A Mexican gray wolf called Asha wandered hundreds of miles across Arizona and New Mexico searching for a mate — no easy task for one of the most endangered mammals in the United States.

After five months of scouring hills and arroyos, she crossed Interstate 40 west of Albuquerque in the fall of 2022 and headed into the forests outside of Santa Fe. But when she traipsed across the interstate blacktop, she crossed an invisible boundary set by federal wildlife officials. As part of longstanding federal policy, any Mexican gray wolf found north of the interstate can be relocated — which is why Asha was darted and flown south, as documented in news stories and U.S. Fish and Wildlife Service reports.

The Mexican gray wolf subspecies has made a significant recovery over the last 25 years, but government biologists now worry that the reintroduction of the larger northern gray wolf in Colorado could derail that progress, should the two populations mix via wandering wolves like Asha.

Those worries prompted Colorado wildlife officials in September to sign first-of-their-kind agreements with New Mexico, Arizona and Utah. They will allow those states to relocate any roving northern gray wolves back to Colorado. The agreements will help keep the 10 wolves released in Colorado in December inside the state, crucial to establishing the self-sufficient population mandated by voters who approved reintroducing the species.

“This is not a typical kind of agreement for us to have between states,” said Eric Odell, the wolf conservation program manager at Colorado Parks and Wildlife. “It’s not common practice. Wildlife work usually involves geographic boundaries, not political ones.”

Much is at stake with the Mexican gray wolf. Its recovery took hold through an extensive, decades-long effort involving a captive breeding program, international transplantations and ongoing litigation.

The states’ recent agreements, coupled with the U.S. Fish and Wildlife Service’s I-40 policy, will create a buffer zone between the two wolf populations.

Without the precaution, Odell said intermixing could result in Colorado’s larger northern gray wolves taking dominant breeding positions in packs, changing the subspecies’ gene pool until they are indistinguishable. In effect, government biologists believe northern gray wolves likely would take over the Mexican gray wolf population.

“Having that hybridization would become detrimental to the Mexican wolf,” Odell said. “We’re working hard to keep (northern gray wolves) separate from those Mexican wolves.”

But conservationists question whether allowing the two to mingle would imperil the rare southern subspecies, and some say the Mexican gray wolf needs the northern gray wolf to survive. The wild Mexican gray wolf population suffers from a limited gene pool, so breeding with the northern gray wolf could help diversify the population.

“Historically, there was a spectrum of wolf species and subspecies from Mexico up to the Arctic Circle,” said Chris Smith, the Southwest wildlife advocate for WildEarth Guardians. “To have this wolfless zone between Colorado and Mexican gray wolves is a bizarre and arbitrary symptom of the politicization of our legal treatment of these wolves.”

A subspecies on the brink

The Mexican gray wolf — also called the lobo — is a smaller subspecies of the gray wolf that historically ranged across Mexico and into Arizona, New Mexico and Texas. The Mexican gray wolf is managed separately under the federal Endangered Species Act than the northern gray wolf, which numbers in the thousands across the northern Rocky Mountains and the Great Lakes region.

People nearly eradicated the Mexican gray wolf from both the United States and Mexico by the 1970s. Decades of unregulated hunting and targeted trapping by the federal government to protect livestock took their toll.

By 1977, there were only seven known remaining Mexican gray wolves in the two countries.

Wildlife officials returned the subspecies to the wild in 1998 and, after decades of management, at least 241 Mexican gray wolves now roam New Mexico and Arizona, according to the Fish and Wildlife Service.

The federal agency imposed the boundary along I-40, which cuts across the Southwest, in part because the documented historical range of the subspecies did not extend north of the interstate. Officials also faced pressure from ranching and hunting interests to restrict the recovery area.

But the wild population has a lack of genetic diversity.

Each wild Mexican gray wolf’s genes are as similar to the next as siblings’ genes would be, said Michael Robinson, a senior conservation advocate at the Center for Biological Diversity and the author of a book on wolf management.

Instead of creating a wolfless buffer zone, Smith and Robinson said, wildlife managers should introduce Mexican gray wolves into southwestern Colorado.

Those wolves then would breed with northern gray wolves and add much-needed genetic diversity to the subspecies, while minimizing the risk of the northern species’ genes taking over the Mexican gray wolf population. The risk to the Mexican gray wolf would be greater if northern gray wolves established themselves farther south in the core of the Mexican gray wolf’s habitat.

“We can try to approximate the gradation of wolf types that (once) existed from north to south,” Robinson said.

Wandering under watch

The technical working group that shaped Colorado’s wolf reintroduction plan considered reintroducing Mexican gray wolves here but found them the “least desirable” option.

The ballot measure that mandated Colorado’s reintroduction of wolves did not specify whether a subspecies could be reintroduced. But the group wrote in its final report that the Mexican gray wolf should be the lowest priority for reintroduction because Colorado was not part of its historical range. It also cited logistical management concerns due to the subspecies being managed separately under the Endangered Species Act.

“Because they are listed as a unique entity under the ESA, maintaining the genetic uniqueness of this subspecies is paramount,” the November 2021 report states. “If Mexican wolves were present in Colorado, premature interbreeding with wolves from the north could compromise the Mexican wolf recovery effort.”

It’s unlikely that Mexican gray wolves roamed in Colorado before their extirpation, but the subspecies is better adapted than the northern gray wolf to warmer, drier climates — which is the expected future for southwest Colorado as the climate shifts, Smith said.

“We have to recognize that we’re imposing not just political boundaries, but also pretty complicated legal frameworks on wildlife that do whatever they want on a landscape,” he said. “It’s a problem that we’ve painted ourselves into.”

Biologists have said that Mexican gray wolves need at least three separate but connected populations to thrive, Robinson noted. One study found that one of those populations should be located in southwest Colorado.

It would have made sense to keep the Mexican gray wolves separate when there were only a few dozen of them, Robinson said. But the population is now robust enough to allow some northern gray wolf genetics into the pack, he said.

While all of Colorado’s 12 current wolves — including two that predated the reintroduction effort — and the wolves released in the state in coming years will have radio collars, their progeny will not. That will make tracking whether the wolves have moved into neighboring states more difficult, Odell said.

“It’s not in perpetuity,” Odell said of the agreements with the other states. “We’ll revisit this in time and see how things are going.”

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