| Summary: | Thesis (M.S.) University of Alaska Fairbanks, 2007 Recent life-history models predict that long-lived seabirds, breeding in variable food environments, should exhibit flexible reproductive effort. However, these models assume that food availability fluctuates unpredictably and birds are unable to match reproductive output perfectly to food abundance. However, the degree to which predictable changes in food availability versus stochastic ones influence reproductive performance of seabirds is unknown. In this study we examined the role of food abundance prior to egg-laying versus food abundance during chick rearing for determining reproductive output of two species of high latitude nesting seabird; the Black-legged Kittiwake (Rissa tridactyla) and Common Murre (Uria aalge). We also examined the role of stress hormones in facilitating flexible reproductive effort. Here we demonstrate for the first time that initial reproductive performance (e.g., number of eggs laid, timing of egg-laying) is related to food abundance prior to egg-laying and not to anticipated food abundance during chick-rearing. We also demonstrate that stress hormones facilitate flexible reproductive effort-the failure of adults to increase stress hormone concentrations in response to an acute food shortage resulted in physiological and reproductive costs. Taken together, these results demonstrate that increases in stress hormone concentration are an adaptive response to breeding under variable foraging conditions. General introduction -- 1. Seabird timing of breeding and reproductive performance in relation to the seasonal dynamics of food abundance -- 2. Spatial and temporal heterogeneity in the dynamics of corticosterone and corticosterone-binding globulin in a free-living seabird -- 3. Failure to increase production of stress hormones lowers reproductive performance in kittiwakes (Rissa tridactyla) -- General conclusions.
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