Abstract:
Birds wintering in different climates may have different strategies for storing and using energy. We documented changes in body morphology and composition of Pacific Black Brant (Branta bernicla nigricans) wintering in Alaska and Baja California and modeled the energetic costs of wintering at each location. We compared costs associated with two different wintering strategies: 1) to remain in an unstable and harsh environment but close to breeding grounds, or 2) to migrate long distances to a mild environment, but distant from breeding grounds. Despite dramatic differences in the timing and magnitude of energetic costs between sites, Brant stored similar amounts of lipid and maintained similar body mass throughout winter. Brant operate under similar physiological bounds but changes in organ mass and nutrient storage took place within these bounds. This flexibility allowed Brant to employ two contrasting winter strategies. We suggest that there may be reproductive and energetic advantages associated with shortening migration distance and remaining in Alaska over winter. The number of Brant wintering in Alaska should continue to increase if constraints on food intake do not impede energy storage and survival is similar between sites.
