There Is An Animal Walking On Three Limbs. This is a Parrot.

Budgerigars, small parrots with vibrant rainbow plumage and cheeky personalities, are popular pets. They swing from ropes, cuddle with friends, and race for treats on a swinging walk with all the urgency of toddlers spotting a cookie. But they also do something strange with other parrots: They use their faces to climb walls.

Give these birds a vertical surface to climb on and their mouths will alternate between the left foot, right foot and beak like any other limb. In fact, a new analysis of the forces climbing budgerigars reveals that this is exactly what they are doing. Somehow, a team of scientists wrote Proceedings of the Royal Society B on WednesdayBirds, and perhaps other parrot species, have redesigned the muscles in their necks and heads so that they can walk on their beaks and use them in the same way that rock climbers use their arms.

Michael Granatosky, assistant professor of anatomy at the New York Institute of Technology and author of the new paper, said that climbing with the beak as a third limb is strange, as third limbs are usually not something life on Earth can produce.

“There’s a very deep, profound aspect of our biology where everything is two-sided,” he said of most of the animal kingdom. This makes it developmentally unlikely to grow an odd number of limbs for walking.

Some animals have developed workarounds. Kangaroos use their tails as their fifth limb as they jump slowly, pushing off the ground with their backs as they do with their feet.

To see if parrots use their beaks in a similar way, Dr. Granatosky and graduate student Melody Young and colleagues brought six pink-faced parakeets to the lab from a pet store. They had the birds climb a surface equipped with a sensor to track how much force and in what directions they were applying. The scientists found that the propulsion the birds exert from their beaks is similar to that they provide with their legs. What started as a way of eating had turned into a way of walking with beaks as strong as its limbs.

Noting that birds’ nervous systems need to change to match their beak movement to their walking rhythm, Ms. Young said, “It’s pretty incredible that they can take their faces and integrate them into their stride cycles.”

Dr. Granatosky speculates that parrots may have developed this ability because they cannot jump on tree trunks like woodpeckers and nuthatches. Instead of pushing with both legs at the same time, parrots switch legs as they walk. So when it came to the challenge of moving vertically, they needed to find something different, something that created the third limb that developmental biology couldn’t provide for them.

How often parrots perform this three-limb gait in their daily lives is another question on researchers’ minds. To understand how it plays a role in their behavior, Dr. Granatosky commissioned students to observe closely the green monk parakeets living in the tower. Gothic Revival-style gate of Green-Wood Cemetery in Brooklyn.

While the results have yet to be published, she hopes budgerigars and hermit parakeets will help illuminate how parrots developed such an unusual method of climbing and what changes they make to their bodies to do so.