The effects of habitat quality and social dominance on (a) body mass and (b) blood hematocrit levels of male Black-capped Chickadees that were actively provisioning nestlings in central British Columbia.

These data suggest that dominant males are in better condition and have elevated metabolic rates. All males breeding in the young forest have elevated hematocrits, suggesting a physiological impact of habitat quality. In both graphs, means (± SE) are shown; however, the means in graph ‘a’ are standardized after controlling for tarsus size in an ANCOVA model.