Biologists scramble to stop decline of bighorn sheep population in Colo.
the denver post
MOUNT EVANS – Bighorn sheep once just about posed for Barb Day when she crept across their High-Country habitat with her camera.
Now, in the latest twist of an ecological saga, non-native mountain goats are displacing the sheep along the road from Echo Lake Lodge to Mount Evans’ 14,264-foot summit.
“You miss them,” said Day, who has run the lodge for 31 years.
She and others who sense trouble are correct.
The long-term survival of bighorn sheep – Colorado’s curly-horned state animal – is far from assured, with the sheep facing heavy threats here and across the West.
Colorado Division of Wildlife data show bighorn numbers statewide decreased by 10.2 percent between 2001 and 2009 – from 7,690 to 6,903.
Construction carving into their habitat and disease attacking their lungs – combined with vehicular traffic and livestock – are identified as stress factors.
Hunters kill an average of 157 bighorns a year.
Federal biologists contend that competition from mountain goats – introduced in 1948 by Colorado wildlife managers – could push bighorns over the brink.
The most heralded herd of 335 bighorns above Georgetown – the one along Interstate 70 that people snap pictures of – is producing only 10 to 12 lambs per 100 ewes, said Rick Kahn, terrestrial- wildlife-management supervisor for the state.
That is less than one-third of what a healthy herd should produce.
“It’s fair to say that, of all the big game in this state, the bighorn species is the one we are most concerned about,” Kahn said.
In the 1990s, Colorado emerged as a haven for bighorns, as herds in Wyoming, Montana, South Dakota and Idaho dwindled.
Colorado officials envisioned sustaining 20,000.
Today, state biologists are scrambling to stop the nine-year decline.
“Right now, we don’t have one thing we can point out and say: This is really working,” Kahn said.
The development of Colorado’s High Country increasingly blocks bighorn migration, weakening herds by denying them genetic diversity, said Steve Torbit, director of the National Wildlife Federation.
“We have isolated populations,” Torbit said.
And then there are the goats.
The nine goats that state wildlife managers transplanted to mountains near Salida multiplied to more than 1,500 and spread. About 140 live on Mount Evans. Some have crossed north of I-70.
Researchers recently recorded an encounter between the species. A snow-white goat approached three bighorn sheep licking salt. The goat lowered its dark horns and charged. The sheep scattered, and the goat took over, savoring the salt.
In Rocky Mountain National Park, federal wildlife rangers plan to remove any goats they spot. Mountain goats are a non-native species that spreads disease to bighorns, said park spokeswoman Kyle Patterson.
The park’s bighorn population has plummeted from 600 in the 1980s to 360, said park biologist Mary Kay Watry.
“They are a fragile species, even though outwardly they appear to be very strong,” Watry said. “We can’t assume any species is ever completely secure.”
A federal study modeled what goat competition could mean for already- stressed bighorns. It concluded that “bighorn sheep populations would be reduced by up to 50 percent by the presence of mountain goats.”
Colorado officials in the past designated mountain goats as a native species, which allowed them to multiply unchecked.
Today, the state’s Bighorn Sheep Management Plan states: “Mountain goats are often the more aggressive and dominant species and appear to be capable of displacing bighorns.”
State wildlife managers say they increasingly will control goat populations through hunting, which would limit the expansion of goats into areas inhabited by sheep.
At Echo Lodge, Day said she is still uncertain but hopeful. Biologists have been placing salt licks away from the Mount Evans road in surrounding wilderness, trying to lure bighorns away from people.
The displaced sheep might be thriving out there, Day said.
“We want to know if they’re dying,” she said. “That would be tragic for us.”
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