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Sierra Nevada Bighorn Sheep Progress Towards Recovery

Sierra Nevada bighorn sheep are an endangered species under Federal law and California law. Of more than 1,370 species listed under the U.S. Endangered Species Act since it was passed in 1973, only 47 species have been de-listed. Of the species that are listed, only about 10% are increasing in numbers. Many species continue to do poorly after they are listed because of habitat destruction or other decimating factors that cannot be reversed readily. There is a real opportunity to recover Sierra bighorn because the habitat is intact and there is broad public and agency support for the effort. Sierra bighorn are the only federal endangered species in Yosemite National Park and Sequoia-Kings Canyon National Parks; these parks are anxious to see this iconic mammal restored as part of the native fauna within their boundaries. Down-listing goals can be met in the next decade if recovery actions are implemented. Reintroductions need to occur in 3 additional herd units but the existing herds that serve as translocation stock must be protected.

Population Growth for Each Herd Unit (Ewes)

In bighorn sheep, the number of adult ewes determines how quickly a population can grow or recover from losses. Because of this, the health of a population is often gauged by the number of ewes present. This graph shows population trajectories for adult and yearling females from 1999-2012 based on a combination of population estimates (marked resight and minimum count) for 6 herds in the Sierra with annual population data.

SNBS Herd Unit Size Ewes

Numerical Recovery Goals

The population goal for downlisting to threatened status is 305 females (>1 year).

SNBS Recovery Units and Herd Units



The population must be distributed among 12 of 16 herd units within the 4 recovery units. For delisting the required number of bighorn sheep must persist for a minimum of 7 years without management intervention. Currently, 9 of the 12 required units have bighorn sheep, as does 1 of the non-required herd units and 223 females were observed in 2011 of the 305 required (70% of goal).

SNBS Recovery Units and Population Estimates



The numerical and herd unit / recovery unit occupation is tabularly summarized below. Achieving final recovery goals will require a number of translocations, currently planned at 125 ewes. These ewes will likely be supplied by the Mt. Langley, Mt. Baxter, Sawmill Canyon and Wheeler Ridge herds. Therefore, surplus animals must be available for removal from these herds.

Recovery Unit Herd Unit Recovery Plan Downlisting /
Delisting Criteria
Recovery Unit #Ewes		 Current Population
(2013)
Ewes > 1 yr		 Plan to Achieve
Numerical Goals
Kern Laurel Creek* 50 0 Translocation
Big Arroyo * 0 Translocation
Southern Olancha Peak* 155 10 Translocation
Mt. Langley** 53 Natural growth
Mt. Willamson** 12 Natural growth
Bubbs Creek 9 Natural growth
Mt. Baxter** 38 Natural growth
Sawmill Canyon** 45 Natural growth
Taboose Creek*** 0 Natural colonization
Coyote Ridge 2 Natural growth
Central Wheeler Ridge** 50 40 Natural growth
Convict Creek** 5 Translocation
Northern Mt. Gibbs** 50 7 Natural growth
Mt. Warren** 14 Natural growth
Green Creek 0  
Twin Lakes 0  
Key
     *     -  Required, translocation planned
     **     -  Required, currently occupied
     ***     -  Required, natural colonization