Since current environmental change alters the distribution, abundance and timing of prey species in marine ecosystems, higher trophic levels will need to respond to changes in food availability. Observations from seabirds in the North Atlantic and the Nor th Pacific provide evidence that trade-off decisions in responses to environmental perturbations may not be homogeneous among the regions within a single species. However, understanding why populations respond differently to these challenges will contribu te to improving our predictions on how further changes may impact populations of animals at higher trophic levels and will facilitate the design of region-specific management policies for marine areas. In this proposal, we propose to study the responses o f populations to changes in foraging conditions at the example of a long-lived seabird, the black-legged kittiwake. In a joint project of the Universities of Trondheim (Norway) and Alaska, Fairbanks (USA), and the Norwegian Polar Institute (Norway), we wi ll approach the problem by (1) studying the differences in the loss of life expectancy and in fecundity between kittiwakes from the North Atlantic and the North Pacific, by (2) assessing behavioral and metabolic responses of kittiwakes to manipulations of the physiological component of food stress, the glucocorticosteroid hormone corticosterone, and by (3) testing whether oxidative stress plays a central physiological role in mediating the trade-off decisions in kittiwakes.