CHRIS MERRILL Star-Tribune environment reporter | Posted: Thursday, September 11, 2008 12:00 am
LANDER - This summer, just south of here, hundreds of visitors to the Shoshone National Forest and Sinks Canyon State Park have enjoyed what has become a relatively rare opportunity:
They've had up-close sightings of full-grown, healthy bighorn sheep.
In many cases the rams have sauntered within a few feet of the gawkers' vehicles, paying the people little to no mind.
And the visitors have had the chance to observe the brawny rams in all their famous splendor - with their 20-pound curling horns and their bright, caramel-colored eyes, which are as efficient as 10-power binoculars.
The 220-pound beasts have been ambling up and down Sinks Canyon Road on a daily basis, as locals, campers and sightseers from out of state have haphazardly lined the shoulders of the thoroughfare with their vehicles to snap photos and otherwise gape and point.
But if a recent trend continues, bighorn sheep viewing like this will become even rarer than it already is today.
The statewide bighorn sheep population has been on the decline in recent decades, and in the past 20 years it has dipped 15 percent, according to Wyoming Game and Fish Department estimates.
The Whiskey Mountain herd, the Cowboy State's most famous, has dwindled to about 700 animals from over 2,000 less than 20 years ago, said Greg Anderson, a wildlife biologist with the Wyoming Game and Fish Department. Anderson has been studying the group in the northeastern portion of the Wind River Range outside of Dubois.
It's not all bad news for bighorns in Wyoming, he said, as other herds throughout the state have seen some upticks in their numbers in recent years.
Still, the general, long-term trend has been a shrinking population.
Evolutionary geneticists believe bighorns originated in Siberian Asia and crossed to North America by way of the Bering Strait more than 700,000 years ago.
Two centuries ago, bighorn sheep thrived in the American West. While it's impossible to know with great accuracy how many there were, biologists estimate more than a million and perhaps more than 2 million of the animals once grazed in current-day Canada, northern Mexico and the United States.
Today, most estimates put the total number below 60,000, with about 25,000 to 30,000 bighorns roaming the North American Rockies.
A variety of factors caused the species to go into decline in the 19th and 20th centuries throughout the West, including white settlement, intense hunting and the introduction of diseases carried by domestic sheep.
"It's a well-accepted idea that domestic sheep carry diseases that they've transmitted to bighorn sheep," Anderson said.
In 1987, there were an estimated 6,680 bighorn sheep in the Cowboy State, according to Reg Rothwell, wildlife biologist with Game and Fish Department. Ten years later the population had shrunk to about 6,240. And ten years after that, in 1997, the statewide bighorn numbers had dropped to 5,680.
A catastrophic outbreak of pneumonia in 1991 decimated the Whiskey Mountain herd, and it went into decline thereafter for about 12 years, Anderson said.
Although the Whiskey Mountain population has stabilized in recent years, it hasn't begun bouncing back. Rather, it's merely been "treading water," he said.
"You have residual disease issues tracing back to the pneumonia outbreak. You have poor forage conditions due to drought. The age structure has skewed older because (fewer lambs are surviving). You have predation. And you have a high load of lungworm," Anderson said while observing the herd on Torrey Rim this spring. "I suspect that all of those are factors in what's going on up here."
Lungworm is a parasite common to sheep that isn't fatal on its own, but damages the lungs and causes scarring. The burden of the parasite and the scarring makes the animals more susceptible to diseases such as the bacterial pneumonia that wiped out so many bighorns 17 years ago, Anderson said.
The Game and Fish Department believes while lungworm isn't the cause of the Whiskey Mountain herd's decline, if the lungworm were removed from the equation at least for a few years, more lambs would probably survive, and the population could recover.
Anderson plans to give the Whiskey Mountain bighorns medicated feed this winter to rid the animals of the parasite. When the new crop of lambs arrives, with a little luck, a higher percentage of them will survive to be adults, he hopes.
Environment reporter Chris Merrill can be reached at chris.merrill@trib.com or at (307) 267-6722.
The once-in-a-lifetime experience of bighorn sheep hunting is among the subjects featured in the inaugural edition of Wyoming Hunter & Angler, inside today's paper.]]->
The estimated number of bighorn sheep in Wyoming over the past two decades:
2007 5,681
1997 6,244
1987 6,676
Source: Wyoming Game and Fish Department]]->