Death takes many forms for the red squirrels of the Yukon: Birds of prey strike from above while silent lynx stalk the snows below. And sometimes, red squirrels slay their own.

In a study published this week in The Scientific Naturalist, researchers report that North American red squirrel pups often fall victim to attacks from nearby males. Sometimes these murderous males also eat the youngsters they kill.

The first time Haines saw this grisly behavior was in 2014. A male squirrel she knew on sight—each is marked with bits of colored wire on the ear—ran up a tree to a female’s nest and sunk his teeth into a pup, which fell through the branches and died. A week later, Haines found