The U.S. federal government has downgraded the protected status of the last mountain caribou herd that ranges from Canada south into the United States — a herd on the verge of dying out.

Five years ago there were close to 50 animals in the South Selkirk caribou herd, which roams from southeastern B.C.'s Kootenay region into Washington State and Idaho.

Now, just 18 remain in the herd.

B.C. biologist Leo DeGroot says it's possible some caribou may have been missed during this year's count in March, but he doubts it.

"It's definitely disappointing," he said. "This isn't the first time we were down in numbers. We had 46 in 2009 and it's been a steady decline since."

Biologists have now collared a half dozen of the remaining herd to discover why they are dying, but DeGroot says attacks by wolves may be part of the problem.

Snowmobilers compete for herd's U.S. habitat

The bi-national Selkirk population has been protected in the U.S. since 1983 under the Endangered Species Act.

Caribou once ranged across much of the U.S.'s northern tier but disappeared 100 years ago in all but a small and remote area of the Idaho Panhandle and northeastern Washington.

Mountain caribou

Mountain caribou are the same species as other caribou but have adapted to harsh winters with deep snow by developing dinner-plate sized hooves that work like snowshoes. They eat only arboreal lichens during the winter months. (Garry Beaudry/B.C. Forest Service/AP)

The extirpation, or local extinction, of the Selkirk mountain caribou would mean the end of wild caribou roaming the states below the 49th parallel.

Yet, on Wednesday, the U.S. federal government downgraded the protected status of the herd from endangered to threatened.

The U.S. Fish and Wildlife Service made the change in response to a petition from the Pacific Legal Foundation, Bonner County and the Idaho State Snowmobile Association, which said the herd in the U.S. was too small a subset of animals to warrant listing.

The groups were seeking the removal of all protections from the herd in northern Idaho. A spokesman said the downgrade in status may lift some of the most severe restrictions on activities in caribou habitat.

The Pacific Legal Foundation argued that caribou should not be protected because there are plenty in Canada. But environmentalists countered that the Endangered Species Act specifically allows protection of distinct populations.

Conservation groups have sued for the establishment of a protected critical habitat and to close a large area of the Selkirks to snowmobiles, which pose a threat to the animals.

The Fish and Wildlife Service originally set aside more than 375,000 acres of critical habitat, but pro-business groups complained that would decimate the economy of the area. The habitat was eventually reduced to about 30,000 acres, a decision that remains in litigation.

With files from the CBC's Bob Keating and the Associated Press