Corticosterone manipulations alter morph-specific nestling provisioning behavior in male white-throated sparrows, Zonotrichia albicollis.

In the polymorphic white-throated sparrow (Zonotrichia albicollis), tan-striped males provision nestlings at higher rates than do white-striped males. In a previous study, we found that tan-striped males had lower baseline corticosterone levels than white-striped males during the nestling stage. To determine if this variation in corticosterone influences morph-specific differences in nestling provisioning behavior, we used intraperitoneal osmotic pumps to increase baseline corticosterone levels in tan-striped males (TS CORT) and administer RU486, a glucocorticoid receptor antagonist, in white-striped males (WS RU486). These manipulations essentially reversed morph-specific nestling provisioning behavior in males. TS CORT males fed nestlings at lower rates than TS controls (vehicle-only implant), and at similar rates to WS controls (vehicle-only implant), while WS RU486 males fed nestlings at higher rates than WS controls, and at similar rates to TS controls. These results demonstrate that (1) increases in baseline corticosterone (i.e., below concentrations associated with the adrenocortical response to stress) can directly or indirectly inhibit nestling provisioning behavior, and (2) corticosterone influences morph-specific variation in parental behavior in male white-throated sparrows. This study contributes to the growing evidence that modulating baseline CORT mediates parental care and self-maintenance activities in birds, and thus may serve as a mechanism for balancing current reproductive success with survival.