Meeting Abstract
Breeding birds may spend many weeks feeding their nestlings, resulting in a sustained increase in parental energy expenditure. But what sets the limit on how hard an individual works, especially if there are potential fitness benefits of raising more nestlings? The heat dissipation limit theory proposes that maximum sustained rates of energy expenditure are constrained by an individual’s capacity to dissipate metabolic heat (Speakman and Krol 2010). To test this, we studied breeding tree swallows, an aerial insectivore in which both parents forage for up to 15 hours per day. We predicted that if an individual’s capacity for sustained energy expenditure were limited by the risk of overheating, then individuals with increased capacity to dissipate heat would have higher nestling feeding rates. To increase heat dissipation capacity we experimentally increased the size of the brood patch in breeding females, by trimming the overlying feathers. Males do not have a brood patch and were un-manipulated. We also implanted temperature-sensitive passive integrated transponder (PIT) tags, which allowed us to monitor body temperature and feeding rates remotely. As predicted, females with experimentally enlarged brood patches had higher nest visitation rates than both un-manipulated females and males. These data support the hypothesis that risk of overheating limits parental provisioning performance in this species.
