Control of behavioural strategies for capricious environments

In addition to seasonal changes in morphology, physiology and behaviour that occur in predictable annual cycles, there are facultative responses to unpredictable events known as labile (i.e. short-lived) perturbation factors. These rapid behavioural and physiological changes have been termed the 'emergency life-history stage' and serve to enhance lifetime fitness. There are four major components: (1) proactive/reactive coping styles for responding to psychosocial stress, predation, and so forth; (2) fight-or-flight responses to rapid emergencies such as an attack by a predator or sudden severe storm; (3) 'take-it-or-leave-it' behavioural and physiological responses to longer-term perturbations of the physical environment; and (4) sickness behaviour and fever designed to respond to infection. Glucocorticosteroids interact with cytokines and with other hormones in the hypothalamo-pituitary-adrenal cascade and in the autonomic nervous system to initiate and orchestrate the emergency life-history stage within minutes to hours. Some traits of the emergency life-history stage include: redirection of behaviour from a normal life-history stage to increased foraging, irruptive-type migration during the day, enhanced restfulness at night, elevated gluconeogenesis, and recovery once the perturbation passes. These physiological and behavioural changes allow an individual to avoid potential deleterious effects of stress that may result from chronically elevated levels of circulating glucocorticosteroids over days and weeks. Thus, acute rises in glucocorticosteroids following perturbations of the environment may serve primarily as 'antistress' hormones, potentially allowing individuals to avoid chronic stress. Several field studies in diverse habitats indicate that individuals in free-living populations show elevated circulating levels of corticosteroids when they are in an emergency life-history stage. Some simple models based on food availability, body condition, social status and life-history stage, may allow predictions of sensitivity of the hypothalamopituitary-adrenal axis to labile perturbation factors. Although there is now extensive evidence for behavioural components of the emergency life-history stage in birds, there remains much to be learned about how other vertebrate groups, especially fish, cope with perturbations of the environment. Because of the unpredictable nature of these perturbations, systematic study of behavioural responses to them is not possible and investigators need to be 'opportunistic'. There is also a growing need to expand our knowledge of these phenomena because human disturbance, global climate change and pollution are all major perturbations of the environment. How vertebrates respond to the unpredictable in general will thus have important conservation value for the future. (C) 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.