Meeting Abstract
Parental provisioning of offspring is a labile behavioral trait that is expected to be shaped by tradeoffs during the current breeding attempt and/or through residual reproductive value. Experiments have shown that parents can change their provisioning in response to changes in the number of offspring, the contribution of a partner, or effort and/or risks involved in providing care. What is less well understood is how these behavioral changes are mediated physiologically, though corticosterone (CORT; as mediator of behavioral plasticity, particularly in response to stress), and prolactin (PRL; which is known to affect parental care) seem to be likely candidate hormones. To test these ideas, we transiently manipulated brood sizes in nesting pairs of house sparrows when nestlings were 7-8 days old, collected measures of parental behavior before and after the manipulation, and took blood samples, which were analyzed for CORT and PRL, after parents had adjusted to the new brood sizes. While pairs with reduced broods decreased their provisioning rates, circulating CORT did not differ among unmanipulated pairs, pairs with increased broods, and pairs with decreased broods. However, birds with higher CORT provisioned less overall and decreased their provisioning more following the brood manipulation. Changes in parental behavior may be mediated by interactions with PRL or other hormones. Additionally, for a subset of pairs we measured behavioral and CORT responses to a series of novel objects presented at the nest during provisioning in order to test whether sensitivity to changes in offspring demand was associated with sensitivity to environmental changes in the broader sense.
