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-roosti ng behaviour during tile summer of 1993 when a radiotagged female west ern long-eared bat (Myotis evotis) roosted beneath loose bark on ii se parate 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 accounte d for 10 and 9 of the 19 roosts, within clearcuts, bats selected large -diameter stumps, and tended to roost in southwest facing cavities. Te mperatures of roost cavities were intermediate between those within ra ndomly selected cavities and ambient temperatures. Temperatures within randomly selected cavities were significantly warmer than ambient tem peratures, while those within roosts were not. Cavity temperature was related negatively to stump diameter, and cavities on the south side o f stumps were relatively warm. We conclude that bats chose to roost in clearcuts to gain thermal benefits through increased exposure to sunl ight and reflective heat, but within these clearcuts chose stumps that provided relatively cooler and more stable temperatures, presumably t o avoid heat stress, Bats selected clearcuts with high proportions of uncluttered stumps, and stumps in clearcuts used by bats provided deep er cavities relatively far away from neighboring shrubs. Bats roosting ill clearcuts may be subject to a trade-off between increased energet ic savings and increased predation risk.