Soundscapes on the Arctic Coastal Plain: assessing sound disturbance and the auditory sensitivity of caribou (Rangifer tarandus)

Abstract

The Arctic Coastal Plain of Alaska is a region on traditional Inupiat land that supports millions of migratory birds and over half a million caribou (Rangifer tarandus) at the most critical time in their life-histories. They are an important part of seasonal subsistence activities for the surrounding rural Indigenous communities. Therefore, conservation efforts that support this ecosystem also bolster food security in the region. Monitoring this system has increasingly become a necessary and prudent task as the landscape evolves under the pressures of resource extraction and climate change. To date, limited research has been conducted on the sounds present in this environment (i.e., 'soundscape'). Monitoring sounds may help reveal the impact of these stressors and ecosystem-wide changes. There is also a need for researchers to evaluate what portion of the soundscape wildlife can actually hear, so we can better understand how soundscape change might affect them. I conducted two studies that apply soundscape monitoring and acoustic perception to the landscape and wildlife of the Arctic Coastal Plain. First, I evaluated the hearing thresholds of domestic Rangifer tarandus (reindeer) at the Large Animal Research Station at the University of Alaska Fairbanks in 2019 in order to help infer what anthropogenic sounds wild caribou may be sensitive to. Using Brainstem Auditory Evoked Response methods, I found that a caribou's auditory system can detect all forms of anthropogenic sounds that they might encounter on the Arctic Coastal Plain, including low frequency sounds associated with oil and gas exploration. Specifically, I found they can detect sounds as low as 30 Hz with great sensitivity, expanding the known lower limit of their auditory capabilities. This means that caribou may detect sounds of seismic exploration, gravel mine blasting and other anthropogenic sounds associated with resource extraction at a great distance, and may be more affected by these sounds than previously thought. From May through August of 2019, I used acoustic recording units stationed in a random grid across the Arctic Coastal Plain to passively monitor the soundscape study region-wide sound characteristics and their impact on vocal wildlife. Anthropogenic sound (i.e., anthrophony) is a pervasive and often overlooked consequence of land-use change, and something that has been relatively understudied in northern Alaska. For my soundscape research, I modeled the spatial and temporal distribution of anthrophony and bird vocalizations (i.e., biophony) across developed (Oilfields surrounding Prudhoe Bay), and undeveloped (Arctic National Wildlife Refuge) areas of the Arctic Coastal Plain. Hourly detections of anthrophony were not associated strongly with infrastructure but tended to increase as the season went on. Birds were more likely to vocalize in hours when anthrophony was present, and this effect was the strongest in the early season, during migratory bird arrival and breeding. Anthrophony's effect on the soundscape may alter biological cues that vocal and non-vocal migrants use to assess habitat patches, and fitness consequences will vary by species. Further research is needed to assess how bird communities and caribou movement respond to anthrophony.