Sierra Nevada bighorn sheep 

(Ovis canadensis sierrae)

Ecology

Sierra Nevada bighorn sheep are hooved, herbivorous, mammals native to the Sierra Nevada mountain ridge. This species is listed on the emergency endangered list. Big horn sheep rely on these large rocky ledges to flee and climb away from predators. They also heavily rely on visibility in the surrounding environment to evade potential predators, and often live in areas with low and sparse brush. Big horn sheep live in groups as a protective measure for survival. Large groups of sheep provide more eyes and ears, allowing members to spend less time surveying for predators and more time feeding.

These mammals possess the ability to digest a myriad of plants. Bighorn sheep are known to alter their diets based on what provides the best nutrition at the time. Surface water, although important in many desert ranges, is rarely utilized by bighorn sheep. Instead, bighorn sheep in the Sierra Nevada obtain needed moisture from forage or occasional consumption of snow. 

Listing Date and Type

On April 20, 1999 the Sierra Nevada Bighorn Sheep was listed as an endangered species, an upgrade from the 1984 listing status of threatened. During the time of listing species was put under and emergency status with a call for immediate action.

Geographic and Population Changes

Map of the remaining essential herds of Sierra Nevada Bighorn Sheep

As the species lives in the central California mountain range near the the Nevada border, away from large urban centers, its habitat has remained relatively unchanged. Loss of habitat was not a reason for listing the species as the historic range of Sierra Nevada Bighorn Sheep remains essentially intact; it is neither fragmented nor degraded. 

At the time of its listing, the Sierra Nevada bighorn sheep population was very small, with only about 125 adults among five geographic areas with little probability of interchange among those areas. Since 1999, the number of individual sheep in each herd has steadily increased, however this increase has not been enough to downlist the species. This is due to multiple requirements, one of which requires a minimum total of 305 females.

Cause of Listing and Main Threats

Mountain lion predation of bighorn sheep has accounted for the majority of documented mortalities since the late 1970s. The potential for the transfer of virulent disease organisms from domestic sheep to bighorn sheep in the Sierra Nevada was a key factor in listing the Sierra Nevada bighorn sheep. Introduction of domestic sheep in surrounding areas brought new diseases to the habitats of big horn sheep and wiped out a large percentage of the existing population. Pneumonia in combination with other pathogens, is the most significant disease threat for bighorn sheep. While unregulated hunting may have played a role in early population declines, there is no evidence that commercial, recreational, scientific, or educational activities currently are significant threats to the remaining population. 

Recovery

Controlling the mortality rate of the species and increasing survival and reproductive rates is the main goal to strengthen and downlist the species. The protection and enhancement of existing herds to maximize population growth is the first step. Predator management and changes in domestic sheep grazing practices (to prevent contact) are key aspects of the recovery strategy. During 1982 and 1988 to 1990, four mountain lions that preyed on bighorn sheep were removed to help protect sheep herds. A translocation program has been planned that will require one or more sources of Sierra Nevada bighorn sheep with known bacterial and viral histories. Identifying and developing those sources from the current limited herds is one of the greatest challenges to the recovery of this subspecies. The rate of recovery will, in part, be tied to the number of herds capable of producing bighorn sheep for translocation. 

Graph of herd size 1999-2013

Main strategies of recovery include:

• Identify and acquire important habitat not in public ownership from willing landowners.
• Maintain and/or enhance integrity of bighorn sheep habitat.
• Increase population growth by enhancing survivorship and reproductive output of bighorn sheep.
• Prepare and implement a management plan to temporarily protect Sierra Nevada bighorn sheep herds from predation losses, where needed, until viable herd sizes are reached.
• Prevent contact between bighorn sheep and domestic sheep or goats.
• Develop sources of translocation stock.
• Manage potential predation.

What can you do?

The estimated cost over a 20 year timeframe is $21,730,000 to successful restore these herds to a self sustaining species. The Sierra Nevada Bighorn Sheep Foundation was created to help educate, advocate, and conduct research for the species. Donating and becoming a member of this foundation can help restore this unique species. http://sierrabighorn.org/donate

The foundation also offers field seminars with the foundations founder who leads an educational excursion into the Sierra Nevada mountains and provides a rare experience to observe the animals in the wild. 

Citizen science is one of the outreach programs for Sierra Nevada Bighorn Sheep. This program invited citizens who see signs of sheep or observe them in the wild to send any information they have observed or collected to send in for analysis. Location and number are the most important data to collect upon contact as these can help researchers track the movements of herds. all information can be sent to the California Department of Fish and Wildlife at asksnbs@wildlife.ca.gov.

Other Resource

More information about these animals can be found the following websites:

US Fish and Wildlife Service 

https://ecos.fws.gov/docs/recovery_plan/080213_1.pdf

Sierra Nevada Bighorn Sheep Foundation

http://sierrabighorn.org/

California Department of Fish and Wildlife

http://www.dfg.ca.gov/SNBS/

Center For Biological Diversity

http://www.biologicaldiversity.org/species/mammals/Sierra_Nevada_bighorn_sheep/index.html

Bibliography

California Department of Fish and Wildlife. Sierra Nevada Bighorn Sheep. Retrieved November 8, 2017, from http://www.dfg.ca.gov/SNBS/

Service, U. F. (2007, September 2). Recovery Plan for Sierra Nevada Bighorn Sheep . Retrieved November 7, 2017, from https://www.fws.gov/