The effects of 1, 2, 6 and 24 hours of fasting on hypothalamic-pituitary-adrenal axis function, body condition, and activity of wintering male white-crowned sparrows

Reductions in food resources or an animal's ability to forage can be greatly affected by perturbations of their environment such as weather events. In response to perturbations, animals activate the hypothalamic-pituitary-adrenal (HPA) axis in order to adjust physiology and behavior. The literature often makes the assumption that during weather events food intake declines leading to changes in HPA axis activity, including both basal and stress-induced circulating concentrations of corticosterone. We aimed to understand how varying lengths of fasting (1, 2, 6, and 24 hours), similar to what would be experienced by free-living birds compared to when food was proved ad libitum, affected body condition, locomotor activity, and stress physiology in captive male white-crowned sparrows, Zonotrichia leucophrys gambelii. Basal corticosterone concentrations were increased for all fasting durations but were highest in the 6 and 24 hour groups. Stress-induced corticosterone was elevated in the 1 hour group with a trend for the 2 hour group while no other differences were found. Basal corticosterone concentrations were negatively related to both total fat stores and body mass. All groups lost body mass during the fast with the 24 hour group losing the most. Fat stores declined in the 6 and 24 hour groups during the fast while no measureable changes were detected in muscle profile. Regardless of fasting duration, activity was increased over the entire period in which food was removed. Thus, it is likely that changes in food intake in the wild lead to rapid changes in HPA activity, fat stores, and activity.