If you’ve ever seen a Sierra Nevada bighorn sheep in the wild, count yourself among the lucky ones. They are elusive, they are rare, they inhabit the most remote and treacherous terrain of the mountain range. And, since January 2000, they have been officially endangered.
But state and federal wildlife managers aren’t going to let this genetically distinct wild sheep population die out without an all-out effort to save them. The plight of these majestic, incredibly agile mammals has been noticed, from state lawmakers to biologists to philanthropists.
In effect since 2007 is the “Recovery Plan for Sierra Nevada Bighorn Sheep,” which provides goals and actions to systematically save the precarious population of this unique variant of bighorn sheep that consider the Sierra Nevada their home on the range.
Last month, from March 19 to 22, an unprecedented event occurred in Sequoia National Park that marked a major milestone in the ongoing bighorn sheep recovery effort. Fourteen sheep — 10 ewes and four rams — were moved from wilderness areas in Inyo National Forest and transported to the Big Arroyo region in Sequoia National Park, located about eight air miles east of Mineral King (but 25 or so hiking miles). The area is dominated by the Kaweah Peaks Ridge escarpment and bordered by the Great Western Divide on three sides and the Kern River to the east.
This massive effort included biologists and veterinarians from the California Department of Fish and Wildlife with the assistance of wildlife experts from Sequoia and Kings Canyon National Parks, Inyo National Forest, and the U.S. Fish and Wildlife Service.
Each of the 14 animals was fitted with a radio collar and GPS tracker, so their movements will now be monitored and any mortality investigated. This technology will assist researchers in determining how effective this current translocation project is as well as provide information to assist with the future establishment of two additional herds that will require more sheep be relocated.
There are currently 11 herds of Sierra Nevada bighorn sheep occupying the Sierra crest from Yosemite to Lone Pine, preferring an elevation range of 10,000 to 14,000 feet. This newest group occupies habitat that is the farthest south and west.
Danny Gammons, a wildlife biologist with Sequoia and Kings Canyon National Parks, is front and center in the Sierra Nevada bighorn sheep recovery efforts. Here he describes the complicated and fragile process of how bighorn sheep are reintroduced to their historic range:
How are the sheep selected as the ones to make the move?
The California Department of Fish and Wildlife developed a translocation plan in February 2013. Sheep are selected based on (1) whether the source herd can support removals of ewes (i.e., most animals come from large herds rather than small herds, which minimizes negative impacts to source herds), and (2) genetic diversity (i.e., animals that have been captured previously and are known to have a diverse genetic profile have a higher priority for selection, which promotes genetic diversity and minimizes the risk of inbreeding in the newly created herds). So while most animals will come from large herds, a small number may come from the smaller herds to maximize genetic diversity.
In the recent creation of the Big Arroyo herd, all 10 ewes and one ram came from the Wheeler Ridge herd, northwest of Bishop; and three rams came from the contiguous Sawmill/Baxter herds, west of Lone Pine.
Are any of the ewes pregnant?
Nine of the 10 ewes were pregnant, which was determined using ultrasound.
How are they tranquilized?
There was no chemical immobilization involved. While it may seem counter-intuitive, research has demonstrated that mechanical capture, such as what was used for this project, is superior in terms of reducing animal stress and risk of injury or mortality.
During transport via helicopter, animals were blindfolded and their front and back legs were hobbled or temporarily tethered together to restrict movement. Then, they were placed into specially designed bags in which their legs protruded into the air.
This reduces their instinctual response to kick and helps minimize stress. The blindfold further achieves the effect of calming them and reducing stress.
How are the sheep moved via helicopter?
Animals were transported from their capture site to the base camp (where processing, such as disease samples and placement of radio-collars occurred) via long-line. Depending on the circumstances of the capture (i.e., the proximity of different capture locations) and the combined weight of the animals, anywhere from one to three could be transported on a single line.
After processing at the base camp, animals were placed into custom-made aluminum boxes in the bed of pickup trucks for transport to the release-site staging area along Horseshoe Meadow Road [on the Sierra’s east side near Big Whitney Meadow]. Multiple ewes can be placed in a single box, while rams must be transported individually.
