Date of Award
Master of Science
Global light pollution is increasing worldwide, nearly doubling over the past 25 years, and the encroachment of artificial light into remaining dark areas threatens to disturb natural rhythms of wildlife species, such as bats. Artificial light impacts the behaviour of insectivorous bats in numerous ways, including changing foraging behaviour and altering prey selection. I conducted two manipulative field experiments to investigate effects of light pollution on prey selection in an insectivorous bat community. In the first experiment, I collected fecal samples from 6 species of insectivorous bats in naturally dark and artificially lit conditions and identified prey items using molecular methods. Proportional differences of identified prey were not consistent and appear to be species specific. Red bats, little brown bats, and gray bats exhibited expected increases in moths at lit sites. Beetle-specialist big brown bats had a sizeable increase in beetle consumption around lights, while tri-colored bats and evening bats showed little change in moth consumption between experimental conditions. Dietary overlap was high between experimental conditions within each species, and dietary breadth only changed significantly between experimental conditions in one species, the little brown bat. Our results, building on others, demonstrate that bat-insect interactions may be more nuanced than the common assertion that moth consumption increases around lights. Thus, no single policy is likely to be universally effective in minimizing effects of light pollution on foraging bats because of differences in bat and insect communities, and their interactions. Our work highlights the need for greater mechanistic understanding of bat-light interactions to predict which species will be most affected by light pollution, and to more effectively craft management strategies to minimize unnatural shifts in prey selection caused by artificial lights. In the second experiment, I again focused on changes in foraging due to light pollution by investigating expected knock-on physiological effects, which have not been studied. I measured plasma ß-hydroxybutyrate concentrations from six species of insectivorous bats in naturally dark and artificially lit conditions to investigate effects of light pollution on energy metabolism. We also recorded bat calls acoustically to measure differences in 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 followed by a decrease. Acoustic data suggest 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 constant, or possibly increased slightly throughout the night. Taken together, our results suggest red bats actively forage around lights and may gain some energetic benefit, while other species in the community avoid lit areas and thus gain no such benefit. Our results demonstrate that artificial light may have a bifurcating effect on bat communities, whereby a few species benefit through concentrated prey resources, yet most do not. Further, this may concentrate light-intolerant species into limited dark refugia, thereby increasing competition for depauperate insect communities, as insects are drawn to artificially lit spaces. It appears then that artificial lights change the environment in such a way as to benefit some species in insectivorous bat communities.
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