Mitigating light pollution through motion-controlled LED lighting to protect bats

Light pollution is increasingly recognised as a pollutant that affects both humans and wildlife. Recently, an increasing number of roads and cycle paths have been illuminated by motion-controlled lighting, yet the adverse effects on nocturnal wildlife, such as bats, have so far prevailed. We investigated whether negative impacts could be mitigated by combining part-night lighting (switch off between 2300 and 500 h) with motion-controlled lighting and short lighting intervals using warm-colored light-emitting diodes (LEDs). Over a four-month period, we measured the acoustic activity of bats in several sections of a cycle path in two environments: a peri-urban area and an ecologically sensitive rural area. In the peri-urban section, we also tested whether 20-s light intervals had a lesser impact on bats than 40-s intervals. In the rural section, we tested whether amber light alleviates the adverse effects on sensitive forest-affiliated species. In the peri-urban area, the lighting scheme did not negatively impact bats, irrespective of the lighting duration. In the rural section, we observed that forest-specialist bat activity decreased in response to amber light at dusk but not at dawn. However, the activity of most other bat species remained unaffected. We conclude that a combination of part-night and motion-controlled lighting may mitigate the negative effects of artificial light on bats. However, we acknowledge that our study focused on a single bicycle trail. Furthermore, the negative response of forest-specialist bats to amber light emphasizes that even warm-colored LEDs can affect light-sensitive species — a problem that is likely to be exacerbated when trails are used more frequently. Using motion sensors to manage LED lighting on demand and switch it off completely in the middle of the night could be an effective way to reduce light pollution along bicycle trails, roads and in residential areas.