The emergence activities of nine cave-roosting bats under different lighting conditions

Artificial light at night has become an emerging environmental pollutant,
posing a serious threat to biodiversity. Cave-roosting animals are
vulnerable to light pollution due to long-term adaptation to nocturnal
niches, and the problem is especially severe in the context of cave
tourism and limestone mining. Mitigating the adverse impacts of artificial
light on cave-dwelling animals presents a challenge. Here, we
aimed to assess the relative contribution of spectral parameters and light
intensity to emergence behavior among nine bat species inhabiting a karst
cave, including Rhinolophus macrotis, Rhinolophus pearsonii,
Rhinolophus rex, Rhinolophus pusillus, Rhinolophus siamensis, Rhinolophus
sinicus, Hipposideros armiger, Myotis davidii, and Miniopterus
fuliginosus. We manipulated light spectra and intensities through
light-emitting diode (LED) lighting and gel filters at the entrance of bat
roost. We monitored nightly passes per species to quantify bat emergence
under the dark control and ten lighting conditions (blue, green, yellow,
red, and white light at high and low intensities) using ultrasonic
recording. Our analyses showed that the number of bat passes tended to be
reduced in the presence of white, green, and yellow light, independent of
light intensity. In contrast, the number of bat passes showed no
pronounced differences under the dark control, blue light, and red light.
The number of bat passes was primarily affected by LED light’s blue
component, red component, peak wavelength, and half-width instead of light
intensity. These results demonstrate that spectral parameters of LED light
can significantly affect emergence behavior of cave-dwelling bats. Our
findings highlight the importance of manipulating light colors to reduce
the negative impacts of light pollution on cave-roosting bats as a
function of their spectral sensitivity. We recommend the use of gel
filters to manage existing artificial lighting systems in underground
habitats exploited by bats.