Ontogeny of the stress response
Adults of many vertebrate taxa respond to physical, physiological, or emotional stress by turning on the hypothalamic-pituitary-adrenal (HPA) axis. The resultant rapid increase in serum glucocorticoid redirects physiology and behavior of the animal to help avoid further stress, thus increasing the chance of survival. These rapid effects of CORT include an increase in blood glucose level via gluconeogenesis, increases in foraging behavior and activity levels, and suppression of territorial behavior. However, when animals are exposed to persistent stress, elevated levels of CORT can have detrimental effects, such as disrupted reproduction, reduced immune function, damage to neuronal cells, and suppression of growth via suppression of growth hormone secretion (Sapolsky, 1992). Although both control and functions of CORT secretion have been well documented in adults, those of young animals, especially birds, have been largely ignored. It has been suggested that CORT may not be beneficial, or increase survival, in nestlings due to the negative effects of CORT on development and growth. Moreover, inability of the altricial young to move away from the nest and a stressor also implies that known beneficial effects of CORT may not apply to nestlings. On the other hand, changes in behavior, such as increased begging behavior in response to an increase in CORT, may be adaptive and favored by selection. This may be especially important in the case of storms or food shortage. The aims of this project are to determine the ontogeny of the stress response and to investigate the behavioral, physiological, and immune effects of the stress axis in nestlings.
White-crowned sparrow nestling
White-crowned sparrow nest