Impacts of forest harvesting on habitat use by foraging insectivorous bats at different spatial scales

Abstract

To assess habitat use by foraging bats in southern British Columbia, Canada, we used narrow band bat detectors and estimated insect availability with light-suction traps. We measured bat activity and insect availability in harvested forests at three spatial scales: habitat type (existing cutblocks, cutblock/forest edges, and undisturbed forest), stand age-class (four classes ranging between 80 and 250 years), and elevational zone (three zones ranging between 540 and 1800 m). In cutblock and edge habitat types, foraging activity paralleled insect availability, being greatest along edges. However, in the forest where insect availability was high we detected virtually no bat foraging activity. High foraging rates (foraging attempts/commuting passes) along edges indicated that bats foraged most efficiently in this habitat type. These results suggest that the spatial complexity of a habitat, in combination with insect availability, influences habitat use by foraging bats. There were no statistically significant differences in bat foraging activity or insect availability among the stand age-classes, but foraging activity by bats and insect availability decreased with increasing elevational zone. Our results suggest that the impact of forest harvesting on habitat use by foraging bats varies with spatial scale. Although edge habitat appears to be an important foraging habitat for some bats, the effects of forest fragmentation on bat populations or communities is currently unknown. Thus, the creation of edge habitat through forest harvesting cannot be considered a reasonable technique for managing bat populations.