Monitoring soundscapes to investigate interactions between human activities, Sonoran pronghorn, and other wildlife in Organ Pipe Cactus National Monument

Christianson, David; Antaya, Andrew

This Natural Resource funded project was developed to help biologists at Organ Pipe gain insight into how sensitive park wildlife are influenced by human activity. More specifically, we were interested in the impact of cross border activity on the endangered Sonoran pronghorn. To accomplish this, we used a number of acoustical devices and behavioral observations. Organ Pipe biologists teamed with researchers at the University of Arizona and the NPS Natural Sounds and Night Skies Division. A University of Arizona graduate student in the M.S. Wildlife Conservation and Management program was chosen to lead this collaboration. In FY 2016 and 2017 Andrew developed the field methods, conducted field work, and began analysis of field data. During a preliminary trial period, the team deployed nine acoustic units throughout Organ Pipe and a protocol was developed to test for the effects of vehicle noise on pronghorn behavior. We deployed four motion-sensing cameras around a supplemental food and water site for Sonoran pronghorn along with a Larsen-Davis acoustic device and anemometer. We also deployed motion-sensing cameras at 100, 250, and 500 meters from the microphone. With this design we could quantify pronghorn behavior from video captured by the cameras at the site, while sound was recorded simultaneously, in the 30 minute window preceding a vehicles detection at known distances using the road cameras. We measured 26 motorized vehicles disturbances to Sonoran pronghorn from June 2017 through August 2017. We also measured the noise levels of motorized vehicles traveling from a range of distances to understand how motorized vehicle noise propagates across Organ Pipe. Because of logistical and technical difficulties associated with operating a large number of electronic devices in the desert in summer, we successfully captured only five instances of pronghorn-vehicle co-occurrence on both the microphone and cameras. Nevertheless we recorded 2.4 million 1-s (644 hours) measurements of continuous sound equivalents (LAeq) at the site during the study period which included 26 separate incursion by vehicles. We also successfully recorded pronghorn behavior on 15 separate days, scoring 783 individual pronghorn behaviors. This data revealed that pronghorn walked and ran more and stood less when a vehicle was approaching the site. Pronghorn also foraged 50% less at the feed trough and were five times more vigilant when a vehicle approached the site. The Larsen-Davis microphone measured significantly greater sound pressure from an approaching vehicle out to 250 m, but not at 500m. Most the sound measured at the site was associated with wind which followed a predictable 24-hr cycle peaking in mid-afternoon. Consequently, the microphone could only reliably detect vehicle noise a 2-3 minutes before a vehicle arrived and perhaps only seconds before or after a vehicle became visually detectable to pronghorn. Because large pronghorn behavioral responses were detected over the 30-min window preceding a vehicles detection on a traffic-camera on the road approaching the site, pronghorn must be either detecting vehicle noise at much greater distances than the Larsen-Davis unit or using other visual clues (e.g., dust columns) to detect and respond to approaching vehicles.

Monitoring soundscapes to investigate interactions between human activities, Sonoran pronghorn, and other wildlife in Organ Pipe Cactus National Monument

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