Meeting Abstract
Body condition, an estimate of an animal’s fat reserves, is frequently used to assess population health and habitat quality, but few studies have attempted to link condition to individual survival. In deer mice, cold-induced summit metabolic rate is positively correlated with survival. Because fats are the primary fuel source for thermogenesis in rodents, an individual’s fat reserves (i.e., condition) may also be related to survival. We used a mark-recapture study to examine: 1) the relationship between condition and survival and 2) seasonal variation in body condition, activity levels, and field metabolic rate. We surveyed deer mouse populations on two 1-hectare grids in western Montana for four nights each month from May through November in 2018 and 2019. Body composition (percent fat and lean mass) was assessed via quantitative magnetic resonance (QMR). We did not find any association between percent body fat and survival rates over the sampling period. Female mice had higher percent body fat than males, but both sexes carried significantly less fat in August and September than in other months. Since this period represents the peak and tail of the dry season, this pattern may be linked to the hot and dry conditions of late summer. Deer mice are known to reduce aboveground activity when conditions are unfavorable, which could force individuals to rely on fat reserves in lieu of foraging. However variation in nightly movement rate was not significantly associated with month or percent fat – suggesting a different mechanism may be driving this seasonal reduction in fat reserves.
