They wouldn't blow away the competition on "Dancing with the Stars," but it turns out that some birds got rhythm.

After studying a cockatoo that grooves to the Backstreet Boys and about 1,000 YouTube videos, scientists say they've documented for the first time that some animals "dance" to a musical beat.

The results support a theory for why the human brain is wired for dancing.

In lab studies of two parrots and close review of the YouTube videos, scientists looked for signs that animals were actually feeling the beat of music they heard.

The verdict: Some parrots did, and maybe an occasional elephant.

But researchers found no evidence of that for dogs and cats, despite long exposure to people and music, nor for chimps, our closest living relatives.

• Click here to watch Snowball dance.

• Click here to watch other parrots do it too.

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Why? The truly boppin' animals shared with people some ability to mimic sounds they hear, the researchers say. (Even elephants can do that).

The brain circuitry for that ability lets people learn to talk, and evidently also to dance or tap their toes to music, suggests Aniruddh Patel of The Neurosciences Institute in San Diego. He proposed the music connection in 2006.

He also led a study of Snowball that was published online Thursday by the journal Current Biology.

A separate YouTube study, also published Thursday by the journal, was led by Adena Schachner, a graduate student in psychology at Harvard.

In sum, the new research "definitely gives us a bit of insight into why and how humans became able to dance," Schachner said.

A video of Snowball bobbing his head and kicking like a little Rockette to music has been viewed more than 2 million times on YouTube since it was posted in 2007. Patel saw it after a colleague pointed it out.

"I was very impressed," Patel said.

So he collaborated with Snowball's owner in Indiana for a more formal test. That showed Snowball wasn't just mimicking the movements of somebody off-camera.

And Snowball's movements followed the beat of his favorite Backstreet Boys song, "Everybody (Backstreet's Back)" even when researchers sped up the tune and slowed it down.

Actually, Snowball drifted in and out of following the beat, just as a child does, Patel said. But statistical analysis of his head bobs showed they really were related to the tempo.

Schachner and colleagues, meanwhile, found that videos of Snowball passed their own tests for following a beat.

They also tested an African gray parrot named Alex, whose mental abilities had been studied for many years, earning him a measure of scientific fame, but who hadn't been trained to respond to music.

"We had no idea he would do anything in response to the musical beat," Schachner said. But when the music started, "to our surprise, Alex started to dance."

Analysis showed Alex's head bobbing tracked the musical beat.

(Alex died in 2007, shortly after the study. He starred in a recent book, "Alex & Me," by researcher Irene Pepperberg, a co-author of Schachner's paper).

To cast a wider net in the animal kingdom, Schachner and colleagues searched YouTube for videos of dancing animals.

Out of about 1,000 such videos, they found 49 that appeared worthy of a detailed analysis; 33 videos showed convincing evidence of animals following a musical beat.

Those animals were 14 species of parrot and one species of elephant — all known to be able to mimic sounds they hear, a result that supports Patel's theory.

Schachner, who pointed out that elephants are often trained performers and that little is known about the elephant videos, said it will take further work before she's convinced that elephants really move to a beat on their own.

When researchers contacted the owners of some parrots in the videos, they were told that the birds' response to music had been a surprise, indicating a natural ability.

Still, not every parrot will dance to music, and so the brain circuitry for so-called "vocal mimicry" apparently isn't enough by itself to make an animal boogie, Schachner said.

In a Current Biology commentary, W. Tecumseh Fitch of the University of St. Andrews in Scotland said the new work topples the claim that only people can move to a musical beat.

It would make sense to study dolphins for that ability, and it's too early to rule out apes, he said.