Bighorn sheep are descendants of Siberian Snow Sheep that crossed the Bering land bridge to northern Alaska a little more than one million years ago during the Pleistocene Era. The native distribution of bighorn sheep prior to the appearance of Europeans was in the some of more rugged terrain of western North America from the Canadian Rockies south to northern Mexico, including Baja California. This species has diverged into three distinct subspecies: Rocky Mountain bighorn sheep (Ovis canadensis canadensis), desert bighorn sheep (Ovis canadensis nelson), and Sierra Nevada bighorn sheep (Ovis canadensis sierrae).
Sierra Nevada bighorn are found only in their namesake mountain range. Molecular genetic analyses indicate that they diverged from desert bighorn about 300,000 years ago. This means that they have persisted in the Sierra Nevada through three glacial cycles (ice ages). During that time period they have become alpine specialists and consequently share life history characteristics such as lambing period with more northern populations of bighorn sheep. They have been able to persist in this one mountain range through the radical climatic changes associated with glacial cycles because the Sierra Nevada has a large altitudinal gradient and is long with a significant north-south climatic gradient. The result is that there has always been enough suitable habitat for these sheep somewhere in that range during all climatic conditions.
Most recently, prior to the appearance of Europeans and their domestic livestock in the 1800s, Sierra Nevada bighorn utilized habitat along the crest and eastern slopes of the Sierra Nevada from the Sonora Pass region in the central Sierra to the most southern alpine peaks south of Mount Whitney, also occupying the Great Western Divide further west in the Mineral King region in southern Sequoia National Park. At least 1,000 bighorn sheep probably inhabited the region prior to 1850, but early unregulated hunting and the spread of respiratory diseases contracted from domestic sheep ultimately led to the loss of most populations, with a total population of barely more than 100 animals persisting in 1995. In 1999 the Sierra Nevada Bighorn Sheep Foundation and four other non-profit organizations successfully petitioned the U.S. Fish and Wildlife Service to grant these sheep emergency endangered species status, and full federal endangered species protection was attained within a year. Also in 1999, the Sierra Nevada Bighorn Sheep Foundation filed a petition with the state of California that led immediately to endangered status under the California Endangered Species Act.
In recent years Sierra bighorn have been the only federally-listed endangered species in Yosemite, Sequoia, and Kings Canyon National Parks, and the only federally-listed endangered mammal on the Inyo National Forest. John Muir referred to them as “the bravest of all the Sierra mountaineers”. We consider these graceful icons of the most rugged Sierra Nevada wilderness worthy of our protection, respect, and restoration efforts.