Vertical stratification of bat activity in an old-growth forest in western Washington

Abstract

We examined the amount and temporal patterns of bat activity at four different heights in an old-growth conifer forest at the Wind River Canopy Crane Research Facility in south-central Washington. Analysis of 2,304 bat passes showed that amount of activity differed among vertical strata. For Myotis bats, activity was greatest in the lower canopy, followed by the ground-level and upper canopy, respectively. We did not detect activity of Myotis above the canopy. Non-Myotis bats used lower and upper canopies more frequently than ground-level and above the canopy. Temporal patterns of activity generally exhibited a bimodal distribution, but the extent of bimodality and the time and relative size of peaks differed with species group and among heights. Activity was greatest at ground-level early in the night and later shifted to higher strata. Patterns of use of old-growth forests by bats may reflect the complex vertical structure of the vegetation in those forests. Exclusive use of ground-based equipment can result in an incomplete picture of the activity of bats in complex forest stands