Townsend's big-eared (Corynorhinus townsendii) bat is a medium sized cave dwelling bat. It is a slow flying but maneuverable bat that eats mostly moths. Distinguishable features include its large ears and 2-pronged lump on its nostrils. Townsend's big-eared bats occur throughout North America from British Columbia to Mexico. Their habitat can vary widely as long as caves or cave-like roosting habitat can be found in an area. Big-eared bats are typically found roosting singularly with the exception of winter months when both sexes hibernate together in groups of up to several hundred bats and in summer maternity roosts where only females and their young roost together. Unlike other bats that prefer to hide in crevices while roosting, Townsend's big-eared bats can be found in groups on open surfaces inside of caves. Roosting in open surfaces makes these bats vulnerable to disturbances.
In Idaho, there are two subspecies of Townsend's big-eared bat, Corynorhinus townsendii townsendii which can be found in the western part of the state while Corynorhinus townsendii pallescens is found in the eastern part of the state. Although many populations are found in historic mining districts, the largest populations have established themselves in the lava flows in southeastern Idaho. As of 2008, three of the four maternity colonies known in Idaho are found in the lava tubes here at Craters of the Moon.
At Craters of the Moon, the National Park Service (NPS) identifies critical habitat use patterns of Townsend's big-eared bats as well as monitoring the occupancy and abundance of these bats in the lava tubes.