Illuminating the physiological implications of artificial light on an insectivorous bat community

Global light pollution threatens to disturb numerous wildlife species, but impacts of artificial light will likely vary among species within a community. Thus, artificial lights may change the environment in such a way as to create winners and losers as some species benefit while others do not. Insectivorous bats are nocturnal and a good model to test for differential effects of light pollution on a single community. We used a physiological technique to address this community-level question by measuring plasma ß-hydroxybutyrate (a blood metabolite) concentrations from six species of insectivorous bats in lit and unlit conditions. We also recorded bat calls acoustically to measure activity levels between experimental conditions. Blood metabolite level and acoustic activity data suggest species-specific changes in foraging around lights. In red bats (Lasiurus borealis), ß-hydroxybutyrate levels at lit sites were highest early in the night before decreasing. Acoustic data indicate pronounced peaks in activity at lit sites early in the night. In red bats on dark nights and in the other species in this community, which seem to avoid lights, ß-hydroxybutyrate remained relatively constant. Our results suggest red bats are more willing to expend energy to actively forage around lights despite potential negative impacts, while other, generally rarer species avoid lit areas. Artificial light appears to have a bifurcating effect on bat communities, whereby some species take advantage of concentrated prey resources, yet most do not. Further, this may concentrate light-intolerant species into limited dark refugia, thereby increasing competition for depauperate, phototactic insect communities.