Temperature amplifies the effect of anthropogenic light on foraging common pipistrelle bats

Anthropogenic light affects the presence and behaviour of many species. Bats are generally repelled by light, but some fast-flying and agile species opportunistically forage on insects attracted to light sources. As insect activity is dependent on ambient temperature, prey abundance around light sources likely varies between cold and warm nights. Little is known on how the interacting effects of ambient temperature and anthropogenic light influence bat activity. We recorded activity of bats foraging around experimental light posts emitting different light spectra (white, green and red light) during 6 years for 2726 full nights to test how ambient temperature affects foraging activity of the abundant common pipistrelle (Pipistrellus pipistrellus). We found a strong interaction between light treatment and ambient temperature on the amount and timing of foraging activity. In warm nights, the total foraging activity increased near light posts, and the centre of foraging activity shifted towards the middle of the night. The interactive effect of ambient temperature on common pipistrelle bats foraging around anthropogenic light may contribute to shifts in food web interactions in warmer environments. This suggests that the ecological impact of anthropogenic light on bat biodiversity could be greater in warmer urban areas and warming climates.