DOI: 10.5061/dryad.3bc3s
title: Data from: Success despite the stress: violet-green swallows increase glucocorticoids and maintain reproductive output despite experimental increases in flight costs

description: Glucocorticoid steroid hormones play a central role in regulating the
 metabolic state of animals, especially when they cope with unanticipated
 stressors in their environment. The cort-adaptation hypothesis predicts
 that baseline concentrations of glucocorticoids are adjusted upward to
 match energetic needs and promote fitness when individuals are faced with
 physiological challenges, including those associated with reproduction. We
 tested the cort-adaptation hypothesis in the violet-green swallow
 (Tachycineta thalassina) by experimentally increasing flight costs during
 the offspring rearing period. Individual females were assigned to one of
 three treatments: light feather clipping (removal of four wing feathers),
 heavy feather clipping (removal of eight wing feathers) or a sham-clip
 control. We measured baseline corticosterone and body mass immediately
 prior to implementing treatments during the offspring rearing period and
 then 10 days after initial manipulations took place. We also quantified
 risk-taking behaviour, offspring feeding rate and the number of offspring
 fledged. Finally, we examined how treatments influenced offspring
 phenotype via measurements of nestling body mass and baseline
 corticosterone, as both measures have been associated with post-fledging
 survival. We found that handicapped females significantly increased
 baseline corticosterone between the two sampling periods, with the
 magnitude of change in the light clipping and heavy clipping treatments
 2·5× and 6·1× greater than controls, respectively. All individuals lost
 mass between the two sampling periods, but the degree of loss was greater
 for females in both clipping treatments relative to unmanipulated
 controls. In contrast, we found no evidence of treatment differences in
 female risk-taking, offspring provisioning or in the number of offspring
 fledged. Offspring raised by females in both handicapped treatments did
 have significantly elevated baseline corticosterone relative to those in
 control broods, but we detected no treatment differences in offspring body
 mass. Our study found that handicapped females increased circulating
 glucocorticoids and were able to maintain critical parental care
 behaviours and raise a similar number of offspring as unmanipulated
 controls. Thus, increases in baseline cort of handicapped females appeared
 to have allowed them to maintain fitness despite increased physiological
 challenges, providing support for the cort-adaptation hypothesis.
description: RiversetalVGSWHandicappingRawDataThis file contains data used to assess variation in pre-treatment measurements of adult females (tab1-tab2); data used to assess treatment effects on adult female baseline corticosterone, body mass, number of offspring fledged (tab3-tab4); data used to assess feeding rates by males, females, and males + females combined (tab5-tab7); data used to assess treatment effects on offspring body mass and baseline corticosterone (tab8); and data used to assess treatment effects on the time for females to enter nest boxes in the presence of a novel object (tab9).RiversetalVGSWhandicappingRawData.xls