9509079 Natal dispersal, the movement from place of birth to location of first breeding, occurs in virtually all higher vertebrates. These movements have important implications for population regulation, mating systems, genetics, and conservation biology. The goal of this project is to understand the physiological ecology of natal dispersal movements in birds. A new model of dispersal, based on interactions among hormonal changes, body condition, and social stimuli, will be tested using both captive and free-living birds. The model predicts that level of corticosterone, a hormone known to stimulate increased locomotor and foraging activity, increases prior to dispersal due to a combination of endogenous and external events. This stimulates the locomotor activity that underlies dispersal behavior, and juveniles with sufficient fat reserves will disperse at that time. Birds in poor body condition will delay dispersing, but will increase their foraging activity. Dispersal of their siblings will reduce aggression and/or competition for food, enabling the remaining juveniles to improve their body condition and disperse. To test this model, hormone profiles of captive birds will be manipulated and their subsequent activity levels examined in relation to timing of dispersal. A second set of experiments will examine the relationship between corticosterone and timing of dispersal movements by free-living juvenile birds. These experiments will determine how activity levels, body condition, and hormones interact to control natal dispersal. This study will provide significant new insight into the factors controlling natal dispersal. The results will provide a basis for future studies of hormones and dispersal in vertebrates, and may be of applied value in managing the dispersal of species whose management is important.
