CORTICOSTERONE AND THE STRESS-RESPONSE IN YOUNG WESTERN SCREECH-OWLS - EFFECTS OF CAPTIVITY, GENDER, AND ACTIVITY PERIOD

We used a standard handling protocol to examine the stress response of captive young western screech-owls during their active (nighttime) an d inactive (daytime) periods and to compare the stress responses of ca ptive and free-living owls. Circulating corticosterone levels were sig nificantly higher during the inactive period than in the active period in this nocturnal species. This suggests that the daily pattern of co rticosterone secretion is reversed in nocturnal birds and is correlate d with activity period rather than with the light/dark cycle. Young (c a. 4-5 mo old) screech-owls of both sexes showed increases in plasma c orticosterone up to 30 min after capture, followed by significant decr eases at 60 min. This pattern is similar to those of other species of birds examined previously, except that decreases in corticosterone at 60 min rarely have been observed. Such decreases may be the result of physiological differences between adult and young birds, habituation t o handling in captive birds, or the effects of body condition. Cortico sterone levels and the response to capture and handling were comparabl e in captive and free-living owls, which suggests that the captive owl s were not subjected to chronically high levels of stress.