Concentration of bat activity in riparian habitats over an elevational gradient

Riparian areas are generally assumed to represent important foraging areas for insectivorous bats, but this contention has rarely been formally quantified. To test this assumption, we used bat detectors to compare the relative activity levels of a community of temperate-zone bat species between riparian (lake) and upland (cutblock) habitats at three different elevations (ranging from 540 to 1800 m) in a forested area of southern British Columbia. In addition, we also investigated the sex and age class distributions of bats (based on mist-net captures) between riparian and upland habitats among the elevational zones. Bat activity levels were significantly greater in riparian than upland areas (10 and 40 times greater for foraging and commuting activity, respectively). Capture rates were greater in riparian areas and biased towards females, suggesting that female bats may preferentially select riparian areas, probably because of the abundant prey resources typically associated with this habitat. Captures of females also predominated at lower elevations, whereas males were captured more often in higher elevation zones. Our data support the assumption that riparian habitats represent important foraging and probably drinking areas for bats. The sex bias and differences in capture rates and activity levels need to be considered when designing bat surveys in different habitat types or over elevational gradients.