Exploring auditory thresholds for Reindeer, Rangifer tarandus

Current and proposed human development throughout high northern latitudes must assess and try to mitigate impacts on caribou and reindeer (Rangifer tarandus) herds. Sound created by development can be far-reaching, and determining the potential impacts of noise on wildlife can inform landscape use. To advance our understanding of Rangifer’s potential response to anthropogenic noise, we must first understand what they can hear. Using domestic reindeer from the Large Animal Research Station at the University of Alaska Fairbanks, we performed a Brainstem Auditory Evoked Response to estimate auditory thresholds of the species. We assessed the central auditory response and tested the sensitivity in 6 female reindeer of various ages. Prior to our work, the lowest audible frequency for the species was reported to be 63 Hz in previous studies. We identified an auditory threshold lower limit of 30 Hz in our study subjects and quantified reindeer sensitivity thresholds (dB peSPL) to frequencies ranging from 30 to 16,000 Hz. Our results indicate that anthropogenic sounds previously thought to be beyond the hearing range of Rangifer—such as seismic exploration—are likely to be audible to the species, and therefore have the potential to affect their soundscape. We compared our findings on Rangifer hearing with new measurements of anthropogenic sounds recorded on passive acoustic monitors distributed throughout northern Alaska, as well as biological sounds produced by the Rangifer themselves (e.g., vocalizations and sesamoid clicks produced by the ankles). All classes of anthropogenic sound fall within the threshold range that we identified for Rangifer. Our findings have important implications for the assessment of environmental impacts within Rangifer range and will inform future soundscape ecology research.