During transport in the boxes, the blindfolds and hobbles/tethers were removed. Once at the release-site staging area, a helicopter picked up the boxes (again with a long-line) and transported them into the Big Arroyo area. Multiple trips were required, but not 14 trips, of course, because multiple ewes could be transported simultaneously.
What are the sheep’s reactions when they wake up in totally new surroundings?
Initially, when the boxes were opened, they seemed to have little reaction. However, after a few seconds, they immediately ran away and headed for higher elevation.
Are there biologists on the ground monitoring this?
Most of the monitoring will be conducted remotely by CDFW through the use of GPS collars, which are programmed to record animal locations every four hours. However, annual on-the-ground monitoring will occur as well to (1) conduct visual counts of the population as new animals are added through recruitment, and (2) to investigate the causes of any mortalities.
Has translocation been implemented before in Sequoia-Kings Canyon?
Between 1979 and 1988, animals were translocated from the Mt. Baxter and Sawmill Canyon herds to establish the Wheeler Ridge and Mount Langley herds, both of which use Sequoia and Kings Canyon National Parks. Interestingly, the Mount Langley herd, re-created through the use of translocations, is currently the largest herd in the Sierra, with more than 50 ewes present as of 2013.
What was the lowest number of bighorn sheep in the Sierra?
In 1995, there were just over 100 bighorn, making them one of the rarest large mammals in North America.
What are their numbers presently? Over 500.
What was the cause of the decline?
The causes of an initial decline in the mid-1880s following settlement from probably more than 1,000 animals distributed from Sonora Pass to Olancha Peak are unclear, but market hunting in mining towns may have played a role and almost certainly die-offs from pneumonia contracted from domestic sheep was important.
By the 1970s, only three herds remained (Mt. Baxter, Sawmill, and Mt. Williamson), comprising about 250 animals. From 1979 to 1988, 103 individuals were translocated from Mt. Baxter and Sawmill to establish the Wheeler Ridge, Mount Langley, and Lee Vining (near Yosemite) herds, and the population increased to about 300.
However, also during the 1980s, bighorn sheep began avoiding their winter ranges, which caused heavy mortality because they stayed at high elevations where they died in avalanches or experienced poor nutrition, which led to reduced lambing and lamb survival. The population began a precipitous decline.
Multiple explanations for this range abandonment were sought, and the only one that was plausible was that bighorn were avoiding mountain lions, their primary predator, which were at the time associated with a high density of mule deer on the winter ranges. By 1995, only 100 animals remained.
In 1999, an emergency listing under the Endangered Species Act was made, and the recovery program began targeted predator management, conducted several population augmentations (i.e., translocating animals between existing herds), worked with the U.S. Forest Service and Bureau of Land Management to reduce the proximity of domestic sheep-grazing allotments, and enhanced habitat quality in two areas by conducting prescribed burns. (All of these actions occurred outside of the national parks.)
Bighorn have since resumed use of their winter range, and the population has responded positively.
What are the sheep’s predators today?
Coyotes, bobcats, or mountain lions can prey on lambs. Mountain lions are generally the only species that will prey upon adults.
Are they facing any human-caused risks presently?
It depends on your perspective. The human-caused risks that caused the bighorn population to initially become endangered have either been completely eliminated (i.e., market hunting) or largely mitigated (i.e., risk of disease from domestic sheep).
From that standpoint, human-caused risks might be considered unimportant, and the remaining risks are really just naturally occurring phenomena, such as random variation in population characteristics like the sex ratio, loss of genetic variability, or vulnerability to stochastic environmental events such as severe winters or vulnerability to predation.
These natural phenomena do not matter to large populations, but they can be catastrophic to small ones, like Sierra bighorn. So while there may not be many direct human-caused threats today, the initial cause of a small population size, which is in itself the primary modern threat, was certainly caused by human-activities.
When is it estimated that additional herds will be translocated?
There are two additional herds that require occupancy under the Recovery Plan: Taboose Creek and Laurel Creek.
Translocation of bighorn sheep into Taboose Creek may not be necessary because it appears it will be naturally colonized by animals from the nearby Sawmill Canyon herd. Taboose Creek currently has a few rams in it and there have been occasional movements of ewes into the area.
Occupation of the Laurel Creek unit will require translocation however. There is no predetermined schedule of when this will begin, but within the next three to five years seems likely.