To determine the influence of habitat complexity on bat activity, we investigated search-phase calls and feeding-buzz calls of bats across a diverse array of palustrine habitats in the northern Great Lakes region. We surveyed 40 sites acoustically for bats in summer 2007 using AnaBat II detectors. We also measured vertical (total vegetation volume and Levins diversity index) and horizontal (canopy cover, area of open water) structural complexity. We recorded 5,866 search-phase calls or bat passes and 725 feeding buzzes--representing all six species that occur in the region--at 39 sites. We identified Little brown bats (Myotis lucifugus LeConte) most often (76.4%). Regressions of bat activity measures with habitat structure metrics suggest that either canopy cover or area of open water were influential predictors of relative activity for Little brown and Red bats (Lasiurus borealis Muller) or presence of the remaining four species. In contrast, measures of vertical habitat complexity did not appear to influence community composition of bats. However, the number of feeding-buzz calls relative to the number of search-phase calls was higher in areas with less vegetation volume and greater canopy cover. Although structural complexity was influential in explaining bat activity in palustrine habitats, we suggest that other environmental or biological factors also may be contributing to observed patterns of bat activity. INTRODUCTION
