Experimentally manipulating light spectra reveals the importance of dark corridors for commuting bats

Abstract

The rapid global spread of artificial light at night is causing unprecedented disruption to ecosystems. In otherwise dark environments, street lights restrict the use of major flight routes by some bats, including the threatened lesser horseshoe bat Rhinolophus hipposideros, and may disrupt foraging. Using radio tracking, we examined the response of individual female R. hipposideros to experimental street lights placed on hedgerows used as major flight routes. Hedgerows were illuminated on one side over four nights using lights with different emission spectra, while the opposite side of the hedge was not illuminated. Automated bat detectors were used to examine changes in overall bat activity by R. hipposideros and other bat species present. R. hipposideros activity reduced significantly under all light types, including red light, challenging a previously held assumption that red light is safe for bats. Despite this, R. hipposideros rapidly adapted to the presence of lights by switching their flight paths to the dark side of the hedgerow, enabling them to reach foraging sites without restriction. Red light had no effect on the activity of the other species present. Slow‐flying Myotis spp. avoided orange, white and green light, while more agile Pipistrellus spp. were significantly more active at these light types compared to dark controls, most probably in response to accumulations of insect prey. No effect of any light type was found for Nyctalus or Eptesicus spp. Our findings demonstrate that caution must be used when promoting forms of lighting that are thought to be safe for wildlife before they are tested more widely. We argue that it is essential to preserve dark corridors to mitigate the impacts of artificial light at night on bat activity and movements.

Artificial light may change flight patterns of bats near bridges along urban waterways

“…The considerably lower number of bat passes found near illuminated bridges, and the increase in flight speed in response to light is particularly interesting as Pipistrellus species are commonly considered as light-tolerant when studied at a similar spatial scale (Clémentine Azam et al, 2018;Spoelstra et al, 2017;Zeale et al, 2018). Indeed, as light sources used for street lighting massively attract insects (Wakefield et al, 2016),…”

“…Linear landscape elements such as hedgerows and rivers play an essential role for bats commuting between roosts and foraging patches (Akasaka et al, 2012;Lacoeuilhe et al, 2016;Pinaud et al, 2018;Smith and Racey, 2008). Such landscape elements also provide dark corridors in dimly lighted situations (full moon or distant lighting) (Ancillotto et al, 2019;Zeale et al, 2018) and are specifically important in illuminated urban landscape.…”

Low impact of two LED colors on nocturnal insect abundance and bat activity in a peri-urban environment

“…Bats profited from insects at street lights (Table 6, positive correlation between bat passes and insect biomass). The dominating Pipistrellus pipistrellus, is a synanthropic species that is least disturbed by light (Spoelstra et al 2017;Zeale et al 2018). Selective filtering of bat species by ALAN has also been observed by Haddock et al (2019), indicating that clutter adapted species are most intolerant to ALAN (Spoelstra et al 2017).…”

Threat analysis of modelled potential migratory routes for Miniopterus natalensis in South Africa

“…Some notable threats faced by migrating bats in urbanising landscapes include barotrauma-linked mortality (lung damage due to sudden air pressure changes) due to wind turbines (Baerwald et al 2008), vehicular collisions with fast-moving traffic (Myczko et al 2017) and disruption of movement/ migratory paths by artificial lighting (Hale et al 2015;Zeale et al 2018). Another threat to bats is the increased use of agrochemicals in farming practices, either through direct poisoning, or accumulation of organochlorine in body tissues, especially fat, over extended periods (Allinson et al 2006;McCracken 2011).…”

“…2015; Zeale et al . 2018). Another threat to bats is the increased use of agrochemicals in farming practices, either through direct poisoning, or accumulation of organochlorine in body tissues, especially fat, over extended periods (Allinson et al .…”