Research gives new meaning to the term 'bird brain'

Study gives new meaning to the term 'bird brain'
Graphic abstract illustrates the results of the study of the number of neurons in avian brains. Credit: Pavel Nemec, Charles University at Prague

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?

Study gives new meaning to the term 'bird brain'
The collection of avian brains that the scientists analyzed. For each species, the total number of neurons (in millions) in their brains is shown in yellow, the number of neurons (in millions) in their forebrains (pallium) is shown in blue and their brain mass (in grams) is shown in red. The scale bar in the lower right is 10 mm. Credit: Suzana Herculano-Houzel, Vanderbilt University

The conundrum was created by a series of studies beginning in the previous decade that directly compared the cognitive abilities of parrots and crows with those of primates. The studies found that the birds could manufacture and use tools, use insight to solve problems, make inferences about cause-effect relationships, recognize themselves in a mirror and plan for future needs, among other cognitive skills previously considered the exclusive domain of primates.

Scientists were left with a generally unsatisfactory fallback position: Avian brains must simply be wired in a completely different fashion from primate brains. Two years ago, even this hypothesis was knocked down by a detailed study of pigeon brains, which concluded that they are, in fact, organized along quite similar lines to those of primates.

The new study provides a more plausible explanation: Birds can perform these complex behaviors because birds' forebrains contain a lot more neurons than any one had previously thought - as many as in mid-sized primates.

"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 Herculano-Houzel, who recently joined the Vanderbilt psychology department.

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.

Credit: Vanderbilt University

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

"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," said Herculano-Houzel, "and in birds we find that nature has used both of them."

Although she acknowledges that the relationship between intelligence and neuron count has not yet been firmly established, Herculano-Houzel and her colleagues argue that avian brains with the same or greater forebrain neuron counts than primates with much larger brains can potentially provide the birds with much higher "cognitive power" per pound than mammals.

One of the important implications of the study, the neuroscientist said, is that it demonstrates that there is more than one way to build larger brains. Previously, neuroanatomists thought that as brains grew larger neurons had to grow bigger as well because they had to connect over longer distances. "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.

"Something I love about science is that when you answer one question, it raises a number of new questions," said Herculano-Houzel.

Credit: Vanderbilt University

Among the questions that this study raises are whether the surprisingly large number of neurons in bird brains comes at a correspondingly large energetic cost, and whether the small neurons in bird brains are a response to selection for small body size due to flight, or possibly the ancestral way of adding neurons to the brain - from which mammals, not , may have diverged.

Herculano-Houzel hopes that the results of the study and the questions it raises will stimulate other neuroscientists to begin exploring the mysteries of the avian brain, especially how their behavior compares to that of mammals of similar numbers of or size.

Explore further

Brain folding related to surface area and thickness, not number of neurons

More information: Birds have primate-like numbers of neurons in the forebrain, PNAS,
Citation: Research gives new meaning to the term 'bird brain' (2016, June 13) retrieved 24 July 2019 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Jun 13, 2016
Can someone make parrots say as many Alphabet letters as possible?
Let them say single letters to start with and then say 5 letters at a time together rhythmically.
Turn on Continuous/Repetitive Audio (Preferably a Female Voice) in its Cage until it succumbs and starts saying it.
Also, Keep providing a nut at a time whenever it says it.

Jun 13, 2016
"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," said Herculano-Houzel, "and in birds we find that nature has used both of them."

Let's see,

1. Size
2. Number
3. Distribution

I come up with three parameters.

Funny how an article where someone is claiming to have precisely counted something very difficult to count would leave you questioning the counter's abilities!

Jun 14, 2016
@be: "Genius parrot know the English Alphabet" https://www.youtu...waj6kr6U [with the potential of the handler giving involuntary signs].

@dan: I think she is thinking of number given by a certain size in a set skull volume. The context is poorly described though.

But it is an interview, and more mistakes than slips through peer review should be expected.

Jun 14, 2016
On the other hand, we have a bird-brained finch that has built its nest in a planter on our front porch --- under the patient and appreciative gaze of our cat. Two years in a row. Bird builds nest, cat eats eggs. Brilliant!

Jun 14, 2016
When I was about 9 years old I saved a young Robin from the hands of another kid and took it home to my mom who always loved birds. We took it into our home fed it and raised it to adulthood. We named it "Freckles". During its upbringing, my mom would dig in the flower garden it find worms and Freckles easily learned how to fend for himself. He would follow my mom from back yard to front yard and land on her hand or shoulder. After its child hood indoors it moved outdoors to a cage that was placed high on a trellis in our back yard. One day Freckles flew away and was not seen until the next year when my mom was tending to her garden. She saw two robbins sitting on the trellis. One robin flew to her and landed on her shoulder and sat for a brief period. Obviously, it was Freckles who came home to tell mom tha all was okay and that he had found a mate. Freckles returned to his mate on the trellis and then they both flew away, not to be seen again. A true Disney like story.

Jun 14, 2016
I wonder what the implications of this new found bird brain intelligence is for the intelligence of the dinosaurs?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more