Meeting Abstract
Rising global temperatures are generating new thermal challenges for animals across the tree of life. However, for endotherms, the sub-lethal behavioral effects of heat are poorly understood. Heat may be particularly inescapable in cavity-nesting birds, which are restricted to an enclosed area during a protracted but critical period of postnatal development. Here, we explore the behavioral effects of heat in nestling birds and test the hypothesis that nestlings behaviorally acclimate to heat. We experimentally simulated a 6-day heat wave inside the nest boxes of free-living tree swallows (Tachycineta bicolor) using air-activated shipping warmers that increased nest temperatures by >2°C. By measuring behavior only 4 hours after heat began and again 3 days later, we assessed the effects of both acute and persistent heat exposure. Sampling occurred when chicks were 6 and 9 days old, respectively, during the period of exponential growth. We quantified thermoregulatory behaviors that serve to expel heat, including the rate of panting and degree of clumping. In addition, we measured how heat exposure affects other fitness-related behaviors, namely, the frequency and intensity of begging. For both sets of behaviors, we assessed whether chicks acclimated to heat over time. Initial analyses show behavioral shifts in heated nests that may facilitate thermal tolerance, but treatments did not differ in nestling growth rates or survival to fledging. This study provides insight on how chicks behaviorally respond to thermal challenges and is an initial step in understanding how animals may cope with the increasing temperatures of climate change.
