Deaths of the Little Bighorns
The baby bighorn sheep stumbled and collapsed on the stony tundra, too sick and wobbly to keep up with its mother.
Jon Mionczynski, a wildlife researcher who followed the pair, had seen this before. For some reason, lambs born into the largest herd of bighorn sheep in the Rockies were not surviving.
It would be hard to find a wilder, safer sanctuary, or so it seemed. But as scientists teamed up with Mionczynski to unravel the mystery, they learned that there is no such thing as pristine wilderness and no refuge from the Industrial Age.
Mionczynski nicknamed the struggling lamb “Rambo” because of its tenacity and pluck. Each time it fell, it struggled to its feet, even after blinding an eye in a tumble.
One evening, he was close to capturing Rambo for testing, but the lamb and its mother started down the mountain and, out of reach, hunkered down in a fortress of boulders near a crag called Lion Pass.
“I returned at daybreak and saw the ewe still guarding the site,” Mionczynski recalled. “She made a low-pitched, throaty bleat, . . . brrrr . . . brrrr. It was like a sheep crying and it just went right through me.”
When he got to the boulders, he saw fresh mountain lion droppings. “The ewe had a torn ear, blood running down her face and claw marks on the side of her head,” he said. “The lamb was gone. That was the end of Rambo.”
In a way, the natural order had prevailed: the strong picked off the weak. But something was unnatural too: What was making lambs so sick within weeks of their birth? Why were ewes leading weak lambs on arduous treks through cougar country to reach mineral licks at the base of the mountain?
The herd, which used to number about 1,250, plummeted by 30% in two years during the early 1990s and never recovered. Since then only about two out of every 10 lambs have survived.
In 1998, the Wyoming Department of Game and Fish told Mionczynski to set up a one-man camp at nearly 12,000 feet, track the herd’s every move, study every foot of their mountaintop refuge, examine plants they eat and send back blood and tissue samples of dead and dying animals.
The job called for a meticulous observer and a skilled outdoorsman, someone who did not fear grizzly bears, or living in a tent in snowstorms and driving winds. For Mionczynski, it was the dream assignment.
“I have the best job in the world,” Mionczynski said. “I’m just a peon in this research, but I like to think I am helping these animals.”
Now, four years into the project, scientists believe they are close to solving the mystery. What they have discovered suggests that profound environmental changes are beginning to ripple through the food chain and into the bodies of lambs. They are learning that even these reclusive bighorn sheep, masters of evasion, can’t escape pollution that falls from the sky.
As a result, Mionczynski and others fear, these icons of wild America may be unable to survive in the wilds without continual human intervention.
Town Takes Pride in Bighorn Sheep
A summer thunderstorm peels off the Winds, a fitting name for the mountain range west of Dubois (pronounced doo-boys), briefly spilling rain and hail over town. Tourists pull off of U.S. 287 into the National Bighorn Sheep Interpretive Center, the newest and most ornate facility in this two-lane town. It’s located past the Ramshorn Inn Tavern, not far from the high school where the Rams play, a couple blocks from the Ramshorn Food Farm on Ramshorn Street.
“This town loves these sheep and we’re proud of them,” said museum Director June Sampson, leaning over the cash register. “In the winter, people can see them with spotting scopes from their living rooms. Hundreds of people come from all over to see the sheep.”
Rocky Mountain bighorns have thrived in these mountains southeast of Grand Teton National Park for centuries. They are stocky and barrel-chested with petite feet that stick to rocks like suction cups. In the fall, rams charge one another and smash heads at speeds of 20 mph in battles that sometimes last all day and all night. Shoshone and Gros Ventre Indian tribes made powerful bows from the horns, which are still prized by hunters as trophies.
The herd inhabits the northern Winds in scattered bands. When they all converge on the sagebrush hills at the edge of town during winter, they constitute the largest group of wild sheep in North America. These animals were once so abundant that they were transplanted to establish new populations from South Dakota to New Mexico to Idaho.
Yet there are fewer and fewer sheep for tourists to enjoy. Barely 800 animals remain in the herd, which is still in decline. That prompted Wyoming game managers to dispatch Mionczynski to the mountaintop.
No sooner had Mionczynski set up camp on Middle Mountain in June 1998 than he observed many lambs as feeble as Rambo. Born healthy, they grew sick shortly after ewes made their annual spring migration to Middle Mountain to forage. If pneumonia didn’t kill them, predators did.
