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Study looks at why bighorn sheep in Cody area do better
Wyoming Game and Fish Department large carnivore biologist Luke Ellsbury, left, and WGFD wildlife biologist Cole Hansen readied a tranquilized bighorn ewe for transport to a waiting horse trailer for examination. Photo by Gib Mathers/Powell Tribune

Study looks at why bighorn sheep in Cody area do better than elsewhere

Mar 20, 2014 - By Gib Mathers, Powell Tribune

POWELL -- The dart swatted the bighorn sheep ewe square on the rump, making her a winner of sorts.

Little did the ewe know she had been picked to be included in a multi-state study between Wyoming, Colorado and Montana. The Wyoming Game & Fish Department and others are endeavoring to ascertain why bighorn sheep in the Cody region are doing well despite pathogens that can cause disease.

They plan to use that knowledge to understand why other bighorns around the West packing the same pathogens are not faring quite as well.

On Feb. 19-20, 16 bighorn ewes and one ram were captured on the North and South Forks of the Shoshone River.

This is the second year of a three-year multi-state study to determine how bighorns cope with disease, said Hank Edwards, Game & Fish laboratory supervisor from Laramie.

After standing with a tranquilizer dart protruding from her butt for a few minutes, the ewe tried to walk, but her front legs appeared made of jelly and her head drooped.

Another ewe watched like a teetotaler scowling at the town drunk. After a few minutes the drugged bighorn folded into the ground and two Game & Fish staffers dashed to her for a quick and safe transport to a pickup truck.

All the ewes will be hauled to the Thorne-Williams Wildlife Research Unit (formerly Sybille) near Wheatland where she and others of her species will be closely monitored.

The goal is to map where pathogens occur and in which herds. Researchers will then link the pathogens to the herds' overall health to determine how the bighorns are coping with the pathogens, Edwards said.

The 16 bighorns captured near Cody will join 12 bighorns from central Colorado as part of the project.

Lambs in that Colorado herd did not survive to adulthood. Over the next two or three years, the researchers plan to ascertain why the Cody sheep tolerate the pathogens, then determine how that tolerance can build immunity by uniting the Cody and Colorado sheep, Edwards said.

Individually or in concert, Mycoplasma ovipneumoniae, Bibersteinia trearealosi and Mannheimia areaemolytica have been linked to pneumonia in bighorns across the West, but the Cody area bighorns carry all three pathogens, "and they're doing quite well," Edwards said.

"There are over 4,000 (bighorn) sheep in the Absaroka Mountains," said Doug McWhirter, Cody Game & Fish wildlife biologist.

There are an estimated 5,400 bighorns across the state, said Al Langston, Game & Fish spokesman in Cheyenne.

From their first summer to their first fall, lamb survival is about 25 to 35 percent for the Cody-area bighorns, which he ranks as pretty good around here, McWhirter said.

In hunt area 1, near the Clarks Fork of the Yellowstone River, the 20-year average is 33 lambs per 100 ewes. In area 2 near Trout Peak, the average is 32 per 100.

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