The macaw has a brain the size of an unshelled walnut, while the macaque monkey has a brain about the size of a lemon. Nevertheless, the macaw has more neurons in its forebrain – the portion of the brain associated with intelligent behavior – than the macaque. That is one of the surprising results of the first study to systematically measure 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, which found that they consistently have more neurons packed into their small brains than are stuffed into mammalian or even primate brains of the same mass. The study results were published online in a paper titled “Birds have primate-like numbers of neurons in the forebrain” in the Proceedings of the National Academy of Sciences early edition on the week of June 13. “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,” said Vanderbilt University neuroscientist Suzana Herculano-Houzel, senior author of the paper with Pavel Němec at the Charles University in Prague. The study provides a straightforward answer to a puzzle that comparative neuroanatomists have been wrestling with for more than a decade: how can birds with their small brains perform complicated cognitive behaviors?