The U.S. Fish and Wildlife Service has rejected a proposal to list the North American wild horse as a threatened or endangered species.

Friends of Animals and The Cloud Foundation filed a petition last summer seeking Endangered Species Act protection for tens of thousands of mustangs they say are threatened with extinction on federal lands across 10 Western states from California to Montana.

The conservationists argue the horses constitute a distinct population segment that has evolved as a native species over thousands of years separate from domesticated horses.

But in a new 90-day finding refusing to study the matter further, the Fish and Wildlife Service concluded, effectively, that a horse is a horse.

“Although behaviors between domestic and wild, or feral, animals of the same species may differ ... we find that the petition does not present substantial information that the North American wild horse may be markedly separate from other populations of horse as a consequence of behavioral differences,'' the agency said last week.

The petition said mustang habitat has shrunk 40 percent since President Richard Nixon signed the Free Roaming Wild Horse and Burro Act into law in 1971. It advanced an argument the Bureau of Land Management long has rejected — that the wild horse is a native species that only temporarily went extinct on the continent 11,000 to 13,000 years ago before Spanish conquistadors reintroduced it to North America in the 1500s.

BLM maintains today's American wild horses are not native.

“American wild horses are descended from domestic horses, some of which were brought over by European explorers in the late 15th and 16th centuries, plus others that were released or escaped captivity in modern times,'' BLM's web site states.

Jennifer Barnes, a lawyer for Friends of Animals based in suburban Denver, said the group is disappointed and “a little confused'' by the agency's finding.

“These horses are different, they are treated different under the law, they behave differently and there's some evidence they are genetically different,'' she said.

Barnes said they intend to seek more details before deciding whether to refile an amended petition as part of an effort to slow roundups of mustangs by the Bureau of Land Management.

BLM spokesman Tom Gorey said his agency had no comment on the decision but remains committed to maintaining healthy herds of wild horses and burros on public rangelands.

The Nevada Cattlemen's Association and the Public Lands Council were among those opposing the listing.

“Listing wild horses under the ESA — which is meant for wildlife, not domesticated, non-native animals — would only serve as another demonstration of just how damaging that statute is,'' said Dustin Van Liew, the council's executive director.