While much is known about the relationship between stress and the steroid hormone, corticosterone (CORT) in adult animals, less is known about the dynamics of CORT secretion in developing animals. My research examined factors affecting levels of baseline and stress-induced CORT in a free-living, non-migratory passerine, the Florida scrub-jay (Aphelocoma coerulescens ). I addressed the following questions: 1) Do baseline and stress-induced CORT secretion change with age? 2) Are nestling baseline CORT levels correlated with conditions in the nest, such as hatching order and parental behavior? 3) Are baseline and stress-induced CORT levels repeatable within individuals? 4) Do baseline and stress-induced CORT levels predict fitness? I found: 1) The degree of the stress response in nestlings was lower than that of nutritionally independent young and yearlings, although baseline CORT levels did not differ with age. 2) Baseline nestling CORT levels were inversely related to maternal nest attentiveness and paternal feeding rates. In broods of two, first-hatched nestlings had higher baseline CORT than second-hatched nestlings, although this pattern did not extend to broods of three or four. 3) Baseline CORT levels of individuals were not statistically repeatable over the course of the first several years of life. However, stress-induced CORT levels were repeatable, indicating that stress responsiveness is a stable aspect of the physiological phenotype. 4) Stress-induced CORT levels were not related to survival from one year to the next at any age. However, in one of three cohorts, baseline CORT at one year of age was inversely correlated with the probability of survival to two years of age. Many birds from this same cohort bred at the age of two, providing an opportunity to assess the relationship between CORT levels and measures of reproductive success. Baseline CORT levels and stress responsiveness during the pre-breeding period were predictive of some of these measures: birds with a higher stress response had fewer offspring survive to day 11 post-hatch and were less likely to fledge any offspring than birds with a lesser stress response. In addition, there was a positive correlation between pre-breeding baseline CORT levels and mean offspring mass on day 11 post-hatch.