SYNOPSIS. Superimposed upon seasonal changes in morphology, physiology and behavior, are facultative responses to unpredictable events known as labile (i.e., short-lived) perturbation factors (LPFs). These responses include behavioral and physiological changes that enhance survival and collectively make up the "emergency" life history stage. There is considerable evidence that glucocorticosteroids, and other hormones in the hypothalamo-pituitary-adrenal (HPA) cascade, initiate and orchestrate the emergency life history stage within minutes to hours. This stage has a number of sub-stages that promote survival and avoid potential deleterious effects of stress that may result from chronically elevated levels of circulating glucocorticosteroids over days and weeks. These sub-stages may include: redirection of behavior from a normal life history stage to increased foraging, irruptivetype migration during the day, enhanced restfulness at night, and elevated gluconeogenesis. Once the perturbation passes, glucocorticosteroids may also promote recovery. Additional evidence from birds indicates that glucocorticosteroid responses to a standardized capture, handling and restraint protocol are modulated both on seasonal and individual levels. Field work reveals that these changes in responsiveness to LPFs have ecological bases, such as reproductive state, body condition etc., that in turn indicate different hormonal control mechanisms in the HPA cascade.