A bear had been asleep in a strange place. It was the nest of an eagle with a bald head. Researchers spotted the sleeping bear as they surveyed nests of eagles at the military base in Alaska.

Black bears ( Ursus americanus) are sometimes observed to take benefit of the eagles’ architectonic work. These incursions can cause trouble for birds as well as their young, according to the U.S. Fish and Wildlife Service (FWS).

“In the past, a few eagle nests have been raided by black bears with predictably bad results for the nesting eagles,” FWS staff wrote in a post on Facebook on the 21st of July, stating that such incidents usually cause young birds to go missing.

Bears are known to devour eagles’ eggs as well as nestlings, according to Stephen B. Lewis, an FWS animal biologist who conducted the nest surveys at JBER, a Joint Base Elmendorf Richardson (JBER) the military’s base located in the southern part of Alaska. “It’s hard to say how much bears invade eagle nests because we don’t (can’t) spend that much time monitoring to see it happen or have cameras to witness it,” Lewis said to Live Science in an email.

In a helicopter inspection in May, researchers observed a female bald eagle ( Haliaeetus leucocephalus) with an egg incubating within the nest. A sleeping bear later occupied the nest. After a week, the egg was put out in the cold as the female eagle and her mate sat around.

“It wasn’t clear if the nesting attempt had failed or if the female was just taking a break from incubating,” Lewis explained, pointing out that males typically take over from females to keep the eggs warm, especially in cold areas such as Alaska. Lewis believes it was a ” failed ” case in the spring, even before the bear swam into it.

Bald eagles are Alaska’s most enormous resident birds of prey. They have about 7.5 feet (2.3 meters) of wingspans per the ADFG. They build the most massive nests in the history of North American birds, with some nests that measure 8 feet (2.4 meters) in length and weigh more than 2 tonnes (1.8 tons in metric tonnage).

The vast nests can offer safe places to rest for bears, which usually build “beds” on very steep slopes so that other animals don’t interfere with the bears, Lewis said. “This nest isn’t that far off from such a bear bed. It could have just happened to climb the tree and decided to take a nap.”

The smell of fishy scents emanating from the nest could be why the bear was lured by it. Eagles’ nests are “rather smelly,” because the fish they catch to feed their children are often left unattended. “Often that food isn’t entirely consumed and ends up getting stomped into the nest or laying on the side and rotting,” Lewis explained. “Bears have incredible senses of smell so perhaps a bear is attracted to the smelly nest.”

Bald eagles were classified as endangered across the U.S. in 1978 because their numbers had plummeted because of the destruction of habitats and illegal shooting, pesticides, and poisoning, in the words of the Alaska Department of Fish and Game (ADFG). More robust protections have allowed populations to recover, and monitoring continues to evaluate the impact of human-caused disturbances, like oil spills and tourism.