RESUMO
The degree to which individuals adjust foraging behavior in response to environmental variability can impact foraging success, leading to downstream impacts on fitness and population dynamics. We examined the foraging flexibility, average daily energy expenditure, and foraging success of an ice-associated Arctic seabird, the thick-billed murre (Uria lomvia) in response to broad-scale environmental conditions at two different-sized, low Arctic colonies located <300 km apart. First, we compared foraging behavior (measured via GPS units), average daily energy expenditure (estimated from GPS derived activity budgets), and foraging success (nutritional state measured via nutritional biomarkers pre- and post- GPS deployment) of murres at two colonies, which differ greatly in size: 30,000 pairs breed on Coats Island, Nunavut, and 400,000 pairs breed on Digges Island, Nunavut. Second, we tested whether colony size within the same marine ecosystem altered foraging behavior in response to broad-scale environmental variability. Third, we tested whether environmentally induced foraging flexibility influenced the foraging success of murres. Murres at the larger colony foraged farther and longer but made fewer trips, resulting in a lower nutritional state and lower foraging success compared to birds at the smaller colony. Foraging behavior and foraging success varied in response to environmental variation, with murres at both colonies making longer, more distant foraging trips in high ice regimes during incubation, suggesting flexibility in responding to environmental variability. However, only birds at the larger colony showed this same flexibility during chick rearing. Foraging success at both colonies was higher during high ice regimes, suggesting greater prey availability. Overall, murres from the larger colony exhibited lower foraging success, and their foraging behavior showed stronger responses to changes in broad-scale conditions such as sea ice regime. Taken together, this suggests that larger Arctic seabird colonies have higher behavioral and demographic sensitivity to environmental change.
RESUMO
Many ecosystems have experienced anthropogenically induced changes in biodiversity, yet predicting these patterns has been difficult. Recently, individual behavioural and physiological measures have been proposed as more rapid links between environmental variation and fitness compared to demographics. Glucocorticoid hormones have received much attention given that they mediate energetic demands, metabolism, and foraging behaviour. However, it is currently unclear whether glucocorticoids can reliably predict environmental and fitness-related traits and whether they may be useful in specific groups of taxa. In particular, seabirds are a well-studied avian group often employed as biomonitoring tools for environmental change given their wide distribution and reliance on large oceanic patterns. Despite the increase in studies attempting to link variation in baseline corticosterone (the primary avian glucocorticoid) to variation in fitness-related traits in seabirds, there has been no comprehensive review of the relationship in this taxon. We present a phylogenetically controlled systematic review and meta-analysis of correlative and experimental studies examining baseline corticosterone as a predictor of fitness-related traits relevant to predicting seabird population health. Our results suggest that, while variation in baseline corticosterone may be a useful predictor of larger-scale environmental traits such as overall food availability and fitness-related traits such as reproductive success, this hormone may not be sensitive enough to detect variation in body condition, foraging effort, and breeding effort. Overall, our results support recent work suggesting that the use of baseline glucocorticoids as conservation biomarkers is complex and highly context dependent, and we suggest caution in their use and interpretation as simplified, direct biomarkers of fitness.
