RENO, Nev. (AP) — Despite overall numbers in the tens of thousands, mustang advocates say the wild horse is on the verge of going extinct in North America for the second time in 13,000 years and deserves protection under the Endangered Species Act alongside grizzly bears, the desert tortoise and humpback whales. Efforts to halt mustang roundups in Congress and the courts have been unsuccessful over the past decade, but two groups in a petition to the U.S. Fish and Wildlife service are focusing on genetics and research they say prove the horses are a native species.

They say growing threats from development, livestock grazing and government gathers are jeopardizing the genetic viability of individual herds in 10 states from California to Montana. The petition states mustang habitat has shrunk 40 percent since President Richard Nixon signed the Free Roaming Wild Horse and Burro Act into law in 1971.

It advances an argument that 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.