Parental care Nest predation

Stress response a b s t r a c t Dependent young are often easy targets for predators, so for many parent vertebrates, responding to off-spring-directed threats is a fundamental part of reproduction. We tested the parental adrenocortical response of the endangered black-capped vireo (Vireo atricapilla) and the common white-eyed vireo ( Vireo griseus) to acute and chronic threats to their offspring. Like many open-nesting birds, our study spe-cies experience high offspring mortality. Parents responded behaviorally to a predator decoy or human 1– 2 m from their nests, but, in contrast to similar studies of cavity-nesting birds, neither these acute threats nor chronic offspring-directed threats altered plasma corticosterone concentrations of parents. Although parents in this study showed no corticosterone response to offspring-directed threats, they always increased corticosterone concentrations in response to capture. To explain these results, we propose that parents perceive their risk of nest-associated death differently depending on nest type, with cavity-nest-ing adults perceiving greater risk to themselves than open-nesters that can readily detect and escape from offspring-directed threats. Our results agree with previous studies suggesting that the hypotha-lamic–pituitary–adrenal axis, a major physiological mechanism for coping with threats to survival, prob-ably plays no role in coping with threats to offspring when risks to parents and offspring are not correlated. We extend that paradigm by demonstrating that nest style may influence how adults perceive the correlation between offspring-directed and self-directed threats.! 2009 Elsevier Inc. All rights reserved. 1