The potential influence that environmental conditions experienced during early development may have on adult phenotypes has recently developed as an important research focus. While much of this work has centred upon the effects of variation in nutrient supply during pre- and post-natal development, another important axis to consider is the role of stress hormones, which are released in response to a range of adverse environmental and social conditions. The hypothalamic-pituitary-adrenal (HPA) axis responsible for the initiation and regulation of the physiological stress response undergoes significant development following birth in altricial bird species. It is thought that exposure to stress hormones may also alter the development of this axis and in so doing re-program the hormonal phenotype of the individual in adulthood, shaping behavioural and physiological responses to environmental stress, including resource allocation decisions during breeding. Using the zebra finch as a model species, this project will investigate the long-term and transgenerational effects of early exposure to stress hormones, specifically corticosterone (CORT). In particular, this research will examine the role of postnatal corticosterone exposure on the physiological and behavioural responses to a range of stressors in adulthood, as well as reproductive success, maternal transfer of corticosteroids and long term effects on offspring quality. We plan to use direct administration of corticosterone to avoid any problems with habituation to extraneous stimuli. By using a direct manipulation of nestling stress hormones we can focus on the long-term effects of early activation of the HPA axis, removing the confounding effects of other potential stressors such as changes in nutrient supply, which will cause multiple effects in addition to an activation of the HPA axis. A counterbalanced breeding experiment using same sex sibling pairs as a unit of comparison (one developmentally CORT treated, one control) will provide a powerful investigation of these possible effects in both males and females. The project will further address these issues under different environmental conditions, e.g. under favourable or unfavourable food availability, to determine the potential role of developmental CORT exposure in mediating appropriate responses under adverse conditions later in life. This study takes a multi-disciplinary approach, drawing on endocrinology, behavioural ecology and reproductive physiology, to determine if postnatal rearing conditions might be just as important as current conditions to the reproductive individual in decision-making. Radioimmunoassay techniques will be used to determine plasma corticosterone levels in response to stressors, at key points throughout an individuals life: during growth, early independence and whilst breeding. This research will therefore provide detailed information on how early life CORT exposure could program the physiology of a bird throughout its life. The proposed research fits perfectly within the remit of the Animal Sciences committee's Theme of 'Integrative Animal Physiology' as it addresses several of the issues identified in the Priority area of 'Genes to Physiology'. It will integrate behavioural and physiological information on the whole organism to understand the effects of neonatal programming on growth, behaviour and reproductive potential in adulthood, and provide valuable data on the role of early physiological experience in shaping an individuals response to it's environment.