The biggest threat to wild sheep? Domestic sheep

VAIL – A plan to build 61-residential units on bighorn sheep habitat in East Vail recently brought new attention to a dwindling sheep herd native to that area.

Wildlife biologist Gene Byrne studied the local bighorn sheep population in the 1990s using tracking collars. He got to know the herd well and discussed it with the Vail Planning and Environmental Commission in August, including possible reasons for the herd’s decline over the past two decades. The most recent count is 41 sheep, down from 125 in the 1990s.

While the incipient development in East Vail makes Byrne nervous for the future of the herd, he says native sheep are most threatened by their domesticated cousins, wayward “old world” sheep like the one found on the balcony of a home in West Vail this week. The sheep’s owner said it got spooked by a bear and separated from its herd.

“The biggest threat to this bighorn sheep herd is probably not so much development; it’s close association with domestic sheep and pneumonia,” Byrne said. “This is something we really didn’t understand until about 30 years ago, but old world sheep, domestic sheep, carrying pasteurella multocida or other forms of pneumonia, can survive it … but they get in close association with wild bighorn sheep, and they do associate nose to nose, and it’s always fatal to (the bighorn sheep.)”

Byrne said while they didn’t know it at the time, the legislators in Colorado who noted a sharp decline in native sheep populations in the 1880s — prompting them to ban bighorn sheep hunting in 1887 — may have been reacting to a problem created by domestic sheep.

Bighorn sheep were “one of the most common ungulates” found by early settlers in Colorado, Byrne said, “but that was about the time they brought in domestic sheep.”

Local U.S. Forest Service district ranger Aaron Mayville says the Eagle-Holy Cross Ranger District has long been aware of the threat domestic sheep create for native sheep, and the permit for the grazing area from which the sheep found Tuesday had escaped ends well shy of East Vail.

“The herd is in the Davos area right now, and heading (west),” Mayville said Tuesday. “Based on what we know of where the bighorn sheep herd is, and where the domestic herd is, there’s a lot of distance in between.”

Mayville says the Forest Service takes the threat of domestic sheep very seriously when it comes to protecting native sheep.

“It’s explicit in our annual operating instructions that domestic and wild sheep remain separate,” Mayville said.

But Byrne says there are other grazing allotments in the Gore Range, and some of those allotments are a little too close for comfort. An allotment in the Slate Mountain area of the Eagle’s Nest Wilderness runs near an area Byrne observed the East Vail sheep migrating through during collar studies performed in the 1990s.

“I knew that some of those sheep would spend the early part of the winter in Black Creek and Brush Creek and Slate Creek, and then they would make this absolutely incredible migration right across the spine of the Gore,” Byrne said.

“If there was ever an opportunity to buy out those allotments or convert them over to domestic cattle, it would be a very beneficial thing for this herd,” he added.

Mayville said while that’s always a possibility, the Forest Service would have to see a detailed environmental analysis before a use conversion could occur on an allotment.

“Those kinds of things have happened before, but I’ll say it’s pretty rare,” Mayville said.

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