Effects of weather on corticosterone responses in wild free-living passerine birds.

Harsh weather can have devastating effects on both the survival and the breeding success of wild animals. Corticosterone, released in response to the stress caused by harsh conditions, may trigger physiological and behavioral changes that help ameliorate these effects. We examined three species of Arctic-breeding passerine birds for correlations between circulating plasma corticosterone levels and weather conditions at the time of capture. Furthermore, because persistently poor weather conditions may be required to initiate a stress response, we also looked for a relationship between corticosterone levels and weather conditions over the 24 and 72 h preceding capture. None of the three species showed substantial effects of weather on unstressed corticosterone levels during the breeding season, although one species showed a significant relationship with stress-induced corticosterone levels. In two species, however, variations in weather during molt (an energetically costly period when birds replace their feathers) explained from 35 to 88% of the individual variation in corticosterone levels. In a third molting species, weather conditions in the preceding 24 and 72 h explained between 20 and 30% of the individual variation in corticosterone levels. It thus appears that adverse weather may be a potent stimulator of corticosterone release during molt, but not during the breeding season. Although extreme weather conditions (those experienced once every few years) can disrupt breeding, since none of the birds abandoned breeding we might conclude that the storms in this study were well within the ability of the birds to cope physiologically.