The Center for Biological Diversity is threatening to take legal action to protect rare seabirds that it says are being harmed by bright lights at an Air Force radar facility in Kokee, Kauai.

But the Air Force says it has turned off those external lights and taken other steps to protect Newell’s shearwaters and endangered Hawaiian petrels after numerous birds crashed onto the station’s property high in the mountains on foggy days in September.

The seabirds are attracted to artificial lights and get confused, circling around and colliding with things or falling exhausted to the ground. Known as ‘a‘o in Hawaiian, the shearwaters are a threatened species whose main breeding grounds are on Kauai’s mountains. The reflection of the moon and stars on the water helps guide them to the ocean.

The center on Tuesday sent a formal notice of intent to sue the U.S. Department of Defense, the Air Force and Kokee Air Force Station if they do not take action to correct what it described as violations of the Endangered Species Act.

The national nonprofit hopes to reach an agreement without having to file a lawsuit, said Brett Hartl, the center’s endangered species policy director. The law requires it to provide 60 days’ notice before suing.

The Kokee station was responsible for close to half of the shearwaters that “fell out” or crashed to the ground islandwide on Kauai last year, Hartl said in an interview. More than a dozen Newell’s shearwaters died and more than 100 were injured in September, along with six Hawaiian petrels, he said.

“That’s a huge blow to the species,” he said. “The base’s slow response and careless actions have significantly set back the recovery of these two species. They need immediate action to permanently protect them from this unnecessary risk.”

Because the shearwaters were breeding adults, their chicks might also have suffered from neglect, he said. Another shearwater crashed to the ground at the station on May 9, he said.

Col. Frank Flores, commander of the Pacific Air Forces Regional Support Center, said the military has taken action in collaboration with the U.S. Fish & Wildlife Service to protect the birds and continues to do so.

“We had a significant number of takes (downed birds) back in 2015, and in response to that we’ve turned the lights off after coordination with U.S. Fish & Wildlife,” he said Wednesday in a phone interview from his headquarters in Anchorage, Alaska.

“They’ve asked us to keep the lights off from April through December,” he added. “We agreed to turn the lights off and we are looking at ways to still provide adequate lighting to maintain the security of the station and protect the birds.”

Flores said the radar station plays a crucial role in providing signals for air defense and the many airliners that fly in and out of Hawaii.

“It is an extremely important site and one that we need to keep secure,” he said. “It’s a small installation with a few facilities but it is extremely critical to the state and to the region.”

The Kokee station, maintained by Hawaii Air National Guard personnel with about a dozen people on-site, falls under the jurisdiction of the 11th Air Force in Alaska.

Flores said the military has contracted with the University of Hawaii and others to supplement its own biologists to monitor and mitigate any effects on wildlife.

Since 2010, Kauai’s high school football teams have had to limit nighttime games in deference to the shearwaters, which are attracted to the stadium lights.

The Center for Biological Diversity, which has a million members nationwide, filed a notice of intent to sue the St. Regis Princeville Resort and Kauai Island Utility Cooperative in 2010 over their lights. The hotel altered its lighting. The utility received a permit in 2011 from the U.S. Fish & Wildlife Service that required it to reduce harm to the birds.

Shearwaters have a glossy black top and white underside, with wingspans of 30 or more inches. They nest in burrows on mountain slopes and ridgelines.