Flushing effects and seasonal changes on corticosterone levels in adult Long-Eared Owls Asio otus

Abstract

Long-eared Owls Asio otus were flushed and captured from communal winter roosts and nesting seasons to assess both initial and stress-induced corticosterone concentrations. We examined blood samples from 16 males and 8 females in the winter, and 16 males and 11 females in the breeding season. Corticosterone concentrations after flushing owls in either season were not correlated with the elapsed time from initial flush to capture, suggesting that these birds did not interpret flushing as stressful. In contrast, 30 min of handling and restraint during both seasons elicited robust increases in plasma corticosterone concentrations that did not differ by sex. Although stress-induced corticosterone levels did not differ seasonally, baseline levels were 50% lower during the winter compared to breeding, suggesting the breeding season is a more stressful time. These results indicate that capture techniques used in this study with Long-eared Owls were only stressful when successful, and that initial corticosterone concentrations vary seasonally.