Big Horns Big Problem

(Ed Prescott 07)

   A Brief Description and Summarized Recovery Plan of the Sierra Nevada Big Horn Sheep 

created by: Jonah Levis

           The Sierra Nevada Big Horn Sheep are a distinct subspecies of the California Big Horn Sheep. Their color ranges from dark brown to white, depending on the time of year. Their short legs restrict them from traveling long distances, but their stocky, muscular build gives them the ability to climb steep elevations. Their hooves have adhesive soles that grip well as they trek up steep rocky mountains. Females are smaller typically, maxing at 155 pounds, and have smaller horns, while males weigh up to 220 pounds and have larger, magnificent horns. 

<http://www.nrdc.org/wildlife/habitat/esa/images/pix_ca_full02.jpg>

          They spend most of their time in open habitats with steep, rocky terrain at elevations up to 13,000 feet. They rely on their keen eyesight to detect predators from long distances, giving them time to climb to safety. They feed on various types of vegetation, which, in order to access, sometimes requires Sierra Nevada Big Horns to descend as low 4000 feet to potentially more dangerous areas where predator detection is more difficult. However, when herds become large in size, about 8 or more, more eyes monitor predators which allows herds to access more feeding areas, and as a result, increases reproduction rates. 

         Female and male Big Horns usually live in separate groups, but meet up during mating season in fall. Big horns occupy large amounts of land which creates “geographically distinct metapopulations” (Schwartz 1986), which means multiple smaller herds together make up a population of one larger geographic range. Inbreeding between the same male and female groups generates low genetic variability, and furthermore, makes many Big Horns susceptible to disease; However, “A small amount of genetic exchange among herds via movements by males can counteract inbreeding” (Schwartz 1986). 

(Mandy Watson)

         Disease and Predation are responsible for low Big Horn population, and consequently, their listing as endangered. Early on, humans hunted Big Horns to low numbers, and now mountain lions are their main threat. The other major threat to Big Horn population is disease, in particular, Pneumonia. By January of 2000 only about 100 Big Horns remained. Their population decrease had gotten some attention prior to 2000, however. In 1878 State legislation implemented temporary hunting restrictions, and in 1883 protection became permanent. Nonetheless, population continued to decline. By 1984 Big Horns were listed threatened under the Endangered Species Act (ESA), and on January 3rd, 2000 they were finally determined endangered by the U.S. Fish and Wildlife Service (USFWS). 

         On the recovery priority scale from 1-18, 1 being highest priority, Sierra Nevada Big Horns are ranked at a 3. Immediate actions for recovery include protecting current herds by monitoring predators and promoting population growth. Biologists must promote growth by joining small groups into big groups which will allow Big Horns to feed in more areas because more group members means higher awareness to the presence of predators. Big Horns should be isolated from domestic goats and sheep to prevent cross breeding as well. Biologists must also take action to prevent inbreeding and promote genetic variation. The estimated total cost of this recovery plan implemented over a 20 year span is $21,730,000. If recovery unfolds as planned, workers estimate the species' down listing (going from endangered to threatened) by 2017, and de-listing (becoming a completely independent species) by 2027. Today about 500 Big Horn Sheep inhabit the Sierra Nevada's; recovery is going in the right direction. 

see recovery in action: https://www.youtube.com/watch?v=5KOMCxxTL6U