Impact of artificial lights on foraging of insectivorous bats in a Costa Rican cloud forest

Determining the effects of light pollution on tropical bat communities is important for understanding community assembly rules in urban areas. Studies from temperate regions suggest that, among aerial insectivorous bats, fast-flying species that forage in the open are attracted to artificial lights, whereas slow-flying species that forage in cluttered environments avoid those lights. We measured aerial insectivore responses to light pollution in a tropical cloud forest to test this hypothesis. Bat echolocation was recorded at 20 pairs of light and dark sites in Monteverde, Costa Rica. Foraging activity was higher at artificially lighted sites than dark sites near the new moon, especially around blue-white fluorescent lighting. Most recorded bat species showed increased or unchanged activity in response to light, including some slow-flying and edge-foraging bats. This finding suggests that, contrary to the evaluated hypothesis, flight speed and foraging mode are not sufficient to determine bat responses to artificial lights in the tropics. Two bat species showed decreased activity at light sites, and a low species evenness was recorded around lights, particularly fluorescent lights, compared with dark sites. As in the temperate zone, light pollution in the tropics seems to concentrate certain bat species around human-inhabited areas, potentially shifting community structure.