PS 32-32
Field experiment to assess potential impacts of noise pollution on a bat community
Anthropogenic noise pollution can have negative effects on a wide range of taxa. Noise propagates far beyond areas of physical disturbance, causing acoustical fragmentation of what may be otherwise suitable habitat. The impacts of noise differ by species, and can manifest in many ways including changes in various behaviors, occupancy rates, predator-prey relationships, and ecological services. While the majority of studies investigating the effects of noise on wildlife have been single-species studies, a handful of songbird studies suggest that noise can cause changes at the community level. However, the impacts of noise have not been investigated in assemblages other than songbirds. Laboratory experiments show that noise can negatively affect foraging success of the European bat species Myotis myotis, but no experimental studies of bat assemblages exist to determine the effects of noise on bats in the field. Using 12 control sites and 12 noise propagation treatment sites in northwest Colorado, we experimentally isolated noise from other anthropogenic factors and asked: Does noise alone affect (1) species richness, (2) species composition, or (3) activity levels of free-flying bats in the field?
Results/Conclusions
During the 2013 season, we recorded more than 37,000 echolocation calls over all sites, representing 13 species of bats throughout the study area. We observed decreases in species richness and bat activity levels, and changes in species composition at treatment versus control sites. The mean number of species was greater at control sites (8.18) compared to treatment sites (6.18), and this difference was statistically significant (p = 0.003). Additionally, the mean number of calls recorded at control sites was higher than the mean number of calls recorded at treatment sites (p = 0.047). Two species (Myotis ciliolabrum & M. evotis) were recorded at all sites, however, three species were notably absent during noise treatment nights (Antrozous pallidus, M. californicus & M. volans). Antrozous pallidus uses a strategy called ‘gleaning’ to locate prey using passive listening. It is easy to imagine that this strategy could be susceptible to changes in the acoustical environment. M. californicus & M. volans are not considered obligate gleaners, making their apparent avoidance of noise treatment sites more unexpected. Ongoing data analysis from the 2013 and 2014 field seasons will provide further insights into these trends.