Sierra Nevada Bighorn Sheep

Source: http://www.monolake.org/today/wp-content/uploads/2017/02/SNBSF-sheep-1.jpg

Sierra Nevada Bighorn Sheep

Cody Capella - Bio 227, Fall 2017

About the Sierra Nevada Bighorn Sheep

The Sierra Nevada Bighorn Sheep is a relatively large (adult males range from 120-220 pounds, adult females from 100-155 pounds) sheep that inhabits California’s Sierra Nevada Mountain Range, hence their scientific name Ovis canadensis sierrae (“Sheep Facts”). They are close relatives of the other two types of bighorn sheep that share a similar habitat in the United States, the Rocky Mountain bighorn sheep and the Desert bighorn sheep (“Natural History”). As they are genetically different from these other species, however, they are their own distinct subspecies of bighorn sheep (USFWS).

Since they inhabit steep, rocky ranges, they are very agile and have short legs and stocky builds to make them better adapted to navigating in the challenging Sierra terrain; they range in elevation from over 4,000 meters during the summer to in some cases as low as 1,450 meters during the winters (USFWS). They spread out over such a wide range in order to ensure that they get enough food — they are herbivores, but have very flexible diets and will eat whatever is available and most nutritious based on where they are and the season (USFWS).

The Sierra Nevada Bighorn Sheep lives in groups, which affords them protection from predators and allows them to graze more efficiently. They have very sharp eyesight, which is their primary means of detecting predators; they are frequently preyed on when they move to lower elevations during the winter, and especially by mountain lions, which account for the majority of bighorn fatalities (USFWS). Bighorns typically do not move between herds on their own, and males and females live in separate groups, only coming together in late fall to breed; since females typically only give birth to a single young, so their population is especially vulnerable to outside risks like predation and disease as it is still so small in size (USFWS).

Geographic and Population Changes
One of the biggest limitations on the population of Sierra Nevada bighorns are outside factors, especially disease and predation. As mentioned previously, one of their largest predators is the mountain lion, which has kept bighorn population sizes small. They are also extremely susceptible to pneumonia, which is considered the most significant disease for bighorn sheep  and can be contracted from contact with domestic sheep, in addition to other illnesses that negatively impact Sierra Nevada bighorns like scabies (USFWS). Human impacts today on the species are thought to be relatively negligible, though initial hunting when humans first moved into the Sierra Nevadas likely reduced the bighorn population from what it was before human contact.

Historical and current ranges of the
Sierra Nevada Bighorn Sheep.
Source: http://www.dfg.ca.gov/snbs/images/maps/
SNBS_herd_units_and_historical_loc.jpg

Their population prior to settlement is unknown, but it is thought to have been just over a thousand sheep, with losses starting to occur shortly after European immigration to the areas typically inhabited by bighorns in the middle of the nineteenth century, largely thought to be due to diseases brought by the domestic animals of the Europeans (USFWS). More recently, however, the bighorn population has drastically declined, reaching an all-time low of just over 100 sheep in 1995, down from the previous low point of nearly 300 bighorns in 1985. This is largely due to the change in bighorn behavior that occurred around this time in which they stopped descending to lower elevations to spend the winter, likely due to predation by mountain lions (USFWS). Due to harsh winter weather conditions at higher elevations and less abundance of food, bighorn survival took a big hit due to these changes in range behavior and while the population is now growing again, it is still well below its targets for delisting and covers a much smaller range geographically today than it did historically.

Listing Date and Type of Listing

The Sierra Nevada Bighorn Sheep was listed as endangered under the California Endangered Species Act in 1999, and was later listed as endangered by the U.S. Fish and Wildlife Service on January 3, 2000 (USFWS).

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Cause of Listing and Main Threats

Neither the habitat of the Sierra Nevada Bighorn Sheep, which has remained largely undisturbed from its initial condition before settlement, nor overuse by humans have had very important impacts on the bighorn population, so neither of those were considered reasons for listing it as endangered. Its main reasons for listing were the potential for diseases to be transmitted to wild bighorns from domesticated sheep and goats (as bighorns are incredibly susceptible to these diseases), predation from mountain lions in their winter ranges, and the current lack of policies in place that reduce contact between domestic animals and bighorn sheep (USFWS). The incredibly small size of the population was also another incentive to listing them as endangered, as it makes them all the more vulnerable for extinction because of these diseases and predators.

Recovery Plan

As stated in the U.S. Fish and Widlife Service’s Recovery Plan for the Sierra Nevada Bighorn Sheep, the goal is to both recover the population to a size that can sustain itself across most of its historic range while maintaining enough genetic diversity to ensure it stays distinct from other sheep species, as well as put programs in place to protect them to threats that might arise following their delisting.

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In order to be downlisted to threatened, there must be both 305 females over one year old across the range’s four Recovery Units (areas designated to break up the population’s recovery based on geographically distinct regions of their historic range), as well as policies put in place that eliminate contact between domestic sheep and goats and wild bighorns (USFWS). In order to be delisted entirely, the above criteria need to be met, but the required female population must be maintained for at least seven years without human help; bighorns need to be found in at least twelve herds in total across the four Recovery Units; all populations in Recovery Units must be thought to be able to continue supporting themselves without human help; and regulations and land protections must be put in place to protect the species and their summer and winter ranges long-term (USFWS).

