Bat Activity, Insect Biomass, and Temperature Along an Elevational Gradient

Recent studies have documented high levels of bat fatalities at wind-energy facilities built on forested ridgetops in the eastern United States. To better understand the influence of temperature and elevation on bat activity levels, and the possible relationship of these factors to bat fatalities at wind facilities, we sampled bat activity and insect abundance along an elevational gradient at 3 study areas in northeastern Pennsylvania. Bat activity was sampled with an AR125 acoustic detector, and insect abundance was sampled with a black-light trap. We developed a negative binomial regression model to assess the relationship between bat activity and temperature, elevation, and insect abundance. We also assessed a hypothesized association between the occurrence of temperature inversions and increased bat activity at higher elevations. We found a significant positive association between bat activity and temperature (P < 0.001), with the effect of temperature being greater at higher elevations (P = 0.0211). Contrary to predictions, there was a significant negative relationship between bat activity and insect biomass (P < 0.001), and the association between bat activity and the occurrence of temperature inversions was not significant (P = 0.1). Although we did find significantly greater bat activity at higher temperatures, and an interaction between temperature and elevation, our results do not support temperature inversions as a factor in bat fatalities at wind-energy facilities on forested ridgetops in the eastern US.