Despite overall numbers in the tens of thousands, mustang advocates say the wild horse is on the verge of extinction in North America.
They say the icon of the American West deserves protection under the Endangered Species Act alongside grizzly bears, the desert tortoise and humpback whales.
The Cloud Foundation and Friends of Animals filed petitions earlier this month with the U.S. Fish and Wildlife Service to list the wild horse as threatened or endangered.
They cite growing threats from development, livestock grazing and government gathers that they say jeopardize the genetic viability of individual herds in 10 states from California to Montana.
The petition says the mustang herds are isolated and their habitat has shrunk 40 percent since President Nixon signed the Free Roaming Wild Horse and Burro Act into law in 1971.
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