Sierra Nevada bighorn sheep - Josh Heath

Sierra Nevada bighorn sheep

(Ovis canadensis sierra)

Image Source: https://www.pinterest.com/pin/AYc

Physical Description

The Sierra Nevada bighorn sheep is a large mammal very similar in appearance to the desert big horn sheep, which is also part of the family Bovidae. As far as physical characteristics go, the Sierra Nevada bighorn’s muzzle, eye patches, stomach, back of legs and behind are all white-colored, while its coat ranges from white to relatively dark-brown. Perhaps the most distinct feature the species boasts are its horns. Both males and females have permanent, symmetrical horns – unlike antlers that shed and grow back. The male sheep have very large, curling horns that often curl past their ears and back past their cheeks as depicted in the image above. These horns can grow to weigh up to thirty pounds, although female sheep rarely have large horns, never forming more than half of a curl. Throughout the lifetime of a sheep, its horns will become dirty and scuffed, as they are used as weapons by males to assert dominance in a banging manner called “rutting”. They can ram into each other as speeds up to 40 miles per hour! The males, called rams, can grow as large as 300 pounds and stand over three feet tall, while females, or ewes, normally grow to about half that size. They also have specialized hooves and tough soles that give them exceptional grip when perusing mountain faces. These sheep are true specimen. 

Life History

Image Source: http://sierrabighorn.org/donate/

Bighorn sheep live in social groups, but rams and ewes only usually meet to mate. The ewes live with the baby lambs, which are typically born in spring, while the rams live in male groups. The males leave the herd when they are between two and four years to join the ongoing bachelor party. To avoid deep snow in the winter months, the sheep either migrate to higher wind-blown ridges or to lower elevation habitats. These sheep are grazers, feeding on grasses during the summer and available shrubs during the winter and spring months. These mammals have a four-part stomach, giving them the ability to eat large amounts of food quickly and digest at a later time in order to hide from predators. The lifespan of a bighorn sheep is around ten years long.

Geographic and Population Changes

Image Source: http://www.dfg.ca.gov/YosemiteProjectMaps.

The Sierra Nevada bighorn sheep is native to the eastern California mountain ranges, specifically in the Tuolumne, Mono, Fresno, Inyo, and Tulare counties. As previously mentioned, they mostly inhabit rocky mountainous areas along the Eastern Sierra Nevada Mountains. Depending on the time of year, their elevation they dwell at is between 4,000 feet and 13,500 feet above sea level (WOW!). Most of the sheep tend to live at higher levels during the summer. Fortunately for the sheep, because much of the Sierra Nevada region they live in is publicly owned land, loss of habitat has not been a limiting factor, unlike many endangered animals today.

Listing Date and Type of Listing

On April 20, 1999, the Sierra Nevada bighorn sheep was initially placed on the U.S. Fish & Wildlife Service’s Endangered Species List during an emergency listing. At the time, it was predicted that the population of bighorns totaled only 122 animals, located in five separate zones, with very little likelihood of exchange between the mammals in those areas. In 2000, Wehausen and Ramey reassigned California populations outside of the Sierra Nevada’s to their own subspecies, and eventually the California bighorn was deemed terminated. In 2007, the final listing name for the Sierra Nevada bighorn sheep was amended to Ovis canadensis sierra. 

Image source: http://www.esasuccess.org

Cause of Listing and Main Threats to Its Continued Existence

The main threats to the Sierra Nevada bighorn include predation, small population size, and disease transmission. The main predator influencing the survival of this species is the mountain lion, which also can live and hunt in the high-elevation of the Eastern Sierra Nevada Mountains. Although predation is not the highest threat to this species, it is still extremely important to note that this species is still harmful to the small populations of sheep. Perhaps the most impactful threat to the bighorn population in the Sierras is the small amount of adult sheep and the distance between herds. With so few sheep in such a large area, many herds do not have the capacity to migrate far enough to breed. With the decline of migration, this species has the potential of decreasing in genetic diversity. The U.S. Fish & Wildlife Service has also noted that disease spread from domestic goats and sheep is also contributing to the decline in population of these sheep. When ranchers moved into the mountain valleys they brought sheep that carried scabies and pneumonia, proving to be fatal diseases for many bighorns.

Description of Recovery Plan

Objective: The main objective of the established recovery plan is to regain population size and geographical volume sufficient enough to ensure long-term populations of bighorn sheep. There is no specific number of sheep suggested to consider the population stable, but conservationists are going to be sure that this species is sufficiently reestablished before delisting it.

Recovery Priority: Recovery precedence for listed species ranges from 1 to 18, with 1 signifying the highest priority for resolution. The U.S. Fish & Wildlife Service has given the Sierra Nevada bighorn sheep a 3 in recovery priority, meaning there is much concern or population growth. A 3 has been assigned mostly because there is a large amount of threat due to the sheep’s fragmented population distribution and small amount of adults.

Image Source: 

https://www.pinterest.com/pin/1681

Delisting Recovery Plan: The official recovery plan was drafted and approved in 2007 and predicts the species be delisted within twenty years (2027), but if unforeseen disasters occur, the recovery could take several decades. At the time this recovery plan was published, conservationists estimated the species totaled approximately 350 adult sheep. The total cost of this recovery plan is estimated to total $21,730,000. The immediate actions taken consist of:

1.       Protecting the remaining herds by

a.       Maximizing population growth

b.      Predator control and management

c.       Fencing and assistance in guided travel to induce interbreeding of herds

2.       Supplementing smaller herds with more species because a larger amount of sheep will result in more migration and more awareness of potential predators.

3.     Segregate and prevent any contact between the Sierra Nevada bighorn sheep and any domestic goats or sheep, regardless of the possibility of carrying disease.

Some future actions that will also occur include:

1.       Augment sheep into struggling herds units that are lacking genetic diversity.

2.       Monitor genetic discrepancy of all other units – take action to maintain diversity to prevent spread of disease. 

                                              What Can YOU Do?

Image Source:

http://www.sierrabighorn.org

Although these bighorn sheep are experiencing a successful recovery plan thus far, they are still endangered and need our help. There are very many options for helping these animals ranging from donating money to foundations like The Sierra Nevada Bighorn Sheep Foundation to physically volunteering to help with the recovery plan. Like myself, most people may not realize that the Sierra Nevada bighorn sheep are endangered, so sharing information on their need for help and funding would spread the awareness. Several conservationist groups have created marketing, t-shirts, posters, and other informational propaganda to raise money and provide awareness to support this recover program as well. If you would like to get involved or learn more about how you can help follow this link http://sierrabighorn.org/donate/. If you would like to be more involved and frequently updated by this club, feel free to follow them on Facebook as well at https://www.facebook.com/SNBSFoundation.

Other resources

If you would like to explore any of the information covered in this blog or explore more about saving this incredible species, feel free to click any of the following links:

https://ecos.fws.gov/ecp0/profile/speciesProfile?spcode=A0DS

https://www.fws.gov/nevada/protected_species/mammals/species/sn_bighorn_sheep.html

https://www.nps.gov/romo/learn/nature/bighorn_sheep.htm

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