P1.208 Wednesday, Jan. 4 Low ambient temperatures may reduce cold endurance in wintering black-capped chickadees LEWDEN, Agnes; PETIT, Magali; VEZINA, Francois*; Université du Québec à Rimouski, Qc. Canada; Université du Québec à Rimouski, Qc. Canada; Université du Québec à Rimouski, Qc. Canada firstname.lastname@example.org
Regulation of body temperature is of premium importance for the maintenance of physiological functions in homeotherms. However, for small resident birds wintering at northern latitudes, heat loss is substantial and thermoregulation involves high energy demands. In some species, daytime body temperature (Tb) is known to decline during acute cold conditions. This can entail additional costs because a lower Tb may impair physiological functions and reduce alertness to predators. Winter cold acclimatization in these birds is associated with a seasonal increase in maximal shivering capacity (summit metabolic rate, Msum, measured under helox cold challenge), which is considered an indicator of cold endurance. Using black-capped chickadees wintering in eastern Canada as our model species, we hypothesized that birds with a higher thermogenic capacity would do better during cold days and would be less affected by ambient temperature in their capacity to maintain Tb constant during the day. From November 2010 to March 2011, we measured Tb at capture and Msum in free-living birds over a range wintering ambient temperatures (8°C to -22°C). Tb was negatively correlated to ambient temperature, with chickadees exhibiting a Tb 1-3°C lower during the coldest days. However, Msum was not related to Tb, when considering the effect of ambient temperature, but birds that had a lower Tb in the field attained their Msum earlier during the cold challenge. These results suggest that prolonged periods of cold temperature during winter may weaken cold endurance capacity in small resident passerines.