Use of Tree Stumps as Roosts by the Western Long-Eared Bat

We report for the first time widespread use of loose bark on stumps in clearcuts as roosting sites by bats. We first discovered stump-roosting behaviour during the summer of 1993 when a radiotagged female western long-eared bat (Myotis evotis) roosted beneath loose bark on 4 separate stumps. During the summer of 1994 we searched for stump roosts in 11 south-facing clearcuts in the West Arm Demonstration Forest near Nelson, British Columbia. Nineteen roosts in 17 different stumps were located in 3 of the 11 clearcuts searched. Males and females accounted for 10 and 9 of the 19 roosts. Within clearcuts, bats selected large-diameter stumps, and tended to roost in southwest facing cavities. Temperatures of roost cavities were intermediate between those within randomly selected cavities and ambient temperatures. Temperatures within randomly selected cavities were significantly warmer than ambient temperatures, while those within roosts were not. Cavity temperature was related negatively to stump diameter, and cavities on the south side of stumps were relatively warm. We conclude that bats chose to roost in clearcuts to gain thermal benefits through increased exposure to sunlight and reflective heat, but within these clearcuts chose stumps that provided relatively cooler and more stable temperatures, presumably to avoid heat stress. Bats selected clearcuts with high proportions of uncluttered stumps, and stumps in clearcuts used by bats provided deeper cavities relatively far away from neighboring shrubs. Bats roosting in clearcuts may be subject to a trade-off between increased energetic savings and increased predation risk