik Schultner, John R. Speakmana and Geir W. Gabrielsen: "Evidence for an energetic ceilinf in free-ranging kittiwakes (Rissa tridactyla)". Manuscript 5. Jannic Schultner, Jorg Welcker, John R. Speakman, Erling S. Nordøy and Geir W. Gabrielsen: "Application of the two-sample doubly-lebeled water method alters behavior and affects estimates of energy expenditure in black-legged kittiwakes". Manuscript Knowledge about the extent to which organisms inhabitating the Arctic are able to adjust to environmental variability is essential in order to predict the impact of future climate change. In this context, the flexibility og two Acrtic-breeding seabirds, the little Auk (Alle alle) and the kittiwake (Rissa tridactyla), in foraging behavior and energy expenditure in response to environmental variability. Analysis of the foraging behavior of little auks revealed the during chick-rearing this species adopts a bimodal foraging strategy in which they alternate single foraging trips of long duration with several trips of short length. This stereotyped pattern was found to be highly flexivle and adjusted to psatial and temporal variation in foraging conditions. However, behavioral modifications led to reduced chick feeding rates and lower reproductive success, indicating the adjustments did not allow birds to fully compensate for costs incurred by unfavorable conditions. Adjustment and limitation of energy expenditure differed remarkably between the two study species. Metabolic rate in little auks was flexible and adjusted in response to variation in food availability. Birds increased energy expenditure when food was abundant. Elevated metabolism was associated with increased chick provisioning, resulting in enhanced chick surival, and increased resource allocation to self-maintenance, associated with higher body mass and a higher return rate of individuals the subsquent season. In contrast, kittiwakes did not adjust their metabolic rate in response to environmental variability. In this species, metabolic rate was similar across five study years despite large variation in foraging conditions. Instead, kittiwakes seemed to operate close to an energetic ceiling which seemed independent of extrinsic factors. This study suggested a limited ability of Arctic seabirds to compensate for large variation to environmental conditions.
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