“We’re working hard to have this done by the end of the year and I’d say it’s very imminent,” Aurelia Skipwith told The Associated Press on Monday.

The administration also is pushing ahead with a rollback of protections for migratory birds despite a recent setback in federal court, she said.

The Fish and Wildlife Service last year proposed dropping the wolf from the endangered list in the lower 48 states, exempting a small population of Mexican wolves in the Southwest. It was the latest of numerous attempts to return management authority to the states - moves that courts have repeatedly rejected after opponents filed lawsuits.

Shot, trapped and poisoned to near extinction in the last century, wolves in recent decades rebounded in the western Great Lakes region and portions of the West, the total population exceeding 6,000. They have been removed from the endangered list in Montana, Idaho, Wyoming and portions of Oregon, Utah and Washington state.

Federal protections remain elsewhere. A federal judge in 2014 restored protection for the animals in Michigan, Minnesota and Wisconsin, a decision upheld by an appeals court in 2017.

Director Skipwith, echoing the Fish and Wildlife Service’s long-held policy, told the AP the wolf has “biologically recovered” and that its removal from the list would demonstrate the effectiveness of the Endangered Species Act.

But the Humane Society of the United States and other wildlife protection groups contend wolves are still vulnerable. Dropping protections across the Lower 48 would doom any chances of their spreading to other states where they could thrive if humans allowed it, they say.

A final decision had been expected last spring, but the service is taking extra time to review the science behind its position and issues raised in court rulings, Ms Skipwith said.

“We just want to be sure we’re covering all the bases,” she said. “When groups want to come in and sue because of such a success, it takes away resources from species that need them.”

She added that the agency doesn’t believe much suitable habitat remains beyond areas that wolves currently occupy, a claim that environmental groups and some biologists dispute.

“We don’t anticipate them expanding, regardless of that federal protection,” Ms Skipwith said, declining to take a position on a November ballot initiative that would restore wolves to Colorado.

“If that’s the approach that Colorado wants to take, that’s their prerogative,” she said.

Ms Skipwith said the agency also is proceeding with changes in how it enforces a century-old law protecting most American wild bird species, despite warnings that billions of birds could die as a result.

A US judge in New York this month invalidated the administration’s use of a legal memo to justify its position that accidental but foreseeable killing of birds should not be criminally prosecuted. The administration had argued that the Migratory Bird Treaty Act applies only to the intentional killing of birds and not “incidental” killings during normal activities by electric utilities, oil developers and other industries.

National Audubon Society chief conservation officer Sarah Greenberger criticised the agency for pressing ahead with a rule change that would cement the policy into a regulation that could be harder to overturn.

“There was never a good reason to weaken the Migratory Bird Treaty Act and the administration should have taken its recent loss in court as an opportunity to abandon its bird-killing policy,” Ms Greenberger said.

Director Skipwith said the Fish and Wildlife Service was still evaluating the judge’s decision and planned to issue a final rule by the end of the year. The agency remains committed to “making sure we’re not criminalizing these unintentional actions” while stepping up efforts to protect migratory birds, she said.

The Endangered Species Act has protected at-risk species for more than 40 years and has been credited with saving species like the bald eagle, along with the gray wolf. More than 90 per cent of voters support the Endangered Species Act, according to a 2015 poll, across party lines.