Season and Migration Alters the Corticosterone Response to Capture and Handling in an Arctic Migrant, the White-Crowned Sparrow ( Zonotrichia leucophrys gambelii)

Abstract

The Gambel's race of white-crowned sparrow ( Zonotrichia leucophrys gambelii) migrates each year from their wintering grounds in the Southwestern United States to the Arctic to breed. Associated with this migration is a change in both the nonstressed and the stress-induced levels of circulating plasma corticosterone. Birds were captured at two sites on their wintering grounds (New Mexico and Arizona). Although stress-induced corticosterone levels were elevated at each site compared to nonstressed levels, there were no differences between wintering sites. These were also similar to levels in birds caught in Washington state during fall migration. In contrast, nonstressed corticosterone values were greatly elevated in birds on their breeding grounds in Alaska and similar to stress-induced levels in wintering birds. Corticosterone levels rose even further in response to the stress of capture and handling in breeding birds. These augmented corticosterone levels during breeding were not associated with weather. Both nonstressed and stress-induced corticosterone levels were similar in birds caught on their breeding grounds on two different years, one with temperatures during mid-May of approximately 0°C during a snowstorm and the other with temperatures in the mid-20s. These results suggest that seasonal physiological changes, and not local conditions, underlie seasonal changes in corticosterone levels. Furthermore, birds caught in Washington state during spring migration had intermediate levels of both nonstressed and stress-induced corticosterone. Corticosterone release may function differently during spring and fall migrations.