Lean mass dynamics in hibernating bats and implications for energy and water budgets

Hibernation requires balancing energy and water demands over several months with no food intake for many species. Many studies have considered the importance of fat for hibernation energy budgets because it is energy dense and can be stored in large quantities. However, protein catabolism in hibernation has received less attention and whole animal changes in lean mass have not previously been considered. We used quantitative magnetic resonance body composition analysis to measure fat and lean mass in two systems of hibernating bats, emphasizing the importance of lean mass for energy and water budgets. For cave myotis ( Myotis velifer ), lean mass represented 38 and 25% (male and female respectively) of pre-hibernation mass gain. In Townsend’s big-eared bats ( Corynorhinus townsendii ), lean mass accounted for 18 – 35% of mass change during hibernation, but lean only contributed 3 – 7% of the energy budget. Water is produced from the catabolism of both fat and lean, but net water product...