Meeting Abstract

9.8  Sunday, Jan. 4  Effects of brood size on chick-feeding rates, growth and corticosterone in nestling tree swallows PARSONS, RL*; VLECK, CM; Iowa State Univ., Ames bparsons@iastate.edu

Studies in birds have found that poor nutrition during development can cause reduced growth and elevated corticosterone (CORT) levels in chicks that have long-term negative effects on fitness and cognition in adulthood. This study addressed the question of how natural variation in brood size relates to patterns in early growth and development and CORT levels in tree swallows. Large brood sizes may result in decreased food delivery per chick resulting in reduced growth and elevated CORT levels. Tree swallows provide an ideal system in which to address this question because brood size can vary from one to eight chicks. Unless parents modify their chick-feeding rate to compensate for larger broods, we predicted that such variation should affect food delivery rates to nestlings, their subsequent growth and baseline CORT levels. In the summers of 2007 and 2008 we monitored adult food delivery rates to 61 nests and chick growth rate and CORT levels in a total of 250 chicks, using broods that varied from one to seven chicks. Chick-feeding rates increased as brood size increased, but the feeding rate per chick decreased. Brood size had a negative effect on chick growth; asymptotic mass of chicks from small broods averaged 22.3g and chicks from large broods averaged 21.3g. At the same time, neither baseline CORT nor CORT levels after handling stress varied with brood size, although chicks in poor condition did have elevated basal CORT levels. Within the normal range of brood sizes adult tree swallows appear able to provide adequate nutrition for chicks, as indicated by low baseline CORT, even though brood enlargement results in smaller chicks. Small chick size is linked to reduced survival in other passerine species; the effect of small chick size on survival is not known in this population.