Meeting Abstract
In socially monogamous birds, the hormone testosterone typically facilitates territorial aggression and nest defense, but in doing so, can suppress parental care. However, some species do not follow this pattern and it is unclear why, in these species, we do not see the predicted relationship between testosterone and behavior. One hypothesis is that the stress hormone, corticosterone can dampen activity of the hypothalamic-pituitary-gonadal axis and lower testosterone production. One potential stressor for adult birds is increased parental care. In our study population of eastern bluebirds (Sialia sialis), both males and females contribute to parental care, but parental behavior is not related to individual levels of testosterone in either sex. In 2014, we conducted a brood size manipulation from which we found that adults provided more parental care to enlarged broods. When the nestlings were 5-7 days old, we conducted parental care observations. When nestlings were 7-9 days old, we used a live house sparrow (Passer domesticus) to conduct a simulated territorial intrusion. Following each of these behavioral trials, we conducted gonadotropin-releasing hormone (GnRH) challenges on adults to quantify testosterone production capability. We measured both testosterone and the stress hormone, corticosterone, in blood samples, and related levels of these hormones to adult behavior and brood size. Testosterone is thought to mediate the trade-off between parental care and aggression, but not for all species. Studying how other hormones and life history traits interact with testosterone will help to uncover why some species seem to have become “behaviorally insensitive” to testosterone.
