SEVERE WINTER FOR BIGHORN SHEEP
John Wehausen picks up the mountain lion’s severed head. He’s outside the CDFW (California Department of Fish and Wildlife) office in Bishop. A handful of others and I stand around him in the sun, which heats us and the skulls on the concrete sidewalk. Sierra bighorn sheep.
Wehausen’s been studying the sheep since 1974, and he’s here with Ginnie Chadwick to help lead the Sierra Nevada Bighorn Sheep Foundation’s field trip.
Chadwick — who handles much of the foundation’s educational programs with schools, scouts, etc. — and Wehausen have been swapping bighorn facts with us for about thirty minutes. The mountain lion’s a big predator of the sheep, says Wehausen. The lion’s head withers in the heat.
At another point, he picks up a sheep skull and pulls the keratin horn off its bone structure. Bighorn sheep don’t shed their horns. Each layer of keratin’s a year. Like tree rings, you can count them.
The info session ends. We pile into our cars and drive past Big Pine and up some dirt roads. We park. Stare at the hillside. “Oh!” someone says. “I see them!” Word spreads among our group. People point. “Where?” “There!” “They look like rocks.”
It takes me a few minutes, but I find them. About thirty pinpricks of stone-colored fur. Munching the hillside plants. Chadwick peers at the sheep through her binoculars. “I still get chills everytime I see them,” she says.
The Sierra Nevada Bighorn Sheep Foundation was founded in ‘95. The goal: keep the bighorn sheep alive. In ‘99, the foundation got California and the federal government to list the sheep as an endangered species.
These days, foundation volunteers assist in the CDFW’s efforts to recover the species by buying things like radio collars and spotting scopes. They also help with the cost of the helicopters used to conduct sheep captures, translocations, and research.
Yeah. Sheep captures.
Chopper comes in, someone fires a net gun, sheep gets netted, then dragged, beneath the chopper, through the air. To a research station.
“We don’t tranquilize them,” said Chadwick. Instead, researchers blindfold the sheep. “Once the blindfold goes over their eyes, they think they’re dead.”
The sheep don’t move. Researchers get their data. Then, it’s back to the helicopter, and the sheep are deposited (blindfolds off) in the same spot from which they were taken.
This winter’s been tough on the sheep.
“In winters like this,” says Tom Stephenson — CDFW environmental scientist and the program leader for the Sierra Nevada Bighorn Sheep Recovery Program — “when [the sheep] just keep getting hammered by storm after storm, they’re really relying on their fat reserves to make it through the winter.”
Some of the sheep go into the winter with something like 30% body fat, Stephenson tells me. Some calculations show that an animal with that much fat can survive up to 80 days on its fat reserves.
But, when the snow keeps falling, food sources get scarcer and sheep have a tough choice to make: stay put and starve, or go out and spend a bunch of energy looking for food that might not be there.
So, they die of starvation. Or get buried by an avalanche.
Then, there are the mountain lions. Before Americans moved west and colonized California (bringing domestic sheep and killing any and all predators), researchers believe the Sierra’s ecological system worked something like this…
There were more bighorn sheep in the mountains than deer. Because the wolves killed a lot of deer (deer are wolves’ primary prey), and the winters killed a lot of deer. “If there were fewer deer on the landscape,” says Stephenson, “there would be fewer lions on the landscape. Plus, you would also have some direct competition between wolves and lions … so, in general, we think that in all likelihood, there was just less predation on bighorn sheep by lions than what we’re seeing now.”
The lions wouldn’t be too much of a problem if there were more bighorn sheep out there. Since the 1970s, recovery efforts have turned three populations of Sierra bighorn sheep into 14. Still, it’s not enough to be comfortable with the chronic lion activity that’s been occurring.
All of this — the snow, the mountain lions, the winter — makes for a Sierra bighorn survival rate of 50%.
Meaning, this winter, 50% of the Sierra bighorn sheep have died.
There’s a silver lining, though. A severe winter kills a lot of sheep. “But, what [a severe winter] also does is provide a tremendous amount of moisture that creates high quality habitat,” says Stephenson. “And so, if these severe winters are just sporadic, then the populations actually — as long as there’s enough animals that remain — they’re able to rebound really quite quickly.”
Around 12 p.m., Chadwick lets us field-trippers know that we can leave. Many linger by the scopes. The sheep are still up on the hillside, eating their plants, sometimes staring back.
“They’re all looking in the same direction,” said a woman to my right.
“So are we,” I said.
The sheep are beautiful. Knockout strong. Their horns spiral out, then in, depending on their age and gender.
I take a last look, hop into my car, and drive home.