ABSTRACT
Glucocorticoids modify metabolism and other physiological processes in order to mount an appropriate response to stress. This stress response is affected by a combination of seasonal changes, life-history events, and environmental factors. Determining seasonal variability and the potential connection between stress hormones and metabolism is fundamental in understanding seasonal physiological changes in animals. Here, we compared an indicator of stress (corticosterone) with an indicator of metabolic activity (uric acid-a non-enzymatic antioxidant and end product of protein metabolism) during capture and restraint in Northern Cardinals (Cardinalis cardinalis) during fall, winter, spring, and summer. Baseline corticosterone, the acute change in corticosterone (Δ10-corticosterone), and integrated corticosterone during capture stress were significantly different among seasons. For all corticosterone measurements birds captured in summer consistently had the lowest values while spring birds were highest. The lower corticosterone stress response in summer may decrease the likelihood of abandonment and thus protect investment in eggs/chicks. Higher glucocorticoid secretion in spring may benefit birds competing for nesting sites. No differences in uric acid levels (baseline, 60 min, and acute change over 60 min- Δ60-uric acid) were found among seasons. While plasma uric acid significantly decreased over an hour in all seasons examined, there were no significant correlations between baseline corticosterone and uric acid, time-60 corticosterone and uric acid, and Δ10-corticosterone and Δ60-uric acid. We conclude that the relationship between corticosterone and metabolism, as measured by uric acid, is indirect, and seasonal variation occurs with corticosterone secretion but not with uric acid, as measured here.
