To document year-to-year reuse of roost trees by forest-dwelling bats we monitored trees in southern British Columbia that we first identified as maternity roosts of California bats (Myotis californicus) in 1995. Initially we identified roost trees by tracking radio-tagged individuals. Then we revisited each tree in subsequent years up to 2000. At the start of the study the bats roosted under loose bark or in cavities in dead trees. Seven of eight trees were still standing in 2000, although all had lost bark since 1995, particularly ponderosa pines (Pinus ponderosa). In 1995, after radio-tagged bats had moved and the tags had fallen off, trees either were occupied by colonies of 5 to 52 M. californicus or they were unoccupied. In contrast, roost counts in subsequent years 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 over the 5 y period, the numbers of individuals declined and much of the use may have been by males or non-reproductive 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 required given the current focus on preserving roosting habitat for forest-dwelling bats.
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Vol. 146 • No. 1