ALBUQUERQUE, N.M. — On the edge of the Mogollon Rim in eastern Arizona, snow covered the ground and blizzard conditions were setting in as biologists prepared to open the gates to a trio of pens, releasing three packs of Mexican gray wolves that would soon have the distinction of being the first of their kind to roam the wild in decades.

Thursday marks the 20th anniversary of that release and a major milestone for an effort that started decades earlier when the predators were first declared an endangered species.

In the months following the 1998 release, five of the 11 wolves were poached and the remaining animals had to be captured and paired with new mates before being released again. The wild population has struggled to gain significant ground, and only recently reached a high of 114 wolves.

The costly effort to return Mexican wolves to the American Southwest and Mexico has been fraught with frustration, as ranchers push back over livestock kills by the predators and environmentalists warn of returning to the brink of extinction if more wolves aren’t released into the wild.

David Parsons, former coordinator of the Mexican wolf recovery program, said in an interview that the lack of progress is not the fault of the wolves.

“It’s really an issue of human tolerance and political will at this point to break through some of those barriers and allow the wolves to occupy the landscape at a level they would set themselves,” Parsons said. “We’re nowhere near that in terms of wolves having packs that fill up all the suitable wolf habitat out there.”

Members of Congress have weighed in along with governors, lawyers and scientists as governments and breeding facilities have spent tens of millions of dollars to recover the species.

For ranchers and others living along the Arizona-New Mexico border, there’s a feeling that the predators were forced upon them and that threats to their livelihoods and rural way of life have been ignored by the federal government.

“I can tell you had they tried harder to work with people up front, had they had the foresight to come up with some solutions ahead of time rather than just saying this is what we’re going to do and we’re going to do it, there may have been more acceptance,” said Caren Cowan, head of the New Mexico Cattle Growers’ Association, which represents about 1,400 ranchers.

“There’s just never been a good place for anybody to talk or come together. It’s just been at loggerheads since the absolute beginning,” she said.

Jamie Rappaport Clark, who led the U.S. Fish and Wildlife Service at the time of the 1998 release and had previously worked on the project while stationed in Albuquerque, acknowledged that lessons have been learned. She’s now president of the Washington, D.C.-based Defenders of Wildlife, which has been critical of how the wolf program has been managed and has tried to develop programs to minimize conflicts with the livestock industry.

“Wolves elicit all kinds of emotions in people. There’s a lot of hate, there’s fear, there’s all kinds of stuff and frankly I think we all could have done a better job at conditioning the landscape, at public education and more transparent collaboration,” she said.

Rappaport Clark defends the decision to release the wolves, saying the aim was to right a wrong.

The Mexican wolf once roamed portions of Arizona, New Mexico, Texas and Mexico. As the region became settled, wolves came into conflict with livestock. As a result of private, state and federal extermination campaigns, the wolf had been all but eliminated from the U.S. and Mexico by the 1970s.

Rappaport Clark said there was much excitement surrounding the 1998 release given that the agency had success returning gray wolves to Yellowstone just three years earlier.

But the Southwest was a different place, and biologists were dealing with captive-bred wolves rather than wild ones.

“That experiment was way bigger — a capital E experiment,” she said.

With lawsuits over management and recovery still pending, environmental groups plan to mark the anniversary of the initial release with screenings of a documentary at events in New Mexico and Arizona.

For Parsons, the release was unforgettable. He said the gates to the pens were opened just after sunset on March 29, 1998, a day earlier than planned because of the storm. The biologists spent the night in their canvas tents about a mile away. By morning, the wolves were out.