“Some were crawling on their knees. They were so sick they couldn’t even get up to nurse. Their muscles just seemed so stiff and they had trouble breathing. They stuck their noses in the air, mouths open, gasping for air,” Mionczynski said.
Ranchers in the lowlands reported that the ewes ate dirt at washed-out mineral licks. It helped explain why ewes were leading their sick lambs down the steep mountain to sagebrush flats that they normally visited only in winter. Something essential was missing from their diet. The route traversed some of the roughest country in the Winds, including a series of cougar ambush spots in Lion Pass.
Eventually, Mionczynski observed that lambs who nursed from the ewes that made the journey to lowland mineral licks did much better.
The challenge was to find the missing ingredient in the mountain forage.
Working in a makeshift lab fitted into a cave in the boulders, Mionczynski began testing plants the sheep eat. He discovered that selenium, a nutrient, had dipped to alarmingly low levels.
Selenium is a peculiar, sulfur-like element essential for many mammals. It is a naturally occurring nutrient with a twist. Just a little is needed to ensure bones, muscles and immune systems develop properly, but just a little more can be toxic.
Tests on Middle Mountain showed 5 parts per billion of selenium in forage favored by bighorns--75% lower than the minimum requirement for a healthy immune system, according to veterinarians.
Wild sheep with weak immune systems are candidates for a variety of ailments. But the symptoms they exhibited strongly suggested white muscle disease, said Pat Hnilicka, wildlife biologist for Wyoming who supervises the bighorn project.
White muscle disease is a form of muscular dystrophy; muscles deteriorate and fail to support the skeleton.
“We see these symptoms in a lot of the [bighorn] lambs, the stiff-legged gait, poor coats, infections. We saw lots of periodontal disease in those sheep, too, which indicated susceptibility to infection, an indicator of poor immune system,” Hnilicka said. “These are all symptoms that are consistent with a selenium responsiveness disorder.”
But how could selenium be in short supply? Soils across much of the West are awash in it. In nearby Dubois and other parts of Wyoming, range cattle are sometimes poisoned from ingesting too much of it.
The selenium content in plants fluctuates with weather, rising in dry years and falling in wet. The fluctuations correspond neatly with a 30-year lamb survival trend, with fewer surviving in wet years, scientists say.
At the same time, the chemical content of rainfall was changing. So was the composition of the soil that absorbed it.
For at least a decade, according to scientists, storms have been carrying larger and larger amounts of chemical contaminants and dumping them across the Rockies. Among the chemicals are nitrates and ammonium, which can saturate the environment with nutrients or create acidic conditions similar to those that plague forests in the Northeast and Canada. The phenomenon is known as acid rain.
Acid rain is declining in the East, but across the West fast-growing cities are pumping more and more nitrogen-based compounds into the atmosphere. Transported long distances and released by winter snow and summer thunderstorms, the chemical loads are dumped in places like the Winds. And unlike the East, where forests can utilize nitrogen, alpine regions in the Rockies lack the lush vegetation that absorbs nutrients or buffers acids.
According to the U.S. Environmental Protection Agency, 50% more nitrate is falling near Gunnison, Colo., and at Chiricahua National Monument in Arizona compared with a decade ago. In Wyoming, virtually every sample site shows dramatic increases in nitrate deposition since 1986; twice as much has been measured in Yellowstone National Park over that time.
At the bighorn camp on Middle Mountain, scientists tracking storms and wind currents have traced the sources of pollutants that blow in from hundreds of miles away. They come from industrialized regions of northern Mexico, from coal-fired plants in Arizona and Utah and from tailpipes and factories in Los Angeles. Sometimes, the jet stream from the Pacific Northwest carries ammonium, possibly from fertilizer plants in Idaho, according to scientists.
On the one hand, the pollutants fertilize plants and microorganisms. On the other hand, they can saturate soil and water with nutrients, causing toxic algae blooms, harmful acids and changes in soil chemistry. Researchers at UC Riverside found that nitrogen compounds in smog promote alien grasses, but kill a native shrub community sustaining rare species, downwind of Los Angeles. In Colorado, scientists have recorded wholesale changes in aquatic algae in the Green Lakes Valley near Boulder.
