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.

They’re stepping up research into how bighorns fall prey to pneumonia, parasitic lungworm and other diseases.

They’re trying to revive dying herds. They euthanized the last ailing bighorns in Poudre Canyon last year and transplanted 15 healthy sheep from crags above Georgetown – hoping these will colonize the canyon.

They’re posting more tourist-management signs, such as the one at Echo Lake Lodge that warns: “Your food kills me because my young learn to beg rather than forage.”