The Effects of Low-Altitude Aircraft on Mountain Sheep Heart Rate and Behavior

We determined the influence of F-16 aircraft overflights on mountain sheep (Ovis canadensis nelsoni). We created an enclosure and calibrated the area for sound created by F-16 aircraft flying along the ridgeline, approximately 125 m above ground level. In 1990 we placed 12 mountain sheep in a 320-ha enclosure in the Desert National Wildlife Refuge, Nevada. We monitored their behavior for 1 year to ensure they were habituated to the area before they were influenced by the F-16 aircraft. Habitat use and activity of mountain sheep in the enclosure was similar to habitat use and activity of free-ranging mountain sheep. In May 1991 we instrumented 5 mountain sheep with heart-rate monitors and added them to the population. From May 1991 to May 1992 F-16 Aircraft flew over the enclosure during 3 1-month periods. We recorded heart rate and behavior of sheep 15 minutes prior to, during, and after overflights. Heart rate increased above normal in 21 of 149 overflights but returned to normal within 2 minutes. We conclude that when F-15 aircraft flew over the enclosure, the noise levels created did not alter behavior or increase heart rate to the detriment of the population.