Meeting Abstract
Intraspecific brood parasites lay their eggs in the nests of other species for host parents to care for and raise. Adults or newly hatched young of many brood parasite species evict host eggs and/or nestlings from the nest. However, non-evicting brood parasites, such as the brown headed cowbird (Molothrus ater), are often raised alongside host nestlings. Biologists have long been fascinated by the evolutionary arms race between brood parasites and their hosts and the effects of brood parasitism on fitness. We know that parasitism reduces short- and long-term survival of host chicks and adults, particularly in small host species. However, there remain gaps in our knowledge concerning the proximate mechanisms that mediate host response to brood parasitism. Glucocorticoids (including the main avian glucocorticoid, corticosterone [CORT]) are released by activation of the hypothalamic-pituitary-adrenal axis in response to stress and mediate a number of nestling behaviors and metabolic processes. We examined circulating levels of baseline and stress-induced CORT levels in hooded warbler (Setophaga citrina) nestlings from brown headed cowbird parasitized and non-parasitized nests. Nestlings from parasitized nests had higher concentrations of baseline CORT compared to nestlings from non-parasitized nests. Parasitism did not affect stress-induced CORT levels. Elevated baseline CORT during development can interfere with growth, however, we found no difference in mass or tarsus length between nestlings from parasitized and non-parasitized nests. Our findings suggest that presence of or competition with cowbird nestlings is a stressor to host chicks. Further study is needed to determine if parasitized induced changes in CORT have downstream behavioral effects.
