Year-to-year reuse of tree-roosts by California bats (Myotis californicus)in southern British Columbia

To document year-to-year reuse of roost trees by forest-dwelling bats we mo nitored trees in southern British Columbia that we first identified as mate rnity) roosts of California bats (Myotis californicus) in 1995. Initially w e identified roost trees by tracking radio-tagged individuals. Then we revi sited each tl ee in subsequent Fears up to 2000. At the start of the study the bars roosted under loose bark or in cavities in dead trees. Seven of ei ght trees were still standing in 2000, although all had lost bark since 199 5, particularly ponderosa pines (Pinus ponderosa). In 1995, after radio-tag ged bats had moved and the tags had fallen off, trees either M ere occupied by colonies of 5 to 52 M. californicus or they were unoccupied. In contras t, roost counts in subsequent)ears indicated that colonies rarely used the same trees and most observations were of one or two bats. Thus, while bats continued to use most of the trees ol er the 5 y period, the numbers of ind ividuals declined and much of the use may have been by males or non-reprodu ctive females. Although our study is preliminary, the results suggest that the suitability of roosts of tree-dwelling bats declines relatively rapidly compared to the loss of the snags themselves. More intensive studies are r equired given the current focus on preserving roosting habitat for forest-d welling bats.