Proximate Mechanisms of Natal Dispersal: The Role of Body Condition and Hormones

We examine proximate issues related to the initiation of natal dispersal in birds and mammals, and focus in the interplay among hormone secretions and body condition in determining dispersal by individuals. In at least some mammals, early exposure to testosterone in males affects their subsequent dispersal, the timing of which is related to acquisition of a threshold level of body mass and body fat. Because in birds both sexes generally disperse, it is less likely that a gonadal hormone associated more with one sex that the other plays a major role in that process. Indeed, the adrenal hormone corticosterone has been implicated in the timing of avian dispersal. Increases in cortocosterone concentration near the time of dispersal come about either through endogenous or external mechanisms, and it is likely that these changes in hormone secretion are affected by attainment of body condition sufficient to disperse. Other substance, such as leptin, affect the hypothalamo-pituitary-adrenal axis, locomotor activity, and/or feeding behaviour, and may play a role in vertebrate dispersal.