Sierra Nevada Bighorn Sheep by Vanessa Kao

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Sierra Nevada Bighorn Sheep
By: Vanessa Kao
(image links at the end of the blog)

1. Description and Ecology of Organism
The survival of the Sierra Nevada Bighorn Sheep includes two characteristics: their agility on precipitous rocky slopes which is the primary means of evading predators, and their keen eyesight which is the primary means of detecting predators. 

The optimal habitat is visually open with steep and rocky slopes. They avoid thick brush and forests, and breeding season occurs during late fall and early winter on high elevations. They tend to live in groups, which helps when they go to places with greater risks of predation, such as low elevation ranges in the Sierra Nevada.

Bighorn sheep are herbivores flexible in food consumption and are flexible in feeding habitats utilized. They have short legs and a stocky build, typically 5 feet in length and 2-4 feet tall. The adult male (ram) weighs 120-200 pounds, while the female (ewe) weighs 100-155 pounds. Rams can live 10-12 years, while Ewes can live 12-20 years.

 Sierra Nevada Bighorn Sheep have large curled brown horns that continue to grow throughout their lives. Coat colors of these sheep can range from dark brown to almost white.

2. Geographic and Population Changes



Bighorn sheep were distributed along the crest of the Sierra Nevada in the north to south.
Before European settlement, there was an estimate of more than 1,000 sheep. That number deteriorated in the 19th to 20th centuries mainly because of diseases, competition, and market hunting.

 By late 1970s, there were only two geographic areas with bighorn (near Mt. Williamson and Mr. Baxter). There was a combined population of 250. Another major decline in population happened in the 1990s where only 100 bighorn sheep remained.



3. Listing Date and Type of Listing
On January 3, 2000, the Sierra Nevada Bighorn Sheep was listed as an endangered species after an emergency listing on April 20, 1999.

 4. Cause of Listing and Main Threats to its Existence

The Sierra Nevada bighorn sheep population was declining due to the transfer of virulent diseases from domestic sheep. Pneumonia is the most significant disease threat.


Mountain lion predation of bighorn sheep on winter ranges caused damage to the
population number.

 The small population alone made sheep vulnerable to extinction.
5. Description of Recovery Plan
The biggest goal is to protect big sheep habitat: by identifying and acquiring important habitat not in public ownership from willing landowners and to maintain and enhance integrity of bighorn sheep habitat.


In order to increase population growth, their survivorship and reproductive output of bighorn sheep are enhanced. Radio-collaring and careful monitoring of mountain lions near bighorn sheep rangers manages the predators.

During winter, bighorn sheep should be moved to lower elevation to avoid deaths from diseases and avalanches.

To decrease mortality, the probability of bighorn sheep contracting diseases is minimized. Domestic sheep and goats will not be in contact with big horn sheep. An action plan will be developed if there is a pneumonia outbreak.

Big horn sheep have a higher chance of survival by increasing the number of herds.


6. What Can You Do?
To help the Sierra Nevada Bighorn sheep, one can engage in public outreach and sharing of information in order to foster understanding, respect, and concern for the species.


Human activities affect recovery actions, and spreading awareness can favor their recovery.

People can sign up to become a member of the Sierra Nevada Bighorn Sheep Foundation, who's mission is to sustain a committed advocates for the sheep. They can also attend hosted public meetings focused on Sierra Nevada bighorn sheep ecology, management, and threats to raise awareness.

7. Other Resources
To learn more about the rarest mountain sheep in North America, here's a video that gives more detail regarding the Sierra Nevada bighorn sheep when they were released to Yosemite in 2015.

 Sources
http://www.dfg.ca.gov/snbs/SheepFacts.html
http://www.dfg.ca.gov/SNBS/RecoveryHome.html
https://ecos.fws.gov/docs/recovery_plan/080213_1.pdf
https://ecos.fws.gov/ecp0/pub/speciesRecovery.jsp?sort=1
https://www.fws.gov/nevada/protected_species/mammals/species/sn_bighorn_sheep.html
Image links
1)https://upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Sierra_Nevada_bighorn_sheep_herd.jpg/1200px-Sierra_Nevada_bighorn_sheep_herd.jpg
2)https://cdn.thinglink.me/api/image/596062248804286465/1240/10/scaletowidth
3)http://www.dfg.ca.gov/snbs/images/maps/SNBS_herd_units.jpg
4)https://peopledotcom.files.wordpress.com/2016/08/mountain-lion-1024.jpg?w=1024
5)http://www.esasuccess.org/images/graphs/13240.png
6)https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhaxszR29izW0BUdH2Ui5r5KNMDyu853EsFE_URPqxG5FmfDFrnFiAUOMb5sAy_W8O20QGzwG6mSGgEkOluRvtyyxeBgHYPvxq39cG6a0n3skP4ImvbS4ONDdiqvFTk6KVxnTWR8_no5NyN/s1600/000.jpg


Comments

  1. ANovember 15, 2017 at 9:34 AM

    It is interesting how colonization can not only affect humans but animals native to this land as well. This is shown here with the bighorn sheep dying and declining due to the virulent disease spread by domestic sheep and goats. It is cool that you bring up the use of radio collaring to monitor predators like mountain lions getting to close to bighorn sheep, since we recently in class learned in depth about use of tracking of animals.

    ReplyDelete
  2. UnknownNovember 15, 2017 at 4:59 PM

    The tracking process of mountain lions is super cool! I've been to the sierras many times but sadly haven't seen any bighorn sheep, they look like such cool animals! I love all your photos. It is also pretty sad that diseases from domesticated sheep and goats can wipe out the bighorn so swiftly... hopefully the recovery plan will continue to add to the rise in numbers!

    ReplyDelete
  3. DrWildlifeDecember 1, 2017 at 8:57 AM

    It is unfortunate that one of the main threats to this species is a disease from human-domesticated species. Although, their recovery plan seems pretty straight forward and hopefully easy to execute. They are such strong and unique organisms, it would be sad for them to disappear.
    -Michelle Henderson

    ReplyDelete
  4. DrWildlifeDecember 5, 2017 at 9:12 PM

    I like how you brought up the point of using radio collars on the predators of the bighorn sheep, to help keep track of their locations. -Rachel Kenison

    ReplyDelete

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