Data from: A novel energy savings to multiple stressors in birds: the ultradian regulation of body temperature

The present study aimed to examine thermoregulatory responses in birds facing two commonly experienced stressors, cold and fasting. Logging devices allowing long-term and precise access to internal body temperature were placed within the gizzards of ducklings acclimated to cold (5°C) or thermoneutrality (25°C). The animals were then examined under three equal four-day periods: ad libitum feeding, fasting, and re-feeding. Through the analysis of daily as well as short-term, or ultradian, variations of body temperature, we showed that while ducklings at thermoneutrality show only a modest decline in daily thermoregulatory parameters when fasted, they exhibit reduced surface temperatures from key sites of vascular heat exchange during fasting. The cold acclimated birds, on the other hand, significantly reduced their short-term variations of body temperature while increasing long-term variability when fasting. This phenomenon would allow the cold acclimated birds to reduce the energetic cost of body temperature maintenance under fasting. By analyzing ultradian regulation of body temperature, we describe a means by which an endotherm appears to lower thermoregulatory costs in response to the combined stressors of cold and fasting.