Effects of artificial light at night on activity of local bats. A field study from Slottsskogen Park, Gothenburg.

Abstract

Artificial light at night (ALAN) is a pressing issue on global biodiversity. Particularly sensitive are nocturnal animals such as bats. In this study, attempts were made to evaluate the effect of ALAN on the nightly activity of bat species who inhabit the area of Slottsskogen Park in central Gothenburg, Sweden. With the cooperation of Gothenburg City, the streetlights in six suitable sites within the park got a weekly alternating schedule of being lit and unlit, lasting four weeks. During this period, one bat detector was installed at each site, recording any passing bat sounds. The recordings were then analysed in BatSound, where each distinct individual per recording was marked down as a registration for the identified species. Activity was measured as the number of registrations per species and was then compared between light statuses. In total, six bat species were identified but only three of them had enough observations to be statistically tested reliably, those being Eptesicus nilssonii, Vespertilio murinus and Pipistrellus pygmaeus. The data of E. nilssonii and V. murinus showed a trend of preference for unlit sites, while the data of P. pygmaeus showed near equal activity levels for lit and unlit sites. However, testing showed nonsignificant effects of light status on the activity of any of the three species, possibly due to lacking sample sizes. While the results for E. nilssonii and P. pygmaeus match with pre-existing knowledge of these species, V. murinus appearing avoidant towards artificial light goes against the common notion that it, like most fast-flying bats, is relatively light-tolerant. Further research on the topic, and particularly on V. murinus, may have significant implications for conservational work.