Scientists have figured out why parrots, one of the few animals that can imitate sounds and human speech, are "vocal learners."

Researchers at Duke University uncovered key structural differences in the brains of parrots, which had been unrecognized in studies published over the last 34 years, that explains the birds' unparalleled ability to imitate sounds and human speech.

Researchers have been trying to figure out why some bird species are better imitators than others. Besides differences in the sizes of particular brain regions, however, no other potential explanations have surfaced.

"This finding opens up a huge avenue of research in parrots, in trying to understand how parrots are processing the information necessary to copy novel sounds and what are the mechanisms that underlie imitation of human speech sounds," Mukta Chakraborty, a post-doctoral researcher in the lab of Erich Jarvis, said in a statement.

For the study, researchers examined gene expressions patterns and found that parrot brains are structured differently than the brains of songbirds and hummingbirds, which also exhibit vocal learning. In addition to having defined centers in the brain that control vocal learning called "cores," parrots have what the scientists call "shells," or outer rings, which are also involved in vocal learning.

They observed that the shells are relatively bigger in species of parrots that are well known for their ability to imitate human speech.

They found that most of the bird's vocal learning brain regions are tucked into areas that also control movement. These areas in parrots also show some special patterns of gene expression, which the scientists speculate might explain why some parrots are also able to learn to dance to music.

"It takes significant brain power to process auditory information and produce the movements necessary for mimicking sounds of another species," Chakraborty said. "The question is, how specialized are these parrot brains, and in what ways? Is it just a select group of specialized genes, or is it some specific projections that we haven't discovered yet?"

The findings are detailed in the journal PLOS One.