BONNERS FERRY, Idaho — The only caribou left in the contiguous United States are here in northern Idaho where they number about a dozen and live deep in the forests of the jagged Selkirk Mountains, near the Canadian border. Because they are so rarely seen, the caribou — America’s version of reindeer — are known as gray ghosts.

They may very soon become real ghosts: These animals are among the most endangered species in the lower 48 states.

“Right now, predation is the biggest problem, primarily wolves and cougars,” said Norm Merz, a wildlife biologist with the Kootenai Tribe of Idaho, which has contracted with the United States Fish and Wildlife Service to create a plan to revive the population. Not that long ago, hundreds of the animals lived in the United States.

Part of the problem is that the Selkirk herd is international. The caribou can be found in the snowy old-growth forests of Idaho and extreme northeast Washington, but spend about 90 percent of their time in southern Canada. The threat to the animals there is so serious that Canadian government sharpshooters began killing wolves from helicopters. In the Selkirk Mountains, they have killed just 19 so far.