Peninsular Range Bighorn Sheep: 

Habitat Under Attack

By Zac Slavich

Description

Bighorn sheep (Ovis Canadensis) is a species of sheep native to North America. They have ancient roots in Northern America, crossing the Bering land bridge, which existed from 1,000,000 to 10,000 years ago. Bighorns are named for their large horns that can weigh up to 30 pounds. Their coats range in color from light brown to dark brown, with white coloration on their rump and the back of all four of their legs. Males will typically weigh 127-316 lb., measure 36-41 in tall at the shoulder, and 69-79 in long from nose to tail. Females will weigh 75-188 lb., 30-36 in tall, and 54-67 in long. Rocky Mountain Bighorns will be larger than the typical ranges given, weighing up to 500 lb. The Peninsular Range sheep that we will be discussing are on the lower range of the spectrum weighing around 200 lb. 

Comparison of a young ram (below) and a ewe (above)

Habitat
The Peninsular Bighorn Sheep is restricted to the east facing, lower elevation slopes (below 1,400 meters) of the Peninsular Ranges along the northwestern edges of the Sonoran Desert. They require open terrain with good visibility to be able to spot predators at a distance since bighorn sheep rely primarily on their sight. Within their hot, arid habitat, the availability of water is crucial along with forage resources. 

Figure 1: Peninsular Range Bighorns are classified as
O.c. cremnobates

Limiting Factors and Imperilment
The limiting factors of Bighorn Sheep vary with each ewe group. These factors include predation, urban related sources of mortality, low rates of lamb recruitment, disease, habitat loss, and human related disturbance. Their habitat has been fragmented and degraded by the development of highways and other impassible human obstructions. The affects of this have magnified by the the introduction of domesticated animals in or around their habitat. Domesticated animals carry transmittable diseases that are easily passed to bighorns impacting their population negatively. The stress put on them and the fact that their habitats have been isolated has lead to low reproduction rates in the population. Due to these factors the population of the bighorn sheep that inhabit the Peninsular Ranges is critically low, leading to their classification as an endangered species on May 18,1998. During that time their population consisted of 334 animals, distributed in 8 known ewe groups. As of 2010 the population of the Peninsular Range Bighorn had grown to 955 individuals.
Recovery Plan and Criterion

         In response to the critically low population of sheep, scientists have developed 2 criterion that need to be met in order for the species to be down listed from an endangered too a threatened status. First, there must be at least 25 ewes must be present in each of the 9 regions of the Peninsular Ranges for 6 consecutive years (1 bighorn generation). The 9 regions include the: San Jacinto Mountains, Santa Rosa Mountains (North and South of Highway 74, South of Martinez Canyon), Coyote Canyon, North and South San Ysidro Mountains, Vallecito Mountains, and Carrizo Canyon/Tierra Blanca Mountains/Coyote Mountains Area. The second criterion is an improvement of the regulatory mechanisms and land management commitments that have been established to provide better long-term protection of the Peninsular Range Bighorn Sheep. 
          Delisting is the complete removal of the Peninsular Range Bighorn from the endangered and threatened species list. The delisting criteria is essentially the same in the first criterion except there must be at least 25 ewes for 12 consecutive years (2 generations). For the other two criterion required for delisting, a range wide population of 750 individuals must exist for 12 consecutive years, and long-term regulatory mechanisms must be maintained to ensure the protection of the species. Scientists have estimated that this plan will take several decades to take effect. The plan is still in its down listing phase and the Peninsular Bighorn is still classified as endangered. 

The recovery plan covers both short term and long-term strategies. In terms of short-term activities, improving adult survivorship of the population seems most beneficial. Over the long term, primary actions should be focused on conservation of the bighorn sheep’s habitat. These goals will be accomplished by effective management of the species and conserved land upon which they rely. The prevention of habitat fragmentation caused by urban disturbances is key to the survival of ewe groups and adequate buffer space must be provided in order prevent human influences on the population of bighorn sheep. To lessen the effects of habitat fragmentation, land bridges should be established to allow populations of bighorns to cross over or under man made obstructions. Implemented buffer space will also prevent livestock interaction with the rams limiting the amount of diseases they are exposed to.

Figure 2: Steady population growth means an effective
recovery plan

What Can You Do?
The recovery plan, in this instance, is mostly reliant on the management efforts of government organizations such as the Bureau of Land Management and U.S. Forest Service. Because of this, we might ask ourselves, what can we do to help the recovery of the bighorn sheep of the Peninsular Ranges? The first answer is simple and should be applied to all wildlife habitats. Be mindful of your impact on the environment. That means, if you ever find yourself within the habitat of the Peninsular Range Bighorn Sheep, do your best to minimize the impact on the ecosystem. Pick up your trash and the trash of others and be careful with fire as it is one of the main causes of habitat destruction. Essentially do everything you can to prevent a loss of ecosystem not only for the bighorn sheep of the Peninsular Range but for wildlife as a whole. If you still feel the need to do more to help the bighorn sheep of the Peninsular Range, you can donate to the Defenders of Wildlife who use some of these funds to assist in preservation. The link is listed below.    
http://www.defenders.org/bighorn-sheep/basic-facts

For more information take a look at this website:

https://www.dfg.ca.gov/wildlife/Bighorn/Desert/Peninsular/Conservation.html

Works Cited

Rubin, Esther. "Recovery Plan for Bighorn Sheep in the Peninsular Ranges, California." (n.d.): n. pag. U.S. Fish and Wildlife Service. Web. 25 Nov. 2015.

"Bighorn Sheep." Wikipedia. Wikimedia Foundation, n.d. Web. 28 Nov. 2015.

"Biogeography of Bighorn Sheep." Biogeography of Bighorn Sheep. San Francisco State University, 9 Dec. 2002. Web. 28 Nov. 2015.

"Peninsular Desert Bighorn Sheep Conservation." California Department of Fish and Wildlife. California Department of Fish and Wildlife, n.d. Web. 28 Nov. 2015.