“We’re pushing the first dominoes in the food chain and there’s good evidence it’s increasing and probably in response to nitrogen deposition,” said Mark Williams, a hydrogeochemist and fellow at the Institute of Arctic and Alpine Research at the University of Colorado. “We’ve reached a threshold and we’re at that slippery slope where we are headed toward dead fish and dead trees.”
Near Colorado’s Rocky Mountain National Park, scientists have begun an experiment to see whether pollutants are short-circuiting the selenium cycle and contributing to declines in a bighorn herd at St. Vrain Canyon, said Rob Roy Ramey, chairman of zoology at the Denver Museum of Nature and Science.
“Urbanization and sheep deaths seem to go hand in hand. We know there’s a lot of acidification of the front range of the Rockies, and this offers a perfectly reasonable and clear mechanism. It’s a hypothesis, but it’s very plausible,” Ramey said.
In the Wind River Mountains, researchers strongly suspect that wind-blown pollution is at the root of the bighorn sheep deaths. They advance two theories.
One holds that added nitrogen deposited in wet years stimulates and changes microbes in the soil, which in turn convert selenium to a gas that escapes before plants can absorb it, said Jack States, microbial ecologist at Northern Arizona University.
On the other hand, Bruce Mincher, chemist at the Department of Energy’s Idaho National Environmental Laboratory, is studying whether extra precipitation, in conjunction with nitrates, affects oxygen available to convert selenium into forms available for plants.
On Middle Mountain, an array of plots of native grasses are fitted with shields and electrical probes in an attempt to see how vegetation absorbs selenium under carefully controlled conditions. The work, which has cost $143,000 so far, is continuing.
Nevertheless, the researchers say that the air pollution connection so far best explains all the data they have collected on the herd inhabiting the Winds.
“We know that deposition of nitrates falling on those high alpine areas is changing soil chemistry, so selenium is not available for plant uptake,” Hnilicka said. “There’s a connection between the health of the bighorn sheep and the air quality, but we don’t fully understand it yet.”
Debate on Whether Humans Should Step In
Lanky and tireless, Mionczynski, 54, is a happy recluse, which is good because in four years he has seen humans on Middle Mountain just once, not counting scientists supervising the research or sheep hunters. He eats native plants, bathes in a frigid creek and scrambles across boulders as effortlessly as the bighorns.
By day he tracks sheep, checks rainfall gauges and maintains study plots of scruffy tundra and alpine grassland, which the sheep eat. At night he watches the Milky Way and listens to distant waterfalls rumbling through darkness before retiring to a tent full of books. The landscape is stark and treeless, punctuated by towering stacks of boulders that glaciers left behind after the Pleistocene. It is a realm of immense sky and granite precipices, turquoise lakes and glaciers, bone-chilling ice storms and lightning that strikes like artillery.
It is hard to see such a place as a breeding ground for an epidemic. The Winds are a picture of unspoiled wilderness.
Across the canyon from Lion Pass is a velvety green meadow where moose and elk roam. Mionczynski relaxed atop a boulder as a bald eagle soared over Torrey Canyon far below and a weasel just beyond his boots watched him warily.
“Just because you cannot see the contaminants doesn’t mean they are not there,” he said.
Two years ago, game managers used helicopters to drop selenium-rich mineral blocks at the edge of a cliff on Middle Mountain. Ever since, lambs have been healthier, although not enough of them have survived to restore the herd.
But the efforts to save the sheep have triggered a whole new debate.
Biologists are divided over the use of mineral licks to sustain wild animals. While they provide essential nutrients, they also attract predators, including hunters, who know animals are attracted to them. There is also a higher risk of disease transmission when animals congregate around them.
And, however subtly, human intervention signals that a species has lost some of its wild character.
“When does this stop? Does this go on in perpetuity?,” asked Meredith Taylor, an outfitter in Dubois and a member of the Wyoming Outdoor Council, a conservation group. “Do we want to create species that are dependent on humans feeding them? They become wards of the state. It’s very sad.”
Mionczynski has heard the argument before. He’s been shouted down in town hall meetings over the issue, though his response sounds philosophical and pragmatic: “Humans have already interfered with the natural order up here. You can leave the sheep alone and lose them, or have limited human involvement and keep the sheep. We’re just trying to help them.”