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Advocates are petitioning the U.S. Fish and Wildlife Service to list wild horses as threatened or endangered, which would trigger protections for herds in 10 Western states.

Setting aside the question of whether there are too many or too few horses — a debate raging throughout the West — the wildlife agency will have to consider a perennial question: Are wild horses native to this country?

To gain endangered or threatened status, a species must be in danger of going extinct and generally, it must be native.

The prevailing wisdom — and the position of the Bureau of Land Management, which manages wild horses — is that wild horses are not native because humans brought them to the continent.

Friends of Animals and The Cloud Foundation argue in a petition filed June 10 that horses are both going extinct and, indeed, a native species.

The two nonprofits contend wild horses on the public range face extinction because of loss of habitat to cattle grazing, mining, energy exploration and urban expansion, as well as the BLM's controls, which limit the horses to small herds on isolated ranges, require frequent roundups and are headed toward sterilization of horses.

And they point to prominent researchers who, contrary to long-standing assumptions, consider wild horses a native species.

Ross MacPhee, an evolutionary biologist and curator of mammology at the American Museum of Natural History, says it's "complete absurdity" to consider wild horses as non-native.

Their ancestors evolved on this continent millions of years ago, and some migrated over the Bering Strait land bridge that then connected North America to Asia.

With many other large mammals, they went extinct on this continent 11,000 to 13,000 years ago, and their descendants did not return until the 1500s, with Spanish conquistadors. Today's wild horses descend from those ponies and from generations of horses that escaped or were released by their owners in the West.

That wild horses' ancestors were once domesticated "doesn't change the fact that all horses today are the same species" — and that the species evolved on this continent, says MacPhee.

"There is (no mammal) more American, that is still with us today, than horses," MacPhee says.

Both the fossil record and new genetic research point to significant similarities between ancient equids and today's horses, he notes.

The advocates' petition quotes another expert, Jay Kirkpatrick, a Montana wildlife biologist who has worked on birth control for wild horses for decades.

Federal agencies that regard wild horses as non-native, feral, or exotic don't only fail to understand modern science, Kirkpatrick co-wrote in a 2010 paper. That viewpoint is "also a reflection of their desire to preserve old ways of thinking to keep alive the conflict between a species (wild horses), with no economic value anymore (by law), and the economic value of commercial livestock."

Robert Garrott, a Montana State University wildlife biologist who served on the National Academy of Sciences (NAS) research panel that spent two years studying the wild horse issue, disagrees.

Today's wild horses are "entirely different" from those that evolved in North America, says Garrott, director of fish and wildlife ecology at Montana State.

Not only are the horses the result of hundreds of years of human breeding and trade, "the ecosystem, the climate, everything has changed over geologic time," he said.

Garrott sees the petition as a move to try to stop all horse population management by the BLM, and to remove livestock from the range to accommodate more horses.

Steven Petersen, a rangeland ecologist at Brigham Young University who also served on the NAS panel, says it's almost irrelevant whether wild horses are a native species.

We can't duplicate the world the ancient horses inhabited, with saber-toothed cats, other predators and plants that no longer exist, he notes.

The larger problem with the petition to list wild horses as endangered is the fact their numbers are "exploding," Petersen says.

The NAS report, issued a year ago, says that if BLM does not intervene with birth control and other science-based management tools, 10 Western states can expect wild-horse populations to double every four years.

Garrott and Petersen fear the United States could find itself with so many horses, and such a degraded range, that it has to do what Australia is now doing: shooting camels and horses from airplanes.

Many wild-horse advocates say the BLM overestimates the number of horses.

In the petition filed this month, the advocates also say the BLM's practice of allowing horses only in herd management areas creates gaps in the natural biodiversity of North America.

"Such gaps negatively influence the overall distribution of flora and fauna, and place various North American ecosystems in jeopardy of collapse," the petition reads.

This apparently is the first time wild horses have been proposed for listing as endangered or threatened.

"We aren't aware of having received a petition in the past to list the wild horse in the U.S.," a spokeswoman wrote in an email last week.

The agency has 90 days to decide whether the case for listing is "substantial" enough to warrant more study.

Twitter: @KristenMoulton —

Wild horses: By the numbers

The Bureau of Land Management says that as of March, there were 49,209 wild horses and burros on western ranges, 22,500 more than its management objectives allow, given the need for ecological balance with other species and uses.

By contrast, there were 17,300 horses and 8,000 burros when the Wild Free-Roaming Horses and Burros Act took effect in 1971.

The BLM says it has found homes for 230,000 wild horses and burros in past decades, but still has 49,000 in captivity, most of them in long-term pastures in the Midwest.

Wild horse advocates contend the BLM overstates the number of horses on the range now, and underestimates how many there were in the past.

While advocates believe there were 2 million to 7 million wild horses in the late 1800s and early 1900s, BLM says, on its Myths and Facts website, that "this mythical figure has no historical basis; it is complete speculation." #

Horse exhibit

The Natural History Museum of Utah will open an exhibit, The Horse, on July 21. It will run through Jan. 4.

The exhibit will explore the connection between humans and horses, and will look into the Ute tribe's use of horses.

The show was organized by The American Museum of Natural History in New York.