Success despite the stress: violet-green swallows increase glucocorticoids and maintain reproductive output despite experimental increases in flight costs

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 q...