Postnatal glucocorticoid exposure causes long-lasting effects on competitive but not neophobic behaviors in a common...

Postnatal stress can affect behavior and physiology in vertebrates, but long-term effects of early-life stress experience are not well understood, especially in wild species. Glucocorticoids, steroid hormones that mediate a suite of physiological and behavioral traits in response to a changing environment, might play an important role in programming long-term responses. We examined the effects of early-life exposure to corticosterone, the primary avian glucocorticoid, on neophobic and competitive behaviors in the house sparrow (Passer domesticus). We manipulated circulating corticosterone levels in wild, free-living nestlings, then measured behavior at the juvenile and adult stages in captivity. Birds were independently tested on their response to a novel object (i.e., neophobia) and tested in their nest group on their response to a limited food source (i.e., competitive behaviors). We had alternate predictions: (1) corticosterone-treated birds would exhibit fewer neophobic behaviors and more competitive behaviors than controls if early-life corticosterone exposure adaptively prepares animals for high-stress environments; or (2) corticosterone-treated birds would be more neophobic and less competitive compared to controls if high early-life corticosterone exposure outpaces the organism's capacity to regulate stability. Additionally, we predicted that postnatal corticosterone exposure might affect juvenile behavior more than adult behavior if responses can be modulated by individual experiences over time. We found that early-life corticosterone exposure largely did not predict neophobic behaviors in response to a novel object and environment but did predict competitive behaviors in juveniles. Corticosterone-treated juvenile males tended to be less competitive and displaced more frequently than control juvenile males, whereas corticosterone-treated juvenile females tended to be more competitive than control juvenile females; however, these patterns were no longer present by adulthood. We conclude that early-life stress might have sex-specific effects in a bird's competitive ability in their first year of life, which could impact survival in populations facing novel stressors.