Effects of 2700 K amber LED with a blue cut filter and 4000 K white LED on light-naïve New Zealand long-tailed bats (Chalinolobus tuberculatus)

Abstract Artificial lighting, particularly blue-rich light emitted by white light-emitting diodes (LEDs), can have a greater impact on bat foraging and commuting behaviours than light with reduced blue wavelengths (Spoelstra et al., 2017). We investigated whether blue-filtered, amber LEDs are less aversive to New Zealand long-tailed bats (Chalinolobus tuberculatus). The effects of amber LED (2700 K with a blue cut filter that excludes blue-wavelength light) and white LED (4000 K) lighting were tested on a light-naïve population in the central North Island, New Zealand. Lighting treatments (amber, white, and unlit) were alternated in four-night blocks over six weeks, with lights operating from 19:00–07:00. This schedule ensured that lights were already on an hour before sunset and remained on for an hour after sunrise, creating a gradual rather than abrupt change in lighting conditions. Each site experienced all three treatments at different times to control for temporal effects. Acoustic recordings of bat call sequences were used as a proxy for nightly bat activity. Bat activity was highest on unlit nights, intermediate on amber-lit nights, and lowest on white-lit nights. Activity under amber lighting (mean ± SE: 3.83 ± 0.84 passes/night) was significantly greater than under white lighting (2.67 ± 0.52 passes/night), and activity under dark conditions (6.12 ± 0.64 passes/night) was significantly greater than under both amber and white lighting. This confirms that white light is locally aversive to light-naïve C. tuberculatus, while amber light may be somewhat less disruptive but still not equivalent to darkness. Further investigation of lighting spectra is needed to better balance human lighting needs with the conservation of light-sensitive wildlife such as C. tuberculatus.