Publications:

Literature Review

Additional Information:

U.S. Fish and Wildlife Information

Bighorn Institute

Status of the Science on Bighorn Sheep From BLM

Peninsular bighorn sheep

Ovis canadensis

USFWS: Endangered
CDFG: Threatened; Fully Protected Species

Background

Distribution, Abundance and Trends. The peninsular bighorn sheep is one of two species of bighorn sheep that occurs in the Plan area. The other species of bighorn is the Nelson or Desert bighorn (Ovis canadensis nelsonii) that occurs in the San Bernardino, Little San Bernardino, Eagle, and Orocopia Mountains. The Peninsular bighorn sheep is restricted to the east facing, lower elevation slopes (below 1400 meters) of the Peninsular Ranges in the Sonoran desert life zone. Range wide estimates of abundance for the U.S. population, from the San Jacinto Mountains to the Mexican border, began in the 1970's. The highest population estimate was 1,171 in 1974. Surveys in the 1970's, 1980's, and 1990's indicate that significant declines have occurred in multiple ewe groups. The synergistic effects from habitat loss, disease, human disturbance, and predation are believed to have caused the decline. The 1998 range wide population was estimated to be 334 animals (excluding lambs). Approximately half of these were in the Plan area in four subpopulations, or ewe groups. The ewe groups in the Plan area are the San Jacinto Mountains group, the northern Santa Rosa Mountains (northwest of Highway 74) group, the Deep Canyon group (southeast of Highway 74 to Martinez Canyon), and the southern Santa Rosa Mountains group (south of Martinez Canyon). The first two ewe groups have the smallest populations, estimated at 24 and 18 respectively, excluding lambs. These two groups are especially vulnerable.

Threats and Limiting Factors. The Peninsular bighorn sheep is endangered because of the loss and fragmentation of habitat, disease, and predation. A limiting factor is that the sheep live in a narrow band of habitat in which they must find the resources needed to survive in a harsh desert environment. This band of habitat is at the lower elevations of the Peninsular Ranges and includes canyon bottoms, alluvial fans, and mountain slopes. Within the narrow band of habitat, bighorn sheep need to be able to move daily, seasonally, and annually to make use of the sparse and sometimes sporadically available resources found within their home ranges. Habitat loss is considered to be one of the greatest threats to the species' continued existence. As humans encroach into the habitat, the resources, and the survival potential of a particular ewe group that depends on them, may be eliminated. Habitat loss can impact the sheep's ability to forage, reproduce, find water, avoid predators, and move among important resource areas and between ewe groups. Habitat fragmentation is recognized as a major threat to Peninsular bighorn sheep because of the dual effect of restricting animals to a smaller area and severing connections between ewe groups, thus creating genetic isolation. Roads and human use of an area can create habitat fragmentation. Habitat modification, such as constructing golf courses and residences in bighorn habitat that attract sheep, creates threats in the form collisions with vehicles, poisoning by toxic landscape plants, entanglement in wire fences, harassment by dogs, and exposure to pathogens and chemicals such as herbicides and insecticides. Disease and predation, particularly by mountain lions, are also significant threats.

Special Considerations. The most impacted portions of Peninsular bighorn sheep habitat have been alluvial fans and canyon mouths. Protection of remaining alluvial fans and canyon mouths in the species' habitat is, therefore, of the highest importance. Many actions needed for the recovery of the species are beyond the scope of this Plan; however, the CVMSHCP needs to be consistent with the recovery plan where elements overlap. A public access plan is needed to provide trails use in bighorn sheep habitat that is compatible with bighorn sheep conservation goals and affords a reasonable level of use to the public. This trails plan is currently being developed; a draft of the trails plan is included in the Administrative Review Draft. It will provide options to minimize detrimental impacts to bighorn sheep within essential habitat and may include trail reroutings, limitations on trail use, and seasonal closures for some areas. Absent a workable agreement on trails, it is possible that the bighorn sheep would not be covered under the Plan.