Then versus now: effect of developmental and current environmental conditions on incubation effort in birds

The role of developmental conditions in shaping adult phenotypes has been the focus of a great deal of recent work. However, the effects of early life stress on reproductive performance have been little studied, particularly in avian species. In addition, although there is a large body of evidence to suggest that prevailing environmental conditions are linked to changes in breeding behavior, very little work has investigated the interaction between past and current exposure to environmental stress in determining breeding success. In this study, we examined the effects of early exposure to elevated stress hormone levels (corticosterone, CORT) on parental behavior during incubation in male and female zebra finches (<it>Taeniopygia guttata</it>) breeding in both stressful and nonstressful conditions as adults. We found that female birds fed CORT during postnatal development exhibited reduced incubation effort under both breeding conditions. There were no effects of developmental CORT exposure on male incubation effort; however, males breeding in unpredictable feeding conditions significantly reduced their effort levels compared with control males. There were no effects of either of our experimental treatments on hatching success or length of the incubation period. This may have been due to partial compensation by females paired with males that reduced effort. Our results clearly demonstrate sex-specific responses to developmental and adult environmental conditions in terms of incubation behavior and while in this captive population fitness costs appear to be ameliorated, birds breeding in a less benign environment in the wild may face higher costs having downstream effects on current or future reproduction.