The early life environment can have profound effects on an individual’s growth and development. Recent studies suggest that stress exposure in development has lifelong consequences in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis and the fitness of an individual. For my MSc, I am examining proximate and ultimate hypotheses regarding the effect of early-life environmental conditions in a winter breeding bird. Using Gray Jays as a model, I am combining field and laboratory techniques to determine if the early life history, including HPA axis activity, body condition, and the trophic level from which nestlings receive food, influences their recruitment into the population. I will also be examining how adult HPA reactivity influences reproductive performance.