Ethan Rohlf - Sierra Nevada Bighorn Sheep

The Sierra Nevada Bighorn Sheep

(Ovis canadensis sierrae)

A bighorn ewe stands atop a ridge in the Sierra Nevada.

Description and Ecology

The Sierra Nevada bighorn sheep varies in appearance. The color of their coat can range from white to dark brown. Both male and female sheep have permanent horns. These horns vary in color from yellowish-brown to dark brown depending on the age of the sheep. Horns of male sheep curl up, back over the ears, then curve down, forward, and up past the cheeks. In contrast to the massive horns of males, horns of females are much more slender and never form more than half a curl. Adult male sheep stand up to 3 feet tall at the shoulder and weigh up to 220 pounds and females 63 kilograms (140 pounds). Both males and females grow to about 5 feet in length The male sheep(rams) live 10-12 years, while females(ewes) live 12-20 years.

Sierra Nevada bighorn sheep select open habitats that allow them to detect predators and escape up terrain that their pursuer cannot ascend. This terrain is typically rough, rocky and steep. Bighorn sheep can be found as high as 13,120 feet and as low as 4,750 feet. Their biology allows them to be flexible in their food consumption. They eat the grasses, sedges and rushes that grow in their habitat.

Geographic and Population Changes

The Sierra Nevada bighorn sheep used to reside across the Sierra Nevada Mountains from Sonora Pass to Olancha Peak. Today, the northmost herds live near the eastern boundary of Yosemite National Park while the southernmost are on the boundary of Sequoia National Park. In 1995, the bighorn sheep population was at an all-time low with only about 100 sheep remaining. As of today, there are an estimated 325-350 individuals.

Listing Date & Type of Listing

After an emergency listing under the federal Endangered Species Act, the Sierra Nevada Bighorn sheep was added to the list of endangered species on January 3, 2000 after being reclassified from threatened to endangered in California during 1999. Sierra Nevada Bighorn Sheep are listed currently as an endangered species.

Cause of Listing & Main Threats to Continued Existence

Populations of Sierra Nevada bighorn sheep began to decline in the 1870’s after settlers that moved to California for the gold rush brought disease-carrying domestic sheep. The Sierra Nevada bighorns lacked resistance to some of the diseases, which caused them die out. This progressed until the bighorns were locally extinct in the northern Sierras. By 1978 there existed only three herds with 250 total sheep. One reason that the bighorns were affected so severely by the domestic sheep was due to a lack of genetic diversity. Experts fear that another introduction of foreign disease could threaten the bighorn’s recovery. Also, because of already low genetic diversity and barriers that separate herds, conservationists are concerned about ways to increase genetic diversity within the species. Lastly a concern is that the small herds of bighorns are more susceptible to predation.

Description of Recovery Plan

A recovery plan for Sierra Nevada bighorn sheep was created in 2008 with a primary objective to attain sustainable population sizes and geographic diversity of bighorn ship. Conservationists hope to ensure the long-term viability of the species in the Sierra Nevadas. Monitors will protect existing herds by maximizing population growth managing predation and preventing contact between bighorns and domestic sheep. They also hope to reintroduce sheep to certain herds while monitoring and acting (if necessary) to maintain the genetic variation of the herds.

What can you do?

The most important part of helping a species recover is being aware of the factors that affect the recovery of species. To help bighorn sheep you should be aware of your ecological footprint while hiking in the Sierra Nevadas. Leaving trash and plastic or destroying the local flora of the region is harmful to the longevity of the sheep. For ranch owners at the base of the Eastern Sierras in places like Visalia, it is important the you keep your sheep in captivity, as they could transmit harmful disease should they come in contact with the bighorns.

To donate to the Sierra Nevada Bighorn Sheep Foundation - http://sierrabighorn.org/donate

Other Resources

To see more photos of the Sierra Nevada Bighorn Sheep –http://digitalmedia.fws.gov/cdm/search/searchterm/Sierra%20Nevada%20bighorn%20sheep/order/nosort

To learn more about the critical habitat - https://ecos.fws.gov/ecp/report/table/critical-habitat.html

To follow the recovery of the bighorns - https://ecos.fws.gov/docs/recovery_plan/080213_1.pdf

References

Endangered Species Program | Species. www.bing.com/cr?IG=A89934B026414C669A479F92F31A859C&CID=280BE154B34265F81E41EAF8B2ED645A&rd=1&h=7MdsaDd5rVXzySNGlDCVp20ISu1cNkZeBWIbdZBUuE0&v=1&r=https%3a%2f%2fwww.fws.gov%2fendangered%2fspecies%2findex.html&p=DevEx,5108.1.

“Home.” Sierra Nevada Bighorn Sheep Foundation, sierrabighorn.org/.

“Home.” Yosemite Conservancy, www.yosemiteconservancy.org/.

“NPS.gov Homepage (U.S. National Park Service).” National Parks Service, U.S. Department of the Interior, www.nps.gov/.

U.S. Fish and Wildlife Service/Endangered Species, Sarah Leon. “Find Endangered Species.” Official Web page of the U.S. Fish and Wildlife Service, www.fws.gov/endangered/.