Natural Disturbance Regimes as Templates for Boreal Forest Harvest

Although many species of bats select roost sites in large trees that are in open areas, intraspecific variation in roost-site selection may exist. We collected data on the roosting behaviour of little brown bats in the Cypress Hills, Saskatchewan, to determine the extent of intraspecific variation in roost-site selection. In addition, we examined the thermal microclimate of the tree-roosts selected by bats, to determine if roost-microsite variation can explain why certain cavities are selected over others. We found little brown bats roosting in trees as well as buildings. With the exception of a male who roosted in a spruce (Picea glauca ) stump, tree-roosts selected by male and female little brown bats were all in trembling aspen (Populus tremuloides ) trees. We found variation in roost-site fidelity and differential use of torpor by male bats. Temperatures within conifer snag cavities differed from aspen cavities during the day, and mirrored ambient temperature, which tended to be warmer than aspen cavities. We propose that bats select cavities in aspens because they are susceptible to heart rot. Aspen trees with heart rot provide cavities with an intact sapwood shell that protects bats against harsh ambient conditions as well as predators, and provides a unique thermal microclimate. Our results suggest that the origin of a roost site may be unimportant to a bat, provided certain other requirements are met.