Meeting Abstract
When homeostasis is disrupted, vertebrates respond by activating the hypothalamic-pituitary-adrenal (HPA) axis, which leads to the release of glucocorticoids (GC). GCs, including corticosterone (CORT, the main avian GC), are steroid hormones that serve a crucial role in the response to and recovery from stress. The development of the CORT response can depend on the life history strategy of a species. For instance, the developmental hypothesis predicts that altricial young have a dampened CORT response, because nest-bound young likely do not benefit from the escape and post-escape actions of CORT. However, there is a lack of comparative studies that assess possible variation in CORT response among altricial species with different life history strategies. We compared the development of the CORT response in a brood parasite passerine, the brown-headed cowbird (Molothrus ater), and five non-parasitic passerines to determine if the magnitude and development of the stress response differs. We quantified baseline and stress-induced CORT levels from blood samples collected throughout the nestling period. The magnitude and development of the stress response of cowbirds was similar to those of eastern phoebes (Sayornis phoebe), hooded warblers (Setophaga citrina), red-winged blackbirds (Agelaius phoeniceus), and song sparrows (Melospiza melodia). Surprisingly, the CORT response of gray catbirds (Dumetella carolinensis) was significantly lower throughout the nestling phase. Overall, our results support previous findings that passerine nestlings have a dampened CORT response that develops with age. We did not find evidence that the development of the HPA axis in a brood parasite species differed from most non-parasitic passerines. However, the especially low CORT responsiveness of catbird nestlings raises new questions about their development and possible life history strategies.
