BODY CONDITION AND THE ADRENAL STRESS-RESPONSE IN CAPTIVE AMERICAN KESTREL JUVENILES

We examined the adrenal response to handling stress of birds in differ ent body conditions. In order to affect the birds' body condition, you ng (73-d old) female American kestrels (Falco sparverius) were maintai ned for 6 wk on one of three diets: a control diet (fed ad lib.) and t wo calorically restricted diets. To invoke a stress response, we remov ed birds from their cages and took repeated blood samples over the cou rse of an hour. All birds responded to handling stress with an increas e in plasma corticosterone, but control birds (in good body condition) showed a more rapid increase to maximum corticosterone levels, follow ed by a decrease. Both groups of food-restricted birds had a slower ra te of increase to maximum corticosterone levels and then maintained hi gh corticosterone levels through 60 min. These results suggest that bi rds in good physical condition respond more quickly to stressors and a dapt physiologically to stressful situations more rapidly than do bird s in poor physical condition. This difference may reflect the ability of birds in good condition to mobilize fat for energy, while birds in poor condition must mobilize protein (i.e., muscle).