The U.S. Fish and Wildlife Service’s Recovery Plan contains eight action items in order to ensure successful recovery of the Sierra Nevada Bighorn Sheep, the first of which is protecting bighorn habitat by both maintaining the habitat that is already owned and protected by the state, as well as attempting to buy up privately-held land that is in the bighorn’s range. The second action item is to increase the population growth of bighorns by ensuring they have a higher chance of surviving overall, as well as a greater chance of reproducing successfully; they plan to achieve this by monitoring and removing predators from bighorn ranges, increasing bighorns’ use of lower-elevation habitat during the winters, and minimizing contact between bighorns and domestic animals so they have a lesser chance of getting sick from diseases. The third goal is to increase the number of herds and sheep overall across the population by relocating bighorns from thriving areas (whether that be in the wild or through a captive breeding program) to those that need to have a herd reestablished. The fourth item is to implement a plan to monitor and maintain the species’ genetic diversity. The fifth goal is to monitor the sheep and their habitat to collect data and look for trends in population size and distribution, their habitat, and the threats to bighorns’ survival. The sixth goal is to research more deeply various aspects of bighorn ecology, behavior, and the effects of their interactions with the environment, predators, and humans, as well as the potential effects that climate change could have on bighorn survival. The seventh item is to engage the public by educating them, conducting a survey of how bighorn habitat is used by people and their attitudes towards Sierra Nevada bighorns, and working to update existing programs as needs change. Lastly, they aim to create an advisory team to coordinate communications and actions between Federal, state, private, and specialist groups that are involved in helping protect bighorns.

Source: https://www.nps.gov/yose/learn/nature/images/ram_SteveYeagerweb.jpg

What You Can Do

While human influence hasn’t had too much of an impact on the recent survival of the Sierra Nevada Bighorn Sheep, that doesn’t mean there’s nothing you can do to help them as a species. One of the action items listed above in the Recovery Plan is public outreach and education, and you as an individual can play a big part in helping to educate people about and advocate for the Sierra Nevada bighorn. If you live in an area close to bighorn habitat, make sure that your friends, neighbors and others in your community know about the bighorn and take active steps to ensure the preservation of their habitat by being mindful of how they use the land if they are in bighorns’ range. If you have domestic animals, take steps to fence or otherwise contain them and prevent contact with wild bighorn to reduce the chance of accidental transmission of disease to wild bighorn sheep.

Several groups also advocate for the preservation of Sierra Nevada Bighorn Sheep, including the Sierra Nevada Bighorn Sheep Foundation (www.sierrabighorn.org) and supporting them either financially or by advocating on their behalf is a great way to help protect this species. The Foundation also has a Citizen Science program which encourages hikers and outdoor enthusiasts to report sightings of bighorns, which helps the foundation monitor bighorns throughout their ranges. If you’d like to get involved, visit their website (linked above). Lastly, another great way to help protect bighorns is to reach out to your local government representative and express your interest in conserving Sierra Nevada bighorns; by encouraging them to support legislation that protects wild places like bighorn habitat, reduces private sales of land in bighorn habitat, or provides more funding for conservation efforts, your voice can have a lasting impact on the long-term survival of Sierra Nevada Bighorn Sheep.

Source: https://www.nps.gov/seki/learn/nature/images/8682115810_7f7b0da5b0_b_1.jpg

Additional Resources

If you’d like to learn more about Sierra Nevada Bighorn Sheep or take steps to get involved with species conservation, take a look at the resources listed below.

Sierra Nevada Bighorn Sheep Foundation
www.sierrabighorn.org

Sierra Nevada Bighorn Sheep in Yosemite National Park
www.nps.gov/yose/learn/nature/sheep.htm

U.S. Fish and Wildlife Service: Sierra Nevada Bighorn Sheep
www.fws.gov/nevada/protected_species/mammals/species/sn_bighorn_sheep.html

California Department of Fish and Wildlife: Sierra Nevada Bighorn Sheep Program
http://www.dfg.ca.gov/SNBS/

Center for Biological Diversity: Sierra Nevada Bighorn Sheep
www.biologicaldiversity.org/species/mammals/Sierra_Nevada_bighorn_sheep/index.html

Works Cited

Cassel, Bonnie. "Sierra Nevada Bighorn Sheep in Yosemite National Park." Yosemite National Park. National Park Service, 3 Aug. 2017. Web.

"Natural History." Sierra Nevada Bighorn Sheep Foundation. Sierra Nevada Bighorn Sheep Foundation, n.d. Web.

"Sierra Nevada Bighorn Sheep Facts." California Department of Fish and Wildlife. California Department of Fish and Wildlife, n.d. Web.

U.S. Fish and Wildlife Service. Recovery Plan for the Sierra Nevada Bighorn Sheep. Sacramento, California, 2007. xiv + 199 pages. Web.