Light pollution at stadiums favors urban exploiter bats

Abstract

Artificial night lighting by humans may destabilize ecosystems by altering light-dependent biological processes of organisms and changing the availability of light and darkness as resources of food, information and refuge. I tested the hypothesis that urban exploiters should be more likely to utilize bright, unpredictable light pollution sources such as sport stadiums and building sites than urban avoiders. I quantified insectivorous bat activity and feeding attempts at seven sport stadiums under light and dark treatments using acoustic monitoring of echolocation calls. Species richness estimators indicated that stadium inventories were complete. Activity and feeding attempts were significantly higher at lit stadiums than dark stadiums, irrespective of season or surrounding human land use. Bats exhibited species-specific differences in utilization of stadiums. As predicted, four urban exploiters – Chaerephon pumilus, Tadarida aegyptiaca, Otomops martiensseni and Scotophilus dinganii – dominated activity and feeding attempts at lit stadiums, yet one urban exploiter – Mops condylurus – was associated with dark stadiums. Activity levels at both dark and light stadiums were negatively correlated with peak echolocation frequency. Landscape-scale and finer scale abiotic variables were poor predictors of bat activity and feeding attempts. My results suggest that in addition to abiotic processes associated with urbanization, light pollution at sport stadiums may homogenize urban bat diversity by favoring selected urban exploiters.