Size matters.

Maybe it’s time we toss that little put-down out the window, a new study released Tuesday says.

Here’s why: The brain of a macaw, about the size of a walnut, is much smaller than the lemon-sized brain of a macaque, but the bird is probably more intelligent than the primate. The part of the brain associated with intelligent behavior is front-loaded with far more neurons in the tiny bird than the big, hairy mammal, the study says.

Birdbrain.

Toss out that insult, too, says the study’s senior author, Suzana Herculano-Houzel, a Vanderbilt University neuroscientist.

“For a long time having a ‘bird brain’ was considered to be a bad thing; now it turns out that it should be a compliment,” she said.

On the heels of an earlier study showing that trained pigeons can detect malignant tumors in mammograms with the pinpoint accuracy of human radiologists, Herculano-Houzel’s report published in the Proceedings of the National Academy of Sciences is another nod to the higher intelligence of birds. Recognition goes not only to the technicolor talking macaw, but also to the pint-sized zebra finch, the towering emu and more than 20 other birds.

Want to find a malignancy in a mammogram? Train a pigeon to do it.

For about a decade, humans, with their big brains, have been trying to figure out why birds with brains like garlic cloves “perform complicated cognitive behaviors,” said a statement released by Vanderbilt announcing the study.

Herculano-Houzel and her co-author, Pavel Nemec, a researcher at Charles University in Prague, used a brain measuring device called an isotropic fractionator to determine the number of neurons in specific regions of the brains of birds. They found that birds generally have more neurons than some mammals, but parrots and songbirds packed twice as many neurons on average than primate brains, “indicating that avian brains have higher neuron packing densities than mammalian brains,” the study said.

“Additionally, corvids and parrots have much higher proportions of brain neurons located in the pallial telencephalon,” a part of the brain that controls emotions, hearing, vision, personality and more. The authors imply that the high density of neurons in this area contributes to the basis of avian intelligence.

“We’ve been underestimating birds for a long time because people would look at their brains and say they have bird brains,” Herculano-Houzel said. “I certainly didn’t expect the finding that they would be packed with so many more neurons. That’s pretty incredible, but it’s real.”

The neurons could endow birds with better sensory abilities and motor skills. But other potential functions — reasoning and planning for the future, for example — are a mystery. “Sure you have a lot of neurons,” the authors asked, but what do they do?

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What isn’t a mystery is that size doesn’t always equal higher cognitive ability when it comes to brains. “In designing brains, nature has two parameters it can play with: the size and number of neurons and the distribution of neurons across different brain centers,” Herculano-Houzel said.

The authors note in the statement that the relationship between intelligence and neuron count has not been firmly established. The study’s importance is that it demonstrates that there are more ways to build large brains. In the past, neuroanatomists thought that brains had to be bigger to hold more and larger neurons.

“But bird brains show that there are other ways to add neurons: Keep most neurons small and locally connected and only allow a small percentage to grow large enough to make the longer connections. This keeps the average size of the neurons down,” she explained.

She said she hopes that these findings will lead to more studies on the cognitive processes of birds and fewer assumptions that they lack the brainpower of mammals. There are other questions that Herculano-Houzel will seek to answer in her next study: What is the cost to birds for having so much more brainpower than humans realized?

“If they really pack this many neurons in such small brains … and can only get so much food, that may be the reason birds are limited to a certain body size. They can’t get enough calories because of flight and the brains’ neurons,” she said. “It could actually pose such a burden on a species that they can only be so big. That’s something we have to investigate now.”