Alastair Rae via Wikimedia Commons // CC BY-SA 2.0
Alastair Rae via Wikimedia Commons // CC BY-SA 2.0

Why Are Some Birds So Smart? Their Brains Are Neurally Dense

Alastair Rae via Wikimedia Commons // CC BY-SA 2.0
Alastair Rae via Wikimedia Commons // CC BY-SA 2.0

Little by little, the well-established myth of the stupid bird is crumbling. Just a few months ago, researchers reported that some birds are as smart as apes. Now another team of scientists say that bird brains pack way more brain cells per square inch than those of primates and other mammals. They published their findings in the Proceedings of the National Academy of Sciences.

The brains of humans and apes include a structure called the neocortex, which houses some of our most sophisticated thought processes and mental tasks. Birds don’t have neocortices at all, and so for years, scientists assumed that meant they were unintelligent. As it turns out, we were just being self-centered. Birds don’t need neocortices; a similar structure called a pallium does their mental heavy lifting.

One bird stereotype is accurate: Compared to, say, a human or a chimpanzee, birds do have little brains. Yet “corvids and some parrots are capable of cognitive feats comparable to those of great apes,” the authors write. “How do birds achieve impressive cognitive prowess with walnut-sized brains?”

To find out, the researchers examined the brains of 28 different bird species, from tiny zebra finches to towering emus. They examined the birds’ brain tissue at a cellular level, measuring the number and distribution of neurons in each region. They compared the neural density to that found in the brains of mice, rats, primates, and artiodactyls (even-toed ungulates).

As it turns out, when it comes to brain cell density, birds have them all beat. The pallium was crammed wall-to-wall with brain cells. Parrot and songbird brains contained twice as many neurons as similar-sized primate brains, and two to four times as many neurons as those of rodents. Birds also dedicate way more brainpower to their pallia than we do to our neocortices. The pallium houses 33 to 55 percent of a songbird’s brain cells, and 46 to 61 percent of a parrot’s. By comparison, the human neocortex hosts only 19 percent of our brain cells.

Senior author Suzana Herculano-Houzel, a neuroscientist at Vanderbilt University, said in a press statement: “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, and in birds we find that nature has used both of them.”

These findings open a new pathway in understanding how brains evolve. Generally speaking, in order to advance, brains have had to get bigger, and bigger brains are linked to more cognitive capacity. But, Herculano-Houzel said, “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."

But no evolutionary advantage is truly free. Does a denser bird brain require more energy to run than ours, which are spacious by comparison? If so, where is that energy coming from?

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

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Jana Mueller
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Animals
Ravens Can Figure Out When Someone Is Spying on Them
Jana Mueller
Jana Mueller

Corvids, the family of birds that includes crows and ravens, are canny beasts. They've been known to exercise self-control, count, hold grudges, and more. Now, new research suggests they possess at least a rudimentary Theory of Mind—the ability to attribute mental states to others.

A study in Nature finds that ravens can tell when someone else can see them, guarding their food when a peephole to their cache is open. While previous research suggested that birds might have an awareness of other animals' mental states, the results have been inconclusive. The Nature study is evidence that corvids can do more than just track other birds' gaze; they may understand the concept of "seeing."

Vienna-based researchers set up two rooms separated by windows that could be closed with covers. These covers had peepholes in them that could also be opened or closed. First, the 10 ravens were each allowed to cache food, while other birds were in the next room and the windows were open or closed. Then, they were trained to look through the peepholes to find food in the other room, so that they knew that the holes could be used to see through the window covers. Afterwards, each of the ravens was again presented with food with one of the two peepholes open. The adjacent observation room didn't have any birds in it, but the researchers played the sounds of another raven recorded during one of the previous trials.

When the birds heard the sounds of another raven in the next room, and the peephole was open, the birds behaved as if they knew they were being watched—they hid their cache of food quickly and didn't add more food to it as often, as if they knew that it might be compromised. However, they behaved normally when the peephole was closed.

This suggests that ravens don't just track their competitors' gaze to know when they’re being watched, but can infer from past experience when they can be seen.

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Big Questions
Why Do Dogs Crouch Forward When They’re Playing?
iStock
iStock

Whether they're tilting their heads or exposing their bellies for rubs, dogs are experts at looking adorable. But these behaviors do more than elicit squeals from delighted humans; in many cases, they serve important evolutionary functions. A prime example is the "play bow": If you've ever seen a dog crouch forward with its elbows on the ground and its rear end in the air, wagging tail and all, then you know what it is. The position is the ultimate sign of playfulness, which is important for a species that often uses playtime as practice for attacking prey.

The play bow first evolved in canids as a form of communication. When a dog sees another dog it wants to play with, it extends its front paws forward and lifts up its behind as a visual invitation to engage in a friendly play session. Dogs will "bow" in the middle of playtime to show that they're having fun and wish to continue, or when a session has paused to signal they want to pick it back up. Play bows can also be a sort of apology: When the roughhousing gets too rough, a bow says, “I’m sorry I hurt you. Can we keep playing?”

Play between canines often mimics aggression, and starting off in a submissive position is a way for all participating parties to make sure they’re on the same page. It’s easy to see why such a cue would be useful; the more puzzling matter for researchers is why the ancestors of modern dogs evolved to play in the first place. One theory is that play is crucial to the social, cognitive, and physical development of puppies [PDF]. It’s an opportunity for them to interact with their own kind and learn important behaviors, like how to moderate the strength of their bites. Play also requires the animals to react quickly to new circumstances and assess complex actions from other dogs.

Shiba inus playing outside.
Taro the Shiba Inu, Flickr // CC BY 2.0

Another evolutionary explanation is that playtime prepares puppies for the hunting they do later as adults. Watch two puppies play and you’ll see them stalking, biting, and pouncing on one another—all behaviors canines exhibit in the wild when taking down prey.

Of course, it’s also possible that dogs simply play because it’s fun. This is a strong case for why pet dogs continue to play into adulthood. “Devoting a lot of time to play may be less advantageous for a wild species who spends much of its time hunting or foraging for food, searching for mates, or avoiding predators,” Dr. Emma Grigg, an animal behaviorist and co-author of The Science Behind a Happy Dog, tells Mental Floss. “Many domestic dogs are provisioned by humans, and so have more time and energy to devote to play as adults.”

Because play is a lifelong activity for domestic dogs, owners of dogs of all ages have likely seen the play bow in person. Wild canids, like wolves, foxes, and coyotes, tend to reserve this behavior for members of their own species, but pet dogs often break out the bow for their humans—or anyone else who looks like they might be up for a play session. Grigg says, “One of my dogs regularly play bows to her favorite of our cats.”

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