The influence of residual tree patch isolation on habitat use by bats in central British Columbia
One forest management practice associated with logging aimed at contributing to the maintenance of biodiversity is to leave residual tree patches within cut blocks. Using Anabat bat-detectors we monitored bat activity along residual tree patch edges and clear-cut edges associated with recent clear-cuts in north-central British Columbia. We tested two hypotheses, (1) relative bat activity would be higher on the clear-cut edge than the residual patch edge, (2) relative bat activity would decrease on the residual patch edge with increasing isolation from the clear-cut edge. We sampled six pairs of edges and found no significant difference in bat activity between patch and clear-cut edges. We found a significant but non-linear relationship between relative bat activity on the patch edge with increasing patch isolation. Bat activity on the residual patch edge was highest at intermediate levels of patch isolation and lower both at patch edges close to, and highly isolated from the clear-cut edge. We postulate that the reason for this relationship is that patches act as windbreaks collecting high densities of insects making them good foraging areas but this benefit is coupled with an increased risk of prédation associated with crossing large gaps. At low levels of patch isolation bats may perceive residual patches and adjacent clear-cut edges as a continuous foraging area and thus, bat activity is evenly distributed throughout both habitats. In summary, our data indicate that patches provide localized habitat for foraging bats, however, foraging areas are only one habitat component required by bats and it remains uncertain if patches also offer suitable roosting opportunities.
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