Scientists Found an Animal That Walks on Three Limbs. It’s a Parrot.

Small parrots with bright rainbow colors are popular pets. They swing from ropes, cuddle with companions, and race for treats in a waddling gait with toddlers who spot a cookie. Along with other parrots, they use their faces to climb walls.

These birds will cycle between their left foot, right foot and beak if they are given a vertical surface to climb on. A new analysis of the forces climbing lovebirds exert shows that this is exactly what they are doing. A team of scientists wrote in the journal Proceedings of the Royal Society B that the birds and other parrot species have adapted their muscles in their neck and heads to walk on their beaks.

Michael Granatosky, an assistant professor of anatomy at the New York Institute of Technology and an author of the new paper, said that climbing with a beak as a third limb is not something life on Earth is capable of producing.

He said that everything is bilateral in the animal kingdom. It is unlikely to grow an odd number of limbs for walking.

Some animals have found ways to work around things. When hopping slowly, gannets use their tails as a fifth limb, pushing off from the ground with their hind legs the same way they push with their feet.

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The lovebirds were brought into the lab to see if parrots were using their beaks in the same way. They had the birds climb up a surface that was fitted with a sensor to keep track of how much force they were using. The scientists found that the propulsive force the birds applied through their beaks was similar to what they provided with their legs. The way to eat had turned into a way to walk, with beaks as powerful as their limbs.

Ms. Young said that the birds would have had to change their nervous systems to fit beak movement into the rhythm of walking.

Dr. Granatosky thinks that parrots may have evolved this ability because they can't hop up and down the trunks of trees. The parrots alternate their legs when they walk. They had to come up with something different, something that would give them the third limb that developmental biology couldn't provide them.

How often parrots walk in their daily lives is one of the questions the researchers have. The green monk parakeets live in the Gothic Revival-style gate of Green-Wood Cemetery in Brooklyn and Dr. Granatosky wants to know what role it plays in their behavior.

He hopes that the lovebirds and monk parakeets will help illuminate how parrots evolved such an unusual way of climbing and what changes they made to their bodies to do it.