Estimating propagation and audibility of industrial noise in subnivean polar bear dens

Abstract

Polar bear (Ursus maritimus) maternal dens are ephemeral and difficult to monitor, so predictive models of noise penetration into dens are needed. Noise propagation into artificial snow dens was monitored from 9 sources typical of industrial activities (2 aircraft, 2 over-tundra tracked vehicles, 4 wheeled on-road vehicles, and humans walking) near Milne Point, Alaska. Dens were built in 4 configurations, 2 depths (100 cm, 70 cm) and 2 closure conditions (closed, open) to model variability in den roof thickness and breeding stage (before, after emergence). An existing polar bear audiogram was used to predict detection probabilities. Levels <200 Hz would be heard poorly; after accounting for hearing, aircraft had ≥75% probability of being detected within dens at distances <1600 m, and ground-based sources at distances <800 m. On average, closed dens reduced noise levels by 15 dB (re 20 μPa) relative to open dens, but there was interaction between den closure and depth. Some sources were likely to be detected farther from dens than expected. The results reinforce the importance of maintaining disturbance buffer zones around polar bear dens.