For the first time in decades, a radio-collared endangered Mexican wolf crossed from the U.S. into Mexico last week in New Mexico, a federal official said on Friday, but environmental groups warn the animal may never return due to U.S. border wall construction.

The male wolf crossed into Chihuahua, Mexico, from a remote area of the New Mexico Bootheel, according to Aislinn Maestas, a spokesperson for the U.S. Fish and Wildlife Service, which tracks members of the smallest and rarest subspecies of North American gray wolf, also known by its Spanish name "lobo."

Once common in the Southwestern U.S. and Mexico, the wolf came close to extinction in the 1970s, exterminated by government agencies and ranchers who claimed targeting the species would protect livestock.

The wolves have for millennia roamed the Bootheel's grasslands, desert and wooded mountains, traversing the migration corridor in search of prey and mates in what is now Mexico and the U.S.

The administrations of President Donald Trump and former President Joe Biden have built a steel border wall westward across New Mexico to stem the trafficking of migrants and drugs.

Current construction of the 18- to 30-foot-high barrier in the area means last week's wolf border-crossing may be the last ever by the species, conservationist Michael Robinson said on Friday.

That would exacerbate the wolf's chronic inbreeding, which has led to lower survival rates for pups, as well as cancers and birth defects.

“Sealing off the Bootheel would isolate wolves and other rare mammals like jaguars and ultimately make them all less likely to survive,” Robinson, a senior conservation advocate at the Center for Biological Diversity, said in an interview.

The Department of Homeland Security and its U.S. Customs and Border Protection agency, which are responsible for border wall construction, did not immediately respond to a request for comment.

DIVERSITY PROBLEM

Conservation groups and some U.S. wildlife officials have said expansion of the border wall will fragment habitats and disrupt migration routes in regions such as the Big Bend area of Texas, the San Rafael Valley of Arizona and the Otay Wilderness in California. The Department of Homeland Security has used legal authority to override environmental laws, leading to lawsuits against barriers.

U.S. administrations from both parties have acknowledged environmental risks but argue the barrier is necessary for national security. Officials have incorporated mitigation features like ground-level wildlife openings for small animals such as reptiles and rodents.

In the case of the Mexican wolf, mating between animals from the U.S. and Mexico could increase critically low genetic diversity, said Cyndi Tuell, Arizona and New Mexico director at Western Watersheds Project, a conservation group.

All modern Mexican wolves are descended from just seven wolves that were successfully bred after being captured as part of a binational breeding program started in the late 1970s.

As of this year there are at least 319 wild Mexican wolves in the U.S., around 36 in Mexico and about 380 in captive breeding programs, according to USFWS and conservation groups.

-Andrew Hay/Reuters