The discovery of a bald eagle and loon chick dead in Highland Lake in Bridgton, Maine last summer prompted wildlife biologists to launch an investigation resembling a Sherlock Holmes mystery—if all the suspects and victims were replaced by birds.
A necropsy determined that the eagle had a puncture wound extending into the animal’s heart the size of an adult loon’s beak. In turn, the loon chick had sustained injuries that matched to an eagle’s talons, according to wildlife biologist Daniel D’Auria, who wrote a blog post for the Maine Department of Inland Fisheries and Wildlife. The verdict: an adult loon had stabbed and killed the bald eagle in an attempt to protect its chick from attack, making this the first documented case of a loon killing a bald eagle.
Both male and female loons are highly territorial, says Charlie Walcott, professor emeritus of neurobiology and behaviour at Cornell University, and former Director of the Cornell Lab of Ornithology. They don’t stand for intruders and will duke it out with other loons that intrude on their space. These battles aren’t for the faint of heart; loons will deliver a fatal blow by swimming up underneath their opponent and spearing them through the sternum, beak-first. “Of the male battles, about thirty percent are fatal. It is almost always due to a puncture-wound stabbing from below,” says Walcott.
It appears that this common loon-on-loon method of attack was used by one of the chick’s parents against the bald eagle. “My guess is that the eagle was down very close to the water, grabbing this chick, and the adult was able to get in and treat it as if were another loon,” says Walcott.
Loons typically have a clutch of two eggs, says Walcott. Their preferred nesting habitat are small islands on a lake, where it is more difficult for raccoons and other mammal predators to prey on the eggs. The young loons take to water very quickly, and the parents continue to feed and protect the babies from predators until the adult loons leave the young on their own to migrate in the fall. The offspring eventually move on to a staging area before migrating south themselves for the winter.
This now-solved murder mystery case shows the importance of having scientists in the field to understand the interactions between species, like loons and bald eagles. Another prime example occurred when Walcott began working on loons, and he visited the Seney National Wildlife Refuge in Michigan’s Upper Peninsula, home to a population of banded loons. At the time, the refuge manager didn’t think that bald eagles were a predator of adult loons. The following winter, Walcott received a telephone call from the refuge manager. “‘We just looked in the eagle’s nest,’” he recalled hearing, “‘and it is full of loon bands.’”