Field metabolism and water flux of Carolina Chickadees during breeding andnonbreeding seasons: A test of the "peak-demand" and "reallocation" hypotheses

We tested the "peak-demand" and "reallocation" hypotheses of seasonal energ y expenditure which predict, respectively, that energy expenditure is great est during the breeding season or varies little seasonally. We rested these predictions by utilizing the doubly labeled water technique to estimate en ergy expenditure and water Bur of Carolina Chickadees (Poecile carolinensis ) in both the breeding and nonbreeding seasons. Similar to Weathers et al. (1999), we did not find support for either of these hypotheses, finding ins tead that energy expenditure was greater during the nonbreeding season. The fact that our study site was at the northern edge of the species' range, w here winters are severe, may have influenced this result. Comparisons with other parid studies were equivocal because body size was an important facto r in explaining seasonal energetics, and only the larger species have been examined during the breeding season.