The term “bird brain” often implies less than average cognitive abilities. But that phrase is actually a misnomer, a new study suggests.

Researchers from the Czech Republic, Austria, and Brazil systematically measured the number of neurons in the brains of more than two dozen species of birds, ranging in size from the tiny zebra finch to the six-foot-tall emu, and discovered that birds have more neurons packed into their small brains than are stuffed into mammalian or even primate brains of the same mass.

The study was published on May 13 in the Proceedings of the National Academy of Sciences.

"We found that birds, especially songbirds and parrots, have surprisingly large numbers of neurons in their pallium: the part of the brain that corresponds to the cerebral cortex, which supports higher cognition functions such as planning for the future or finding patterns. That explains why they exhibit levels of cognition at least as complex as primates," said Suzanna Herculano-Houzel, PhD, one of the study authors, and now with Vanderbilt University.

That is possible because the neurons in avian brains are much smaller and more densely packed than those in mammalian brains, the study found. Parrot and songbird brains, for example, contain about twice as many neurons as primate brains of the same mass and two to four times as many neurons as equivalent rodent brains.

Not only are neurons packed into the brains of parrots and crows at a much higher density than in primate brains. The proportion of neurons in the forebrain is also significantly higher, the study found.