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 (change
of 6°C and 8°C), bats would likely starve before hibernation ended.