Mountain goats threaten Bighorn sheep
For 24 years Steve Cain, a senior wildlife biologist in Grand Teton National Park, has traveled the same routes in the park looking for signs of the area’s small and fragile Bighorn sheep population.
This fall he and his team stopped at the same spot they do every year at the mouth of Webb Canyon. From their lunch spot, the group had a good view of the cliffs above where they almost always spot a Bighorn sheep, drawn to the habitat and the mineral lick.
This year they didn’t see the sheep they were searching for, but instead saw a mountain goat.
“It was a very powerful reminder of the potential threat,” Cain said. “It really had a huge impact on us all. We were so depressed when we saw the goat there and no sheep.”
This year Grand Teton National Park plans to step up efforts to monitor mountain goats, a non-native species that biologists worry is establishing a population in the park and threatening the park’s Bighorn sheep.
Aside from the park’s mission to preserve native species, anytime a piece of the ecological puzzle is removed and replaced with a foreign species that didn’t evolve with the other species of the landscape, there will be implications, Cain said. What those are and how far reaching is often unknown until its too late and the native species has disappeared. Cain wants to make sure that stage isn’t reached in Grand Teton with Bighorn sheep.
Bighorn sheep are a charismatic megafauna known as icons of the mountains and wilderness, Cain said. Not only are sheep important ecologically, they’ve also played a role in the park politically. Before Grand Teton became a park, some legislators in Idaho opposed its creation because they worried nearby ranchers would lose grazing rights in the area, said Jackie Skaggs, park spokeswoman.
Domestic sheep, which can carry diseases, threatened the Teton herd for years. But all nearby allotments have been retired, Cain said.
Evolving in a fragile alpine and subalpine environment Bighorn sheep are also important to ecosystem functioning, Cain said. Living up to about 12 years and breeding in the fall, females have one or two lambs each year. Cougars are the primary predator of the animals, and wolverines and golden eagles prey on the lambs. Bighorn sheep are also susceptible to avalanches in the mountains.
The Bighorn sheep face new challenges. The park’s sheep have been pushed to winter at higher elevations due to development in the valley and also due to fire suppression, which allows forests to grow denser, Cain said. Sheep don’t like areas of heavy cover.
“Their vision is one of their greatest defenses,” he said.
The herd is geographically isolated, which can be a benefit at times. While the nearby Gros Ventre herd has seen pneumonia outbreaks, the park’s sheep haven’t seemed impacted. However, the about 100 sheep that make up two small subpopulations in the Tetons do not inter-breed. The genetic isolation could cause problems for the herd’s long term survival. The population has stayed steady for the last 40 years.
Sheep are the only native ungulate adapted to living in high elevation, rocky craggy areas in the park, Cain said. Those areas have little vegetation in the winter.
“They clearly live on the edge of making it or not,” Cain said.
And a new goat population could be enough to push the sheep population over that edge.
In 1969, Idaho Fish and Game imported mountain goats to an area near Palisades, Cain said. It used to be common to move big game animals outside their normal ranges to establish populations for sport hunting. The goat population thrived. About 10 years later the animals started appearing in the Tetons, but for brief stints.
“We weren’t all that concerned about it,” Cain said.
But in 2008, biologists began to see adult females with young-of-the-year, meaning some of the goats were staying in the park and reproducing.
“Those are the telltale signs of a population establishing itself,” Cain said.
Since then, park staff have seen more goats with young-of-the-year.
Mountain goats are large herbivores that have a significant impact on the ecology of the landscape. In places where they evolved, other species in the ecosystem were able to evolve with them, Cain said. But anytime a species just drops into a new ecosystem, the other species aren’t prepared for it. Olympic National Park has struggled with goats that were transplanted to the Olympic peninsula, Cain said. They’ve had significant impacts on the alpine ecology.
Mountain goats are more aggressive than Bighorn sheep and the two animals do have some overlapping habitat, Cain said. If there is limited winter range, the goats will dominate it.
Goats also can carry diseases that can affect the sheep.
There are believed to be only about 20 or fewer goats in the Tetons, but that population could grow rapidly.
This year the park plans to ramp up its monitoring of mountain goats, including fitting some with radio collars. Staff already ask people to report goat sightings in the park.
The park also will begin work on a management plan for mountain goats, which will go through a public process and give direction for the current situation and as well as how to mitigate similar future threats, Cain said.
“It took more than 40 years for this transplant population down in Idaho to become an issue in the Tetons,” he said. “It could take another 40 years before there is another problem.”
Cain said he’d love to begin work on a management plan this year and potentially finish it in two years.
It’s not too late to make a difference for the sheep, he said.
This fall when his group hiked out of the canyon five days after seeing the goat, they spotted a Bighorn sheep in the same place. The goat was gone.
— “Peaks to Plains” is a blog focusing on Wyoming’s outdoors and communities. Kelsey Dayton is a freelance writer based in Lander. She has been a journalist in Wyoming for seven years, reporting for the Jackson Hole News & Guide, Casper Star-Tribune and the Gillette News-Record. Contact Kelsey at firstname.lastname@example.org.
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