Meeting Abstract
Acclimatization to winter cold in small northern resident bird species is typically associated with increases in maximal shivering thermogenic capacity (summit metabolic rate, Msum) and physiological maintenance costs (basal metabolic rate, BMR) as well as with an enlargement of internal organs. It is believed that enlarging flight muscles in winter is a mechanism for improving cold endurance while larger supporting organs such as those used for energy acquisition are responsible for variation in maintenance costs. However, studies directly testing these assumptions are few and provide mixed support. We studied differences in body composition of captive black-capped chickadees (Poecile Atricapillus ) acclimated for a month to -10°C or 26°C and investigated how the mass of individual organs were related to metabolic performance. As expected, cold acclimated birds had an Msum 20% higher than those kept at thermoneutrality. However pectoral muscles did not differ between temperature treatments. In contrast, BMR was 9% higher in cold acclimated birds and those also had digestive organs (liver, intestine, pancreas) up to 56% larger in the cold. Our preliminary results therefore suggest that temperature related changes in digestive organs might be related to maintenance costs variation in captive chickadee. They also suggest that these birds are able to improve thermogenic capacity without changing their muscle size.
