Effects of artificial illumination on the presence of bat species

Abstract

Artificial light at night, or ALAN, is an issue that is gaining prominence around the world due to the continual urbanisation that is encroaching on natural areas. ALAN induces physiological impacts in insectivorous bats, as well as behavioural changes in the insects they consume, resulting in the bats exhibiting species and population- specific behavioural responses. The aim of this study was therefore to investigate the effects of artificial illumination on the presence of local bat species.

Acoustic monitoring was carried out for 24 nights in two sites located in Naxxar, Malta, one classified as the ‘dark’ site, which was not directly illuminated by ALAN, and one classified as the ‘illuminated’ site, which was directly illuminated by ALAN. Insect sampling using UV light traps was carried out in both sites for 15 nights. Kaleidoscope software was used to identify the bat signal recordings to species and genus level, and to quantify bat activity in the two sites. Analyses were carried out to statistically compare the differences in bat activity and insect presence between the two sites. Six bat species were identified from the ultrasonic recordings. The t-test analysis indicated statistically significant difference in bat activity for the bat species Hypsugo savii, showing higher activity in the illuminated site. Although no statistically significant differences were observed for the other bat taxa, the average nightly activity of Pipistrellus pipistrellus, traditionally a light-tolerant species, indicated higher activity in the dark site, while that of Pipistrellus kuhlii, also considered light-tolerant, indicated higher activity in the illuminated site, possibly indicating out-competition by the latter. The average nightly activity of Plecotus gasleiri and Myotis punicus, both considered light-averse, indicated higher activity in the illuminated site. The light-averse species, Rhinolophus hipposideros, showed higher nightly average activity in the dark site. The fact that most of the species exhibited higher activity in the illuminated site, even those considered to be light-averse, may indicate a local behavioural adaptation whereby local bat populations are being forced to withstand the ALAN, and the physiological effects that come with it, during foraging and commuting due to increased urbanisation and habitat fragmentation. These impacts on bat activity indicate a need for stronger ALAN guidelines and legislation locally to tackle the effects of urbanisation and protect darkened areas for local bat populations to thrive.