Natal dispersal is a crucial life-history event which, at the individual level, represents an opportunity to move to high-quality breeding space associated with increased survival and reproductive success, and at the population level, underlies species distribution, population persistence, and gene flow. Despite its importance, dispersal is often treated as a random process owing to difficulties in monitoring movements of wild animals. Variation in dispersal is primarily driven by the balance between its costs and benefits, with benefits needing to outweigh costs of energetics, exposure to predators and competitors, and finding mates. This tradeoff is pronounced in cooperatively breeding species, in which offspring often delay dispersing from the natal territory. To investigate this complex behavior, I studied variation in natal dispersal and its components in an intensively studied population of Florida scrub-jays (Aphelocoma coerulescens), a cooperatively breeding species that specializes in a rare, fire-maintained oak scrub habitat endemic to Florida. By combining over 35 years of historical data and 5 years of field-collected data, I aimed to understand the drivers and consequences of natal dispersal in this population. I first summarized available data on dispersal patterns in this population, focusing on social and environmental factors related to variation in dispersal timing and distance. I then examined a previously overlooked pattern of dispersal called "staging" in which offspring disperse to join unrelated groups as nonbreeders. This behavioral variation explained some of the patterns previously uncovered, and exposed some proximate and ultimate drivers of dispersal. Next, using field methods along with laboratory work, I studied the physiological costs of prospecting, or information-gathering movements that precede dispersal. I found that prospecting results in oxidative damage, which is also regulated by early-life morphology and condition. Last, I quantified pre-breeding movements using newly developed tracking technology to understand how Florida scrub-jays explore their surroundings prior to dispersal. Combined, my chapters describe intraspecific movement and dispersal patterns, as well as some of their fitness consequences. Ultimately, my study of dispersal variation sheds new light on the complex nature of pre-breeding movement in a cooperatively breeding bird species, and contributes to the growing body of field and theoretical studies of this important life-history stage.

From 1988 to 2002 we studied the breeding ecology of Florida Scrub-Jays (Aphelocoma coerulescens) on John F. Kennedy Space Center/Merritt Island National Wildlife Refuge. We examined phenology, clutch size, hatching failure rates, fledgling production, nest success, predation rates, sources egg and nestling mortality, and the effects of helpers on these measures. Nesting phenology was similar among sites. Mean clutch size at Titan was significantly larger than at HC or T4. Pairs with helpers did not produce larger clutches than pairs without helpers. Fledgling production at T4 was significantly greater than at HC and similar to Titan. Pairs with helpers at HC produced significantly more fledglings than pairs without helpers; helpers did not influence fledgling production at the other sites. Nest success at HC and Titan was low, 19% and 32% respectively. Nest success at T4 was 48% and was significantly greater than at HC. Average predation rates at all sites increased with season progression. Predation rates at all sight rose sharply by early June. The main cause of nest failure at all sites was predation, 93%. Carter, Geoffry M. and Breininger, David R. and Larson, Vicky L. and Oddy, Donna M. and Smith, Rebecca B. and Stolen, Eric D. Kennedy Space Center NASA/TM-2005-212562...

Analysis of twenty years of historical reproductive data from our study population of Florida Scrub-Jays reveals a quadratic relationship between breeder age and number of fledglings produced, with the youngest and oldest birds having the lowest reproductive success. Such a decrease in reproductive performance in older birds, despite the likely benefits of increased experience, is often attributed to senescence. My dissertation research considered reproductive endocrinology, stress physiology, immunology, egg hatchability, life history trade-offs, and parental behavior. The oldest and youngest females have greater rates of hatching failure than middle-aged females. Results also indicate that circulating levels of reproductive hormones decrease with age in male Florida Scrub-Jays, but no such pattern was seen in females. Further, young and middle-aged males responded to a gonadotropin-releasing hormone challenge of their hypothalamo-pituitary-gonadal axis with a significant response of testosterone production, whereas old males did not. There were no significant differences among different aged birds in baseline stress hormone levels (corticosterone), however, the youngest and the oldest birds had a significantly greater magnitude of stress response than middle aged birds. There were also age-related differences in paternal care, as older male breeders consistently deliver more food to nestlings; however, there were no apparent physiological costs to do so (assessed with measures of corticosterone levels, innate immunocompetence, and body condition). The importance of biparental care was evinced as female breeders with mates who delivered more food strayed from the nest less often, and for shorter periods of time and female breeders that spent more time away from the nest were less likely to fledge young. Finally, a disease epidemic killed approximately 40% of the jays in our study population in 2008. Interestingly, older birds did not suffer greater mortality than any other age group, although surviving individuals all showed greater innate immune capabilities before the epidemic, providing a rare opportunity to show natural selection in a population of free-living animals. Combined, the results from the experiments and analyses of long-term demographic data show a comprehensive picture of age-related reproductive success, behavior, and underlying physiology in the Florida Scrub-Jay. .

Human activity may increase the perception of predation risk, thus suburban jays may take fewer, longer off-bouts or make fewer incubation feedings to decrease this perceived risk. These behavioral changes may increase nest temperature, thus increase embryo mortality. I placed thermocouples and video cameras at nests during incubation to gauge both ambient and nest temperature and behavior of scrub-jays at each site. I predicted higher ambient temperatures in the suburbs, because suburban areas often serve as heat islands. I also predicted fewer, longer off-bouts and fewer feedings in the suburbs and where human activity was increased experimentally. Ambient temperatures were higher in the suburbs as a result of higher daily minimums rather than higher maximums. Furthermore, females exposed to increased human activity took fewer but not longer off-bouts than suburban or wildland controls; therefore, they increased their nest attentiveness.