Breuner, C. W.*; Hahn, T. P.: Corticosterone and inclement weather: mechanisms underlying adaptive behavioral responses in mountain birds.

In seasonally-breeding migratory birds, the drive to arrive early and establish a territory on the breeding grounds carries with it the potential benefit of improved reproductive success, but also the risk of encountering potentially life-threatening inclement weather. This is particularly true in species breeding at high elevations or high latitudes. Storms can reduce food availability, limit foraging opportunities, and impose increased thermoregulatory costs. Individuals� reproductive success can thus depend on how effectively they assess risks, and then modify behavior. In the High Sierra of California, mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) typically reach sub-alpine breeding areas in early May, when storms are common. Over the past 6 years, we have shown that when storm conditions become extreme, Z. l. oriantha typically abandon their territories and fly several kilometers to lower elevation, where conditions are milder and food is more abundant. Variation in internal reserves and/or food availability at the breeding site may modify the timing and duration of territory abandonment. We have evidence that corticosterone acts as an endocrine mediator between the environment and behavior during inclement weather. This system is proving ideal for studying the endocrine mechanisms that coordinate dramatic shifts in behavior in response to both external and internal factors. We have developed a working model of how several of these factors (weather, food availability, energy reserves, and corticosterone) interact to affect behavioral decisions.