Divergent responses of insectivorous bats and flying insects to experimental LED illumination of different spectra

Artificial light at night poses a global threat to biodiversity and is increasing at a rate greater than any other pollutant. We conducted a field experiment to investigate the effects of short-term nighttime illumination on nocturnal flying insects and insectivorous bats in previously unlit remnant bushland. We compared these organisms' responses to three types of light-emitting diode (LED) lights, each with a unique spectral composition (cool white [CW], λP 457 nm; filtered white [FW], λP 586 nm; and amber [A], λP 601 nm), as well as a control (C) group without illumination. Our findings revealed that both CW and FW LEDs significantly increased the total activity of flying insects, particularly the orders Diptera, Coleoptera, and Hymenoptera. By contrast, total bat activity was independent of light treatment, but there was a marginally non-significant effect on bats presumed to be light sensitive. Amber lights appear to mitigate the disruptive effects of light on at least one light sensitive bat species. Intriguingly, despite a positive association in one bat species with insect abundance, there was no corresponding increase in feeding activity around illuminated sites in this or any other species. These observations suggest that bats may not solely exploit the attraction of insects to LED lights as a feeding resource and that those species that persist in these environments are perhaps more light tolerant than light exploitive. Overall, our study highlights potentially complex responses of Australian insectivorous bats and flying insects to short-term LED lighting and contributes further insights into the ecological consequences of nighttime lighting.