Presence, relative abundance, and resource selection of bats in managed forest landscapes in western Oregon

I studied presence, relative abundance, and resource selection of bats in managed Douglas-fir (Pseudotsuga menziesii) forests in western Oregon from May through September, 1999--2001. Species richness was not related to elevation, density of snags, or length of edge or perennial streams in sampled landscapes. I captured bats more frequently in landscapes with moderate to high densities of snags and sex ratios were skewed toward males, especially in snag-rich landscapes at higher elevations. Elevation generally was negatively related to captures of female bats. I determined use of day roosts by female and male long-eared myotis (Myotis evotis ), female long-legged myotis (Myotis volans), and female big brown bats (Eptesicus fuscus). Relative to random structures, all three species used snags that had less canopy closure, more adjacent snags, and were closer to the edge of the stand. Diameter of snags was an important variable differentiating roost and random snags used by big brown bats and long-legged myotis. I found considerable overlap in structural and contextual characteristics of snags and trees used as roosts among the three species of bats. My findings provide evidence that females of sympatric species of bats may alter their choices of roosts when co-existing in landscapes with low densities of snags. Female and male long-eared myotis primarily used stumps and down logs in landscapes with low densities of snags, while using snags more frequently in landscapes with high snag densities. I found that tree species and structural characteristics of snags, stumps, and logs used as roosts generally were similar between female and male long-eared myotis and that context variables (e.g., elevation) best differentiated use of structures between sexes. Failure to account for differences in use of roosts among species, between sexes, and among landscapes with varied conditions could lead to erroneous conclusions and ineffective or inappropriate management recommendations. Elevational gradients and densities of snags are important factors to consider when developing snag and green tree retention strategies for bats in this region. Forest management practices that retain and create large snags in landscapes currently with low densities of snags would benefit female bats, especially at lower elevations.