EFFECTS OF MOUNTAIN LION PREDATION ON BIGHORN SHEEP IN THE SIERRA-NEVADA AND GRANITE MOUNTAINS OF CALIFORNIA

Mountain lion (Puma concolor) predation caused populations of bighorn sheep (Ovis canadensis) in 2 mountain ranges in California to decline to low densities. In the Granite Mountains in the eastern Mojave Deser t, lion predation reduced the sheep population to 8 ewes and held it a t that level for 3 years, after which the predation abated and the pop ulation has increased at 15%/year for 3 years. Annual survivorship of radiocollared ewes was 62.5% for the first 3 years of study and ail mo rtalities were from lion predation. Mountain lion activity increased i n the southern Sierra Nevada on winter ranges between 1976-1988. Durin g this period, 49 sheep killed by lions were found on the winter range s of the Mount Baxter population. Beginning in 1987, the larger subpop ulation of this herd abandoned use of its low-elevation winter range. Increasing mountain lion predation is the best explanation for these h abitat shifts. The Mount Baxter sheep that remained at high elevations missed a growing season on the winter range, which was reflected in l ower fecal nitrogen levels. The population has declined to <20% of ear lier census totals as a result. Mountain lions effectively halted a pr eviously successful restoration program for bighorn sheep in the Sierr a Nevada and reversed the overall population trend.