Meeting Abstract
44.1 Tuesday, Jan. 5 Seasonal energetics of a northern free-ranging mammal in a resource pulse system FLETCHER, Q.E.*; BOUTIN, S.; MCADAM, A.G.; SPEAKMAN, J.R.; HUMPHRIES, M.M.; McGill Univ. quinn.fletcher2@mail.mcgill.ca
Throughout the year, all animals face energetic demands resulting from allocation to reproduction, in addition to variation in food availability and climatic conditions. The role played by these energetic demands changes seasonally. Thus, to gain critical insight into the underlying factors affecting levels of energy expenditure, we examined seasonal changes in the field metabolic rate (FMR) of a natural population of red squirrels in Yukon, Canada. We focused on levels of energy expenditure during autumn food hoarding, winter, and lactation. Inter- and intra-annual variation in food availability and climatic conditions is extreme at this site. White spruce seeds that are hoarded during autumn are used preferentially to meet the energetic demands of winter and reproduction the following spring; however, seed is only available for a short window during autumn and seed production varies strongly among years. Moreover, the northern location of our study site exposes squirrels to extremely cold temperatures during winter, which potentially increases thermoregulatory demands. Levels of FMR varied strongly across seasons in adult female squirrels. Even though winter ambient temperatures were extremely low, the FMR of squirrels was at its lowest levels. Field metabolic rate was highest when red squirrels were hoarding white spruce seed, and these levels exceeded FMR levels during the peak of lactation. This was surprising because lactation is considered the most energetically demanding period of the year since females must obtain enough energy to meet their energetic demands in addition to those of their offspring. In conclusion, a seasonal comparison of FMR suggests that squirrels expend the most energy while accumulating the food capital that they use for winter and reproduction.
