LANDYS-CIANNELLI, M. M.; RAMENOFSKY, M.; WINGFIELD, J. C.; University of Washington, Seattle; University of Washington, Seattle; University of Washington, Seattle: The glucocorticoid-like receptor promotes feeding during spring migration and during energetic stress in the Gambel’s white-crowned sparrow (Zonotrichia leucophrys gambelii)

Plasma levels of corticosterone increase during the period of spring migration in a variety of bird species. Thus, corticosterone may play a role in the promotion of behavioral and physiological processes that characterize migration, such as migratory restlessness and energy mobilization. To determine the role of elevated levels of corticosterone during migration, we inhibited the glucocorticoid-like receptor (GLR) in photosensitive white-crowned sparrows (Zonotrichia leucophrys gambelii) placed on long days, and examined effects on feeding, locomotion, and plasma metabolites. We also tested the effects of GLR inhibition during winter and during a period of fasting. To our knowledge, this is the first study in birds to address the functional role of endogenously-elevated levels of corticosterone, rather than that of exogenously-administered corticosterone equivalents. We found that inhibition of the GLR suppressed food intake during migration but not during winter, and interfered with refeeding activities following fasting. Inhibition of GLR also reduced the mobilization of lipid stores in fasting birds. Contrary to our expectations, inhibition of the GLR did not affect activity, either during migration or during energetic stress, suggesting that corticosterone does not act through the GLR to regulate migratory restlessness or escape activity. In summary, our data suggest that in birds, the binding of corticosterone to the GLR promotes food intake and lipid mobilization, but does not influence locomotion.