The future of Sierra bighorn sheep
and the role of the Mono Basin
by John Wehausen
He called them "the bravest of all Sierra mountaineers" but John Muir may have observed bighorn sheep only once in all the time he spent in the high Sierra Nevada. His one documented sighting was in the southern Sierra, but Muir's writings nevertheless documented the existence of bighorn in the Mono Basin.
In 1986 bighorn were reintroduced to the Mono Basin from a population further to the south. Now the population in Lee Vining Canyon is the primary hope for the future of Sierra Nevada bighorn.
Impacts on bighorn populations quickly followed California's gold rush days. As a result, the State Legislature enacted laws to conserve bighorn sheep as early as 1873, and gave them full protection in 1878. Historical evidence indicates that bighorn populations were scattered along the crest and east side of the central and southern Sierra from around Sonora Pass to Olancha Peak, and in the Mineral King and Kaweah Peaks area west of the Kern River.
How many there were or what happened to each population that disappeared will never be known. However, it is well established that contact with domestic sheep often results in pneumonia outbreaks that can eliminate entire bighorn populations. Given the high level of domestic sheep grazing that began in the Sierra in the 1860s, and local market hunting, it is a wonder that any native bighorn survived.
About seven Sierra bighorn populations made it to the twentieth century, but by the 1970s, when intensive research began, only two remained. One of them, on Mount Williamson, numbered only 30 sheep and remained at that size up to 1985. The other population (the Mount Baxter herd) ranged from Kearsarge almost to Taboose Pass, and contained 220 sheep in the late 1970s.
The size and productivity of this population allowed the creation of an interagency reintroduction program for Sierra bighorn. Sheep from the Mount Baxter herd were moved over a ten year period to three formerly occupied locations.
This program was initially successful and increased the total bighorn population by about 25%. However, mountain lion predation on bighorn occupying low elevation winter ranges increased dramatically in the 1980s. Each bighorn population responded by abandoning these habitats. This left them wintering high in the mountains in considerable snow, with poor forage resources.
The result has been large population declines, especially during the particularly severe winter of 1995, when many bighorn perished. A careful inventory taken in 1995 and 1996 found only 120 bighorn remaining in the Sierra Nevada, with two populations (Mt. Langley and Mt. Williamson) on the edge of extinction, each with three or fewer ewes left as their reproductive base. The Mount Baxter herd is now only 15% of its former size.
The one hope for recovery lies with the population reintroduced to Lee Vining Canyon in the Mono Basin. Although it suffered a large loss in 1995, 29 survived that winter, and it already showed strong signs of recovery in 1996. Barring an unforeseen catastrophe, it is hoped that this population will serve as a new source of translocation stock in a couple of years.
Recent work on genetics and morphology of bighorn sheep has found Sierra Nevada bighorn to be a notably unique form of bighorn sheep that occurs only in the Sierra Nevada. Consequently, some of the first available sheep may go to a captive facility to help preserve this unique gene pool. Nonetheless, a high priority for use of Lee Vining Canyon stock will be the establishment of other viable populations in the Mono Basin, including Lundy and Bloody canyons. Because the future of Sierra Nevada bighorn hinges so strongly on the Lee Vining Canyon population, Inyo National Forest recently used controlled burning to open up habitat in an attempt to make bighorn less vulnerable to any mountain lions that might happen into the area.
At a time when every possible effort is needed to save Sierra Nevada bighorn, funding is as scarce as the sheep themselves. Consequently, in 1995 the Sierra Nevada Bighorn Sheep Foundation was established as a tax-deductible nonprofit foundation to help assure the future of these unique sheep. If you would like to help, please contact them at P.O. Box 1183, Bishop, CA 93515; (760) 873-4563; or snbsf@telis.org.
John Wehausen is a research associate at White Mountain Research Station in Bishop. He has been investigating various aspects of Sierra bighorn and working for their conservation since 1974. In the late 1970s he initiated the restoration program that brought bighorn back to the Mono Basin.
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