A Historical Review of Sierra Nevada Bighorn and the Road to Recovery

By Tom Batter, Wildlife Investigations Lab Scientific Aid

“Bighorn… are extremely wary and cautious animals…His strength and his self-reliance seem to fit him above all other kinds of game to battle with the elements and with his brute foes; he does not care to have the rough ways of his life made smooth; were his choice free his abode would still be the vast and lonely wilderness in which he is found.”

Theodore Roosevelt, Ch. VII A Trip After Mountain Sheep, Hunting Trips of a Ranchman (1885)

While the future President Roosevelt was referencing bighorn sheep (Ovis canadensis) of the North Dakota badlands, his description can be applied just as aptly to the Sierra Nevada bighorn (O. c. sierrae) of California’s east-central boundary.  The rugged mountain peaks and canyons combined with semi-open forest areas provide ideal habitat for these bighorn.

An alert group of Sierra Nevada bighorn.
Image courtesy of John Wehausen & the US Fish & Wildlife Service

Sierra Nevada bighorn sheep (SNBS) are an endangered genetically distinct subspecies of bighorn. They are only found in the mountain range that provides their common name.  Today, these sheep are on the road to recovery, in part thanks to intense monitoring by the Department of Fish and Game’s Sierra Nevada Bighorn Sheep Program (SNBSP) in conjunction with the Sierra Nevada Bighorn Sheep Foundation.  Led by Dr. Tom Stephenson, the program’s goal is to recover sheep numbers to the point that downlisting, or the ultimate goal, delisting, would be warranted.

Recovery activities center around understanding and managing factors that influence population health and the distribution of these bighorn. Among the factors that could be limiting Sierra Nevada bighorn numbers are disease from domestic sheep, predation, weather events and forest succession, which may limit habitat.

Indeed, the preferred haunt of the bighorn is open habitat adjacent to steep and rocky ground.  They are behaviorally and morphologically suited for such an environment.  Bighorn are equipped with keen binocular vision to detect predators from a great distance. Their short legs, hefty frames and low center of gravity provide agility and tremendous balance.  Their hooves are hard on the outer edges and spongy at the center, a unique adaptation that facilitates exceptional grip on rock.  When danger is perceived, the sheep make the most of their physical abilities by retreating into the nearby cliffs and rock walls where few predators can pursue them.

A home fit for a sheep.
(Photo credit T. Batter)

While it is true bighorn are first-rate predator evaders, they have historically had a harder time avoiding another serious threat: humans.

It was during the mid-1800s that Sierra bighorn sheep numbers began to decline.  Throughout this time California experienced a population boom due to the discovery of gold.  Once the gold rush craze eased up, settlers that remained in the area turned to ranching.  Domestic sheep and cattle began grazing the Sierras, increasing forage competition.  At the beginning of the 20th century, bighorn numbers were down to the thousands.

Domestic sheep graze in the Sierras.
Image courtesy of USDA-Forest Service

Grazing sheep and cattle on western federal lands became the subject of a sizzling congressional debate.  President Roosevelt was neither a fan of forest grazing nor of domestic sheep themselves – he described them as “the most foolish of all tame animals” and referred to flocks as “fleecy idiots.”  A quarrel over sheep grazing created a rift between legendary conservationists John Muir and Gifford Pinchot.  Pinchot assured Muir he was against sheep grazing in forest reserves.  Muir furiously confronted Pinchot over quotes in a Seattle newspaper that suggested otherwise. Disagreement between wool growers and preservationists was high, which ultimately led to grazing regulations and agreements.

While forage competition and over-hunting played a role in bighorn population decline, today one of the most critical threats to Sierra Nevada bighorn recovery is disease transmission from domestic sheep .  Domestic sheep are carriers of pathogens that cause respiratory disease in wild sheep.  While domestic sheep remain unaffected, bighorn that are exposed have no defense against these pathogens and are therefore extremely susceptible to disease and ultimately death.

Recent pneumonia related all-age mortality events have resulted in the deaths of hundreds of bighorn in the Rocky Mountain West. Research implicates a particularly difficult-to-diagnose bacteria,  Mycoplasma ovipneumoniae, in initiating many of these outbreaks.  While Mycoplasma ovipneumoniae is commonly found in healthy domestic sheep, years of extensive testing has demonstrated that this bacteria is absent from Sierra Nevada bighorn herds.  This absence certainly results in healthy bighorn, but it also means that the wild herds will be very susceptible to respiratory disease if they are exposed to the organism.  Once exposed, the typical sheep habit of nose-to-nose greetings can result in the unstoppable transmission of the organism within the herd.  Extensive ram movements can then spread the disease to other populations.  Historically, these disease outbreaks have resulted in initial all-age mortality followed by years of high lamb mortality, both of which will delay or prevent the recovery of the Sierra Nevada bighorn sheep.

By the mid-1990s, an estimated 100 bighorn remained in the Sierra Nevada region.  Such low numbers expedited the process of listing the sheep as endangered; in 2000, the Sierra Nevada bighorn sheep became the first federally endangered species listed in the 21st century.

Bighorn sheep have heavy ridges which run across the horns, formed each winter. It is possible to age a sheep based on the number of deep grooves. This ram I am supporting was about 7 years old and weighed in near 240 lbs! (Photo credit T. Batter)

This is where Dr. Tom Stephenson, SNBS program personnel, and the Wildlife Investigations Lab (WIL) enter the equation.  Once every fall and spring, Sierra Nevada bighorn are captured and fitted with radio and GPS collars.  Sheep are captured from a helicopter using a hand held net gun (services rendered by Leading Edge Aviation).  The captured sheep are hobbled, blindfolded, and securely fastened into a carrier.  The sheep are then airlifted to a base camp and monitored by processing teams where their safety is the top priority.  In base camp, WIL provides essential equipment, expertise and training in wildlife restraint and humane care, as well as veterinary medical care of injuries or medical problems that occur during the capture

WIL veterinarian Dr. Ben Gonzales lends his expertise in monitoring the health of each sheep that is flown in.  Crew members are trained to closely monitor the bighorn and to collect appropriate blood and nasal samples to evaluate population health.  After the team fits the collars and applies an ear tag, the bighorn is then airlifted back to the capture site where it rejoins the flock.  The collared sheep will then begin to accumulate data that is imperative to their recovery success.

The radio and GPS collars are very useful and important tools in the recovery process for these animals.  Movement patterns, habitat use, survival and causes of mortality can all be examined.

Radio and GPS collars are securely fastened on a ram.
(Photo credit T. Batter)

Furthermore, human recreational impact on the bighorns can be assessed, as well as the grazing overlap between bighorn and domestic sheep.  The collected data will allow for science-based management decisions to be made in order to ensure the survival of Sierra Nevada bighorn.  So far, efforts have helped increase Sierra Nevada bighorn numbers to over 400 individuals.

The Leading Edge Aviation crew as they airlift two processed sheep back to their flock. (Photo credit Trista Welsh)

President Roosevelt went on to describe bighorn sheep as having “…no animal in the world his superior in climbing…”  With successful recovery efforts, the SNBS Program and the Sierra Nevada Bighorn Sheep Foundation in partnership with the Wildlife Investigations Laboratory will help guarantee that these rare bighorns remain the ultimate mountain climbers well into the future.

SNBS ewe is collared, tagged, and ready to return! (Photo credit T. Welsh)

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