Bird Brains

The complex life of birds.

My mom loved watching birds, as does my dad, and I’ve also come to appreciate the awesomeness evolution has packed into the small packages of birds.  Birds are everywhere, so it’s nice to appreciate what goes into them so you can even better appreciate something that’s all around you.

I recently read a pair of books on birds by Jennifer Ackerman, The Bird Way and The Genius of Birds, and this essay draws on her work.

Just watching birds in my backyard gather food, make nests, and communicate gives the lie to “bird brained” phrases people often use.  As Ackerman writes:

Our language reflects our disrespect [for birds]. Something worthless or unappealing is “for the birds.” An ineffectual politician is a “lame duck.” To “lay an egg” is to flub a performance. To be “henpecked” is to be harassed with persistent nagging. “Eating crow” is eating humble pie. The expression “bird brain,” for a stupid, foolish, or scatterbrained person, entered the English language in the early 1920s because people thought of birds as mere flying, pecking automatons, with brains so small they had no capacity for thought at all.

Yet, as Ackerman writes, scientists have come to realize the error of those ways:

Only lately has science illuminated how birds can be smart with a brain at best the size of a walnut. In 2016, a team of international scientists reported their discovery of one secret: birds pack more brain cells into a smaller space. When the team counted the number of neurons in the brains of twenty-eight different bird species ranging in size from the pint-size zebra finch to the six-foot-tall emu, they found that birds have higher neuron counts in their small brains than do mammals or even primates of similar brain size.

As Brian Villmoare writes in The Evolution of Everything: The Patterns and Causes of Big History:

One interesting fact is that, like primates, avians have very neuron-dense brains. In fact, the avian brain is as dense with neurons as primate brains (or denser), so that the brain of a macaw (a type of parrot) has as many neurons as the brain of a baboon. The corvids (crows and magpies) also have large numbers of neurons – ravens (at 1.3 billion neurons) have as many neurons as a squirrel monkey. The problem-solving abilities of birds is now appreciated far more than in the past. Birds are known to use tools in much the way monkeys do – picking up a stick or rock to dig or break into something. In tests of consciousness, corvids have been seen identifying themselves as individuals in much the way elephants and whales do. And birds are highly trainable, which means that they have a very flexible intelligence.

As Ackerman elaborates:

Neurons in bird brains are much smaller, more numerous, and more densely packed than those in mammalian and primate brains. This tight arrangement of neurons makes for efficient high-speed sensory and nervous systems. In other words, say the researchers, bird brains have the potential to provide much higher cognitive clout per pound than do mammalian brains.

Birds’ vocal organs are equally complex:

The voice box of birds is a structure called a syrinx, buried deep in a bird’s chest cavity. Sound emerges when the membranes of the syrinx vibrate, shifting the flow of air through the organ. The syrinx in birds varies from the bulbous resonance chambers and long looping trachea of ducks, geese, and swans—up to twenty times the expected length—which produce sound that exaggerates their body size, to the tiny pair of chambers in songbirds, controlled by delicate syringeal muscles. Some songbirds have such fine control over the multiple muscles in both sides of their syrinx that they can produce different sounds at the same time, in essence, singing a duet with themselves … [Birds] speak with their voices, their bodies, and their feathers. They may not have the facial musculature we primates use to express ourselves, but they can powerfully communicate their inner states with head and body, with facial feathers, crests, gestures, displays of wings and tail … The birds that carol the dawn chorus at my home halfway around the world in central Virginia—American robins, mockingbirds, warblers, sparrows, cardinals, finches—all descend from the early passerines of Australia, and like Pilliga’s birds, they all talk at once. The dawn chorus has always seemed to me a baffling behavior, everyone singing at the same time, louder and more energetically than at any other time of day, like a poetry slam where everyone simultaneously yells out their offerings. The chorus begins as early as four a.m. and lasts several hours until the sun rises and temperatures warm.

(I’ve used Cornell University’s Merlin app to identify, in just a five-minute span, over a dozen bird species singing away in my own backyard in Alexandria, Virginia.)

And it may surprise some that birds aren’t just singing – they’re communicating, sending detailed messages:

[Bird] mobbing calls—abrupt, short, loud, and repetitive— [are] alarm calls made in response to predators that are not moving at high speed and so are not an immediate or intense threat—usually a terrestrial predator like a snake or cat or, in this case, a perching bird. The call alerts other birds and signals them to fly toward the source of the call and join in with their own mobbing calls, or attack or mob the predator to drive it away. “There’s a predator here! Come help me harass it!” High-pitched flee, or aerial, alarm calls, on the other hand, usually mean there’s a predator in flight, which is a lot more dangerous for a bird. These calls are typically in a narrow bandwidth, with a lot of up-and-down amplitude, making the sounds harder to locate, especially for raptors with relatively poor hearing in that frequency range. Small birds use flee alarm calls to alert other birds to imminent danger from above, signaling them to freeze or take immediate cover, while not boosting their own chances of being snatched by a predator. Flee alarm calls send birds away from a threat; mobbing calls bring them toward it … Crows are among the most frequent mobbers, swooping and dashing down on a hawk from above and behind it, always keeping the menace in sight. Gulls often resort to the practice, too, with an unusual twist: vomiting on the predator with keen aim. Colonies of fieldfares fire from another orifice, ejecting feces on a predator in such volume and with such accuracy that the threatening creature is literally grounded or stopped in its tracks. If enough of these droppings-bombs hit their target, they can soak a bird’s wings so it can’t fly.

Naturalist David Attenborough narrates a nice demonstration of these fieldfare bird tactics in this clip from a BBC documentary:

Bird alarm calls act as much more than simple horns or sirens:

Given that birds need to respond to different threats in different ways, mobbing or fleeing, it makes sense that they would evolve different types of alarm calls. But communicating in this way—describing the specifics of a predator, whether it’s arriving by air or by ground—is called functionally referential signaling, and it was considered a big deal when it was first discovered in birds. For most of the past century, scientists thought the ability to refer to a specific object or event in the environment was unique to human communication. Animal signals reflected only an animal’s “internal state.” That changed in the late 1970s when scientists working with African vervet monkeys at the Rockefeller University found that the vervets produced distinctive calls for different predators—leopards, martial eagles, pythons, and baboons—and responded appropriately with different behaviors, climbing a tree for a leopard alarm call, for instance, or scanning the sky for an eagle alarm … [T]his ability to designate different kinds of danger was first demonstrated in domestic chickens, which produce a high-pitched screech in response to flying raptors and a kind of deep throaty garble when they see ground predators such as raccoons. “This categorization of threats into those that are flying and those that are on the ground seems to be a pretty common strategy among birds,” says [Jessica] McLachlan … The specificity goes even further … The chickadee-dee-dee mobbing alarm calls of black-capped chickadees contain messages—coded in the number of dees at the end of the call—about the size of a predator and hence, the degree of threat it represents. More dees means a smaller, more dangerous predator. A great horned owl, too big and clumsy to pose much of a risk to the tiny chickadee, elicits only a few dees, while a small, agile bird of prey such as a merlin or a northern pygmy owl may draw a long string of up to twelve dees … When I first learned this about the chickadee, it changed the way I heard all birds. What I’d taken as random chirps were in fact sophisticated signals to other birds, tweets of intelligence … A soft, high-pitched seet or sharp si-si-si signals a threat on the wing, a shrike or a sharp-shinned hawk. The signature chickadee-dee-dee flags a stationary predator, a raptor perched in the treetops or an eastern screech owl looming on a limb above. The number of those skipping-stone dees indicates the predator’s size and hence the degree of