Do long-tailed bats alter their evening activity in response to aircraft noise?

Abstract

Human-generated noise may alter animal activity patterns and mask vocal signals. We used field-based observations and a playback experiment to investigate whether aircraft activity and noise alter the evening activity of New Zealand long-tailed bats (Chalinolobus tuberculatus) a cryptic threatened species. Low-altitude aircraft activity temporally overlapped bat activity near the runway of an international airport, but was unlikely to mask echolocation pulses as aircraft noise was most intense at ≤ 10 kHz. There was no statistically significant difference in mean bat activity during and after overflights compared with pre-aircraft activity. The experiment revealed that playback stimuli (aircraft passes and two controls: silent tracks and blackbird (Turdus merula) calls) differed in their effect on bat activity at two sites, one with low and one with high aircraft activity. Simulated aircraft noise and silent tracks reduced bat activity when compared with blackbird calls (P < 0.05). Bats may have found it easier to detect observers during the playback of silent tracks (sampling involved walking circuits with hand-held detectors), and may have reduced activity to a perceived threat. This result suggests that broadcasted aircraft noise is no more disturbing than researcher presence during playback trials. Evidence for a site × playback stimuli interaction (P = 0.054) suggests that bats at the site with high aircraft activity may have habituated to aircraft noise. Both correlative and experimental data suggests that aircraft activity and noise may not have major impacts on long-tailed bat activity.