Official journal of the Netherlands Ornithologists' Union
|Wingfield J.C. & Ramenofsky M. (1997) Corticosterone and facultative dispersal in responses to unpredictable events. ARDEA 85 (1): 155-166
|Recent evidence suggests that facultative behavioural and physiological patterns in birds are triggered by unpredictable environmental events such as severe storms. These facultative patterns may involve finding a refuge ('shelter') until the perturbation passes, leaving the area and seeking other suitable habitat (e.g. irruptive-type migration). or a combination - seek a refuge at first and then if conditions remain inclement, seek other habitat. All these facultative events require that the individual retain sufficient fat reserves to either shelter ('ride-out') from the storm, leave a home range and forage nearby or, if suitable habitat is unlikely to be found close at hand, to fuel a flight of tens to hundreds of kilometres. Laboratory experiments in White-crowned Sparrows Zonotrichia leucophrys indicate that negative energy balance such as when a storm or other perturbation decreases food availability or intake, increased secretion of corticosterone. This in turn activates escape-like behaviour consistent with irruptive-type migration. Field studies confirm the elevated levels of corticosterone during inclement weather correlate with abandonment of nest sites in several species of sparrow, movements away from winter ranges when snow covers food resources, and alter movement patterns in seabirds. The steroid hormone corticosterone may play a major role in orchestrating facultative behavioural and physiological patterns (i.e. an 'emergency life history stage') to a variety of environmental perturbations. The resulting local movements, or irruptive migrations, are thus a form of facultative dispersal that may serve to maximise survival in the face of unpredictable and deleterious events in the environment.