Bighorn Sheep Are Helicoptering Their Way Back From the Brink

California Fish and Wildlife is helping endangered bighorn sheep reclaim their old range—by lifting them over the humans and mountain lions.

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Thirteen bighorn sheep, including this female, were released last month in Yosemite National Park, at the northern end of their historic range in the Sierra Nevada. 


In a snow-flecked campground at 10,000 feet, a petite biologist named Alex Few is giving  last-minute instructions to her crew. The sound of the helicopter reaches them before they see it coming in low over the lodgepole pines, bright red against the gray crags of the Sierra Nevada.

“Who are the people drawing blood?” says Few. “Who are the data collectors? Remember: Keep your knees under the sheep’s head.”

Three orange slings dangle from the helicopter on a single line. Each sling contains a Sierra Nevada bighorn sheep.

Three sets of wildlife workers scramble to meet the chopper. A minute later they hurry back through the dust kicked up by the rotors. Each group carries a sheep on a stretcher, its eyes covered by a blindfold and its feet bound together.

The tawny sides of the animals are heaving in the cold, thin air.

The California Department of Fish and Wildlife is trying to help Sierra Nevada bighorn sheep by transporting them into open territory—and it’s working. The population of this endangered subspecies of North American bighorn was down to as few as 100 individuals. Now it has increased to about 600, half its estimated historic level.

Three orange slings dangle from the helicopter on a single line. Each contains a Sierra Nevada bighorn sheep.

The bighorn never occupied a continuous band of the Sierra Nevada. They were concentrated in loosely connected pockets, and over time the connections broke. Hunting and diseases caught from domestic sheep, such as pneumonia and scabies, diminished the herds and isolated them from one another. Predation by mountain lions also took a toll.

California wildlife biologists are aiming to restore robust herds in 12 adjacent chunks of habitat. Instead of using captive-bred animals, it’s extracting wild sheep, mostly pregnant ewes, from healthy herds and using them to start or augment other herds.

The biologists can’t depend on the bighorn to recolonize their former range: The sheep, especially the ewes, don’t like migrating through forest where mountain lions might pounce. They’re creatures of open cliffs and ledges.

“They are so impressive to watch move among the cliffs,” says Tom Stephenson, director of the Fish and Wildlife program.  “They clearly belong in them.”

First, Catch a Bighorn. Then Give It A Physical

To locate a source herd and extract sheep, a helicopter pilot follows signals from their radio collars. As the helicopter swoops, a gunner in the open bay fires a modified shotgun that deploys a net around the sheep. The aircraft lands, and another crewman, the “mugger,” jumps out. He blindfolds and hobbles the sheep and wrestles it into a sling.

The sheep picked up on this day in late March come from 14,000-foot Mt. Langley. They’re headed for a new home in the Cathedral Range in Yosemite National Park. (Read about the sighting of a rare red fox in Yosemite.)

But first they must be examined thoroughly here at the way station the state wildlife biologists have set up at a campground near Lone Pine. About 25 people, including volunteers, work under Few and Stephenson. Stephenson’s clothes are stained brown from years of handling bighorn.

Ewes’ horns have a slight curl and are no more than two feet long—perfect for one person to grab onto while others work on the sheep. First they weigh the animal on a suspension scale—100 pounds is about right for a ewe, but a ram can weigh twice that—unfurl a tape measure along its spine, and count its lower teeth to determine its age.

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Male bighorns—this is another of Yosemite’s new denizens—have far more massive horns than females and can weigh twice as much.


Then they splash water on the sheep’s throat to mat the hair and expose the jugular so they can draw blood. They take nasal swabs and fecal swabs to check for disease and parasites.

The workers do all this with a minimum of talking. Meanwhile a rectal thermometer keeps track of the sheep’s temperature—a proxy for stress.

In spite of all the pushing and probing, the sheep are breathing easier now. Their placidity is remarkable: It seems the wildness drains out of them the moment the blindfolds are put on.

“Of all the animals I’ve dealt with, sheep are the calmest,” says Bud Adams, a wildlife veterinarian who has come from Oregon. “Once they’re caught, they give up.”

When the work is over, the handlers cradle the heads of the sheep on their laps. “We keep the heads up to help them burp.” 
Cody Massing

Stephenson grabs a handful of hair from one ewe’s side and pulls it right out, exposing the skin. The sheep barely flinches. Pressing an ultrasound probe against the bare spot to scan for a fetus, Stephenson explains that a bighorn’s readily detachable hair might be an adaptation to foil a predator—leaving it with a mouthful of wool as the sheep bounds away.      

When the work is done, the handlers cradle the heads of their charges on their laps. The animals look like masked dogs curled up next to their owners. Cody Massing of California Fish and Wildlife explains that as ruminants the sheep must regurgitate their food. “We keep the heads up to help them burp,” he says.

Next Stop, Yosemite      

But lift a bighorn onto the bed of a pickup, remove its blindfold and hobble under a tarp, and it’s a wild animal once more. Then you need as many people as can lay hands on it to push it into a large metal transport box. Alex Few stands on a tire, leans in, and pushes. Stephenson calls, “Push the legs in before you let go of them!” The sheep kicks the metal noisily.

The animals will travel by truck 75 miles north to Lee Vining, where another helicopter will take them into Yosemite. News footage later that day will show Stephenson, Few, and another team member, each standing atop a box. On cue they pull up the doors. The bighorn run dizzily into their new surroundings, like spooked trout in a pool. Each now has an ear tag and two fresh radio collars—one for satellite GPS, the other for close-in tracking.

After five days of this, ten ewes and three rams have been placed inside Yosemite, and seven ewes and four rams in Sequoia National Park to the south.

Stephenson estimates that around 30 more ewes, properly distributed, are needed to rescue the bighorn from endangered status. “The way they’re taking off, that could be in less than five years.”

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