ALBUQUERQUE — A federal judge has rejected the final part of a challenge by environmental groups to a U.S. Fish and Wildlife Service decision to designate the northern aplomado falcon as a nonessential, experimental population in New Mexico and Arizona.

The environmentalists alleged the designation violated federal policy and stripped the falcon of needed protections under the Endangered Species Act. They wanted U.S. District Judge William Johnson to declare the designation illegal and force the Fish and Wildlife Service to respond to their petition for critical habitat in Texas, New Mexico and Arizona.

Johnson's legal opinion Tuesday upheld the federal agency's determination that there was no native population of falcons in New Mexico before a 2006 program to release them in the state.

The program has released about 120 birds since its inception.

The judge rejected the environmentalists' contention that New Mexico fell within the species' current range and that New Mexico's population was not "wholly separate geographically" from nonexperimental populations across northern Mexico or those released in West Texas.

He said Fish and Wildlife's interpretation did not conflict with the Endangered Species Act.

"The court supported us on everything," said Elizabeth Slown, a spokeswoman for Fish and Wildlife in Albuquerque. That means the reintroduction program can continue, she said.

Even though the government and environmental groups were in court, they were fighting for the same goal — the recovery of the northern aplomado falcon, Slown said.

"Our disagreement was with how we were going to recover it," she said. "We're pleased that the court supported us all the way."

Environmentalists are disappointed by the judge's ruling, said Nicole Rosmarino, wildlife program director for WildEarth Guardians, one of several groups that sued over the falcon two years ago. WildEarth Guardians has not decided whether to appeal, she said.

"We think there was overwhelming evidence of wild falcons in this state, and those wild falcons were denied protections by the Fish and Wildlife Service and now by Judge Johnson," Rosmarino said.

Slown said nonessential populations still are protected by the Endangered Species Act. Fish and Wildlife uses the designation in returning a species to its former habitat because that gives the agency "flexibility on how we're going to do it," she said.

The environmental groups sued the Fish and Wildlife Service and The Peregrine Fund in 2006, the year the federal agency designated the falcons an experimental population in New Mexico and Arizona. The designation cleared the way for The Peregrine Fund to begin releasing captive-bred falcons in Southern New Mexico.

Environmentalists argued that reintroduced animals can be designated experimental only if they're outside a species' current range. They contended New Mexico already had aplomado falcons because there were more than two dozen sightings in the two years before the first 11 birds were released in August 2006 under reintroduction.

Government attorneys, however, argued that sporadic sightings in New Mexico didn't mean there was a breeding population.

In late May, Johnson denied environmentalists' claims that the agency violated the Endangered Species Act by not responding to their petition within a set period and that it did not rely on the best science in designating the New Mexico and Arizona populations as experimental.

However, he agreed with the environmentalists' argument that Fish and Wildlife unreasonably delayed action on critical habitat for the bird in Texas. He stressed his decision meant only that Fish and Wildlife had to answer the groups' petition within 30 days.

Rosmarino said the agency has since told WildEarth Guardians it does not plan to designate critical habitat in Texas. She said the group was considering appealing that decision because of degradation of important falcon habitat at national wildlife refuges in that state.