Scientists found an animal that walks on three limbs. It’s a parrot.

Lovebirds are popular pets. The colorful parrots swing from ropes, cuddle with companions and race for treats in a waddling gait with all the urgency of toddlers who spot a cookie. But they also do something strange: They use their faces to climb walls.

Give these birds a vertical surface to clamber up, and they cycle between left foot, right foot and beak as if their mouths were another limb. In fact, a new analysis of the forces climbing lovebirds exert reveals that this is precisely what they are doing. Somehow, a team of scientists wrote in the journal Proceedings of the Royal Society B on May 17, the birds have repurposed the muscles in their necks and heads so they can walk on their beaks, using them the way rock climbers use their arms.

Climbing with a beak as a third limb is peculiar because third limbs generally are not something life is capable of producing, said Michael Granatosky, an assistant professor of anatomy at the New York Institute of Technology and an author of the new paper.

“There is this very deep, deepset aspect of our biology that everything is bilateral” in much of the animal kingdom, he said. The situation makes it developmentally unlikely to grow an odd numbers of limbs for walking.

Some animals have developed workarounds. Kangaroos use their tails as a fifth limb when hopping slowly.

To see if parrots were using their beaks in a similar way, Granatosky and a graduate student, Melody Young, as well as colleagues brought six lovebirds from a pet store into the lab. They had the birds climb up a surface that was fitted with a sensor to keep track of how much force they were exerting and in what directions. The scientists found that the propulsive force the birds applied through their beaks was similar to what they provided with their legs. What had started as a way to eat had transformed into a way to walk.

Granatosky speculates parrots may have evolved this ability because they cannot hop up and down the trunks of trees. Parrots alternate their legs when they walk, rather than pushing off with both legs at once. So when it came to moving vertically, they had to come up with something that created the third limb.

How often parrots do this three-limbed walking is another question researchers have.