KELLY, Scott A.; TOMASI, Thomas E.; University of California, Riverside; Southwest Missouri State University: Ambient Temperature Effects on Metabolism and Body Composition in Torpid Bats (Myotis lucifugus and Pipistrellus subflavus)

Recent declines in Indiana bat (Myotis sodalis) populations have been well documented but unexplained. It is unclear if declines are caused by exposure to and accretion of environmental contaminants, the loss of summer roosting habitat, changes in cave microclimate, or other detrimental factors. An inverse relationship between temperature and stable populations of M. sodalis has been observed within hibernacula. An increase in cave temperature should result in an increase in metabolic rate during torpor. Without the ability to minimize metabolic needs, irreplaceable energy reserves could become depleted, resulting in death or insufficient energy to reproduce in the spring. To address causation, a study was conducted on ambient temperature effects on metabolism and body composition in two species of bats (Myotis lucifugus, Pipistrellus subflavus), which are sympatric with M. sodalis and are not endangered. Bats were collected and housed in an environmental chamber that mimicked photoperiod, temperature and humidity of their natural hibernacula. Metabolic measurements were made with an open flow-through oxygen analyzer and data acquisition system at varying ambient temperatures. Using temperatures ranging from 6^°C to 16^°C, metabolic rates were lower and apnic periods during torpor were longer at lower temperatures. Body fat composition analysis revealed that if ambient temperature increased (3^°C) all surplus fat could be utilized by the end of hibernation, leaving none for reproduction. At higher ambient temperatures (Δ6^°C and 8^°C), bats would likely starve before hibernation ended.