Data from: Heat dissipation capacity influences reproductive performance in an aerial insectivore

Climatic warming is predicted to increase the frequency of extreme weather
events, which may reduce an individual's capacity for sustained
activity due to thermal limits. We tested whether the risk of overheating
may limit parental provisioning of an aerial insectivorous bird in
population decline. For many seasonally breeding birds, parents are
thought to operate close to an energetic ceiling during the 2-3 week
chick-rearing period. The factors determining the ceiling remain unknown,
although it may be set by an individual 's capacity to dissipate body
heat (the heat dissipation limitation hypothesis). Over two breeding
seasons we experimentally trimmed the ventral feathers of female tree
swallows (Tachycineta bicolor, Vieillot, 1808) to provide a thermal
window. We then monitored maternal and paternal provisioning rates,
nestling growth rates, and fledging success. We found the effect of our
experimental treatment was context-dependent. Females with an enhanced
capacity to dissipate heat fed their nestlings at higher rates than
controls when conditions were hot, but the reverse was true under cool
conditions. Control females and their mates both reduced foraging under
hot conditions. In contrast, male partners of trimmed females maintained a
constant feeding rate across temperatures, suggesting attempts to match
the feeding rate of their partners. On average, nestlings of trimmed
females were heavier than controls, but did not have a higher probability
of fledging. We suggest that removal of a thermal constraint allowed
females to increase provisioning rates, but additionally provided
nestlings with a thermal advantage via increased heat transfer during
maternal brooding. Our data provide support for the heat dissipation
limitation hypothesis and suggest that depending on temperature, heat
dissipation capacity can influence reproductive success in aerial
insectivores.