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.

We manipulated light spectra and intensities through light-emitting diode (LED) lighting and gel filters at the entrance of a karst cave inhabited by nine bat species, including Rhinolophus macrotis, Rhinolophus pearsonii, Rhinolophus rex, Rhinolophus pusillus, Rhinolophus siamensis, Rhinolophus sinicus, Hipposideros armiger, Myotis davidii, and Miniopterus fuliginosus. We recorded echolocation vocalizations per species under the dark control and ten lighting conditions (blue, green, yellow, red, and white light at high and low intensities) via an ultrasonic recording system (UltrasoundGate 116; Avisoft Bioacoustics, Berlin, Germany). Using Avisoft-SASLab Pro (Avisoft Bioacoustics), we inspected bat echolocation vocalizations counted the number of passes per species under each treatment. Spectral parameters and intensity of LED light were measured using an OHSP350 spectrometer (Hangzhou Hopoo Light Color Technology Co., Ltd., China) and an SW582 illuminance meter (Frank Electronics Co., Ltd, China) held horizontally at a height of 1.7 m. The horizontal distance between an experimenter and the lamp was 1 m during luminance measurement. 

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