Intra- and interspecific patterns of day roost selection by three species of forest-dwelling bats in Southern British Columbia

Abstract

We examined intra- and interspecific patterns of roost-site selection by females of three species of forest-dwelling bats (silver-haired, Lasionycteris noctivagans; big brown, Eptesicus fuscus; and California, Myotis californicus) in the Pend d’Oreille Valley in southern British Columbia. Roost-sites were located by outfitting reproductive and non-reproductive female bats with radio-transmitters and tracking them during the daytime. The tree and site characteristics of roost trees used by each bat species were then compared to those of randomly available trees with cavities, as well as to each other, using logistic regression. All three bat species selected roosts that were taller than cavity trees, and the majority of roost trees were emergent or canopy trees. In addition, tree species and the type of cavity were important predictors of whether trees were used as roosts in both intra- and interspecific analyses. The majority of silver-haired and big brown bat roost trees were in hollows in live trembling aspen trees ( Populus tremuloides), but both species used small numbers of roosts on conifer snags. In contrast, the majority of California bat roosts were beneath loose bark on conifer snags, particularly Douglas-fir ( Pseudotsuga menziesii), in intermediate stages of decay. In general, site characteristics were only weak predictors of differences between roost and random trees, and roost trees used by the three bat species, but roost trees were found in patches with lower percent canopy closure and greater density of available trees. These results suggest that while all three species of forest-dwelling bats use large trees, within this restricted range of trees there is considerable variation among species in the types of cavities and the tree species used. Maintaining stands containing mature trembling aspen is necessary to provide silver-haired and big brown bats with suitable roosting opportunities, but to meet the needs of California bats, areas rich in conifer snags must be protected. Thus, unique management strategies or silvicultural practices may be required to maintain suitable habitat for all bat species in a given area.