The primary hormone involved in avian stress response is corticosterone (B), an adrenal steroid hormone. Previous studies have shown that environmental stressors (e.g., handling) cause an increase in corticosterone levels over time. I examined the adrenal response pattern in birds of different body conditions. Juvenile, female American kestrels (Falco sparverius) were maintained on one of three different diets, consisting of a control diet (fed ad libitum) and two calorically restricted diets, for six weeks. To invoke a stress response I captured the birds and held them in a cloth sack. I took blood samples at 1, 5, 10, 30, and 60 minutes after capture. all birds responded similarly to handling stress with an increase in plasma B, but control birds, (good body condition) showed a more rapid increase to maximum B levels, followed by a decrease in B after 30 minutes. Food-restricted birds had a slower rate of increase to maximum B and then maintained high corticosterone levels. These results suggest that birds in good physical condition respond quickly to stressors and adapt physiologically to stressful situations more rapidly than birds in poor physical condition. This difference may result from the ability of birds in good condition to mobilize fat for energy whereas birds in poor condition must mobilize protein (i.e., muscle).