BILLINGS, Montana: Researchers at Yellowstone National Park have lost their license for a set of radio frequencies used to track more than 100 radio-collared wolves and elk.

But park officials said on Thursday their scientific work has continued with the cooperation of the new license holder.

Yellowstone biologist Doug Smith said new licensee NorthWestern Energy is letting researchers share the frequencies, meaning the park can avoid more than $450,000 in estimated costs to restart the program.

Restarting the program would have required researchers to capture the wolves and elk already wearing collars and replace the devices with ones that operate on a different frequency.

The frequency license used by the park expired several years ago. It had been under the name of Ed Bangs, who led the US Fish and Wildlife Service effort to reintroduce wolves to the park in the 1990s. When Bangs retired in 2011, the license was never renewed, park officials said.

Interference began in radio signals from collared wildlife in September, after NorthWestern acquired the frequencies to improve communications for its own employees in the park and remotely control its power distribution network, according to Smith and the company.

The interference continued through the winter and into the spring, but researchers still could track the animals — roughly 30 wolves and 85 elk — from the air during monitoring flights, Smith said.

Park service emails obtained by the group Public Employees for Environmental Responsibility (PEER) show officials were concerned the loss of monitoring data would jeopardise years of science on wolves and the elk herds they hunt.

“It never stopped our research,” Smith said. “You’re listening for a beep and there’s a ton of static over it, but you can do it. It’s harder to do because you had to fly more and get closer to the animal.”

The executive director of PEER, based in Washington, D.C, said the radio frequency troubles suggest confusion among officials and researchers at a time when even remote areas such as Yellowstone are seeing increased congestion in airwaves.

“The park is giving approval to projects that may impede their ability to monitor wildlife,” Jeff Ruch said.

Park technology chief Bret De Young said that once park workers found out about the problem and discovered its source, they moved quickly to resolve it with NorthWestern. He said the company was gracious in accommodating the park’s needs.

Northwestern spokesman Butch Larcombe said the company was using those portions of its frequencies that interfere least with the wildlife collars. He said that would continue until the collars wear out and fall off the animals, which Smith said takes several years.

New collars in coming years will use new frequencies, under a 10-year license recently acquired by Smith.