ESA Assignment
Max Starubinskiy
Bio 227 Spring 2015
Species: Ovis Canadensis sierrae
Organism Ecology
The Sierra Nevada Bighorn Sheep, or Ovis canadensis sierrae, lives in five
distinct subpopulations along the eastern Sierra Nevada mountains, with these
groups adding up to only about 300 individuals total. Both males and females
have permanent horns, with male horns being larger and coiled. Males can get up to one meter tall at the
shoulder, and weigh up to 99 kg compared to the female maximum of 63 kg [LD:1].
They prefer to inhabit alpine and subalpine zones in summer, and use the open
slopes of these rough, rocky and sparsely vegetated mountain highlands. When
winter comes, the Bighorn Sheep migrate to high windswept ridges or else to
lower elevation sagebrush-steppes to avoid the deepest snows and additionally
have more access to vegetation [LD:2].
Species vary and its is shown by the
color variations of the sheeps horns. The colors may range from a white to a
dark brown. When the bighorn sheep gets older their horns become rough and have
scars. Also as the bighorn sheep get older the color of their horns change to a
yellowish brown to dark brown. [LD:1]
They are a diurnal species, grazing and
foraging on their mountain slopes. Their feeding style is opportunistic and
they make do with what is available, searching to find the most nutritious
options within their normal diet of grasses, shoots, twigs, and leaves of trees
and shrubs. Males over 2 years of age live separately from females and younger
males for most of the year outside of the mating season. Breeding season is in
the fall, with a gestational time of about 6 months and most ewes birthing one
lamb at at time. Once a lamb is born,
that ewe will live in solitude for a short while before joining what can be
referred to as a nursery group, which is made up of about 6 ewes and their
lambs. Lambs learn to climb their treacherous terrain quickly, at as young as 2
days old. Lambs reach breeding maturity at around 2 years, and while female lambs
may stay with their mothers indefinitely after maturity, males branch out into
independence as they reach breeding age. These sheep can reach ages of 9 to 11
years, though maximum lifespan of certain rams has been measured at 12 to 14
years [LD:2].
Original Geographic Range
The Bighorn Sheep’s original range
encompassed the eastern slope of the Sierra Nevadas, a portion of the western
slope, and from Sonora Pass to Kern Pass for a total range of about 346 km. The
5 main populations today are distributed across the eastern slope. Though only
five subpopulations remain today, historically there were 20 subpopulations,
with those original 20 dropping to 10 around the year 1900. In the mid 20th
century, that number halved again to the five we see today. In the 1970’s the
count was at a low of only 2 subpopulations in Mount Baxter and Mount
Williamson. Three subpopulations were
reintroduced in 1979 to 1986 from the Mount Baxter population that had
remained. Currently, the subpopulations occur in Lee Vining Canyon, Wheeler
Crest, Mount Baxter, Mount Williamson, and Mount Langley in Mono and Inyo
counties [LD:1]. Though these sheep were established in this range long before
human populations came into the area, the largest population size prior to
human settlement is estimated at over 1000 individuals, compared to 325 today.
These population losses began to occur after humans started immigrating to the
Sierra Nevada range in the mid 1800’s for the California Gold Rush, and ever
since these losses have been reported [RP:12]. Indeed, though there are only
five regions home to Bighorn Sheep populations now, it is likely that
originally there were 16 Sierra Nevada areas that gave home to separate
populations [RP:13]. Though human impact from mining towns have played a huge
role in their loss, a large die off in the 1870’s was attributed to scabies.
More die offs have been linked to pneumonia contracted from domestic sheep
herds, which began to be grazed in the Sierra Nevadas in the 1860’s and
extended into the 1900’s [LD:14].
Principal Threats to Continued Existence
Though these sheep have faced some
hunting, this has not played a large role in population decline. Additionally,
their habitat is in public ownership and largely not subject to resource
exploitation. Consequently, habitat degradation and fragmentation have not
played a significant role in population decline either [RP:21]. Since 1970, a
main source of death and decreased population size to the Bighorn Sheep has
been mountain lion predation (see table 1). In this time period, mountain lion
predation on livestock and pets in the same regions has increased as well
[RP:17]. Indeed, predation has played one of the largest roles in the decline
of this species. Since 1970, this predation has not been properly regulated.
Proposition 117 in California passed in 1990 and effectively ended the
California Department of Fish and Game’s power to remove lions in high risk
Bighorn Sheep habitat areas [RP:22].
Genetic problems have also been a
tremendous issue for the bighorn sheeps. As stated previously there are only 5
subpopulations and it is very likely that they will lose some genetic variability. Its believe that atleast some of the demes
have variation which can be analyzed through DNA and possibly reach our goal.
The goal that is brought before us is to distribute as many different genetic
variations among all species in order to strengthen the chances of survival in
various climates as well as reproduce with one another. [RP:22]
In addition to predation, the Bighorn
Sheep have had such steep declines as a result of disease. Contact with
domestic sheep herds has allowed Bighorn Sheep to contract pneumonia, a disease
sheep are particularly vulnerable to already. Indeed, pneumonia has been known
to be able to extirpate entire sheep populations and cannot be downplayed as a
factor [RP:21]. Despite efforts, the U.S. Forest Service has been unable to
reduce at all contact between Bighorn Sheep and domestic sheep, and thus has
not effectively reduced the transmission risk [RP:22].
ESA Listing
The Sierra Nevada Bighorn Sheep was
proposed as an endangered species in 1999. Following failed attempts at
regulation of faltering populations, the species was emergency listed as
endangered under the ESA in April 20, 1999.This listing has not changed since
its original entrance into the ESA [LD:1].
Recovery Plan
Approved on September 24, 2007, the
Recovery Plan of Ovis canadensis hopes
to achieve population sizes and geographic distribution of Bighorn Sheep in the
Sierra Nevada that ensure long term viability of the population. By achieving
this, the species can then be delisted as endangered [RP:v]. Specific actions
hoped to be taken immediately are protecting the current herds with helping
populations to grow and managing predation, augmenting smaller herds through
translocations, and preventing contact with domestic sheep or goats [RP:vii]. This
plan is estimated to cost $21,730,000 over 20 years, and hoped to reach
downlisting with population growth in 2017 and again in 2027. These dates are estimated with optimal
conditions for population growth [RP:viii]. Recovery potential for this species
is high if immediate action is carried out [RP:32]. In 2000, a temporary order
was issued prohibiting goats and dogs on habitat areas in Inyo National Forest
to minimize transmission of disease, and this temporary order was being
finalized with the publication of the recovery plan [RP:29]. Additional actions taken already have been
reviewing Forest Land and Resource Management Plan to revise terms that allow
detrimental effects to the Bighorn Sheep, such as term grazing permits for
sheep adjacent to habitat areas, prescribed fire, permits for guides and
packers. The prescribed fire is still
being used to decrease mountain lion habitat [RP:29]. The Recovery Plan
outlines that recovery of this species is possible, but only with proper
funding and timely actions taken by agencies involved.
Bibliography
Clark, Jamie Rappaport. ETWP; Emergency Rule to List the Sierra Nevada Distinct Population
Segment of California Bighorn Sheep as Endangered.
Environmental
Conservation Online System. 20 April 1999. http://ecos.fws.gov/docs/federal_register/fr3401.pdf
Sierra Nevada Bighorn Sheep Recovery Team. Final recovery Plan for the Sierra Nevada
Bighorn Sheep. Environmental Conservation Online System. 24 September 2007.
https://www.google.com/search?q=bighorn+sheep&espv=2&biw=1024&bih=494&source=lnms&tbm=isch&sa=X&ei=wIBzVcWxA4m0ogSXp4GoAQ&ved=0CAYQ_AUoAQ#tbm=isch&q=Sierra+Nevada+bighorn+sheep
No comments:
Post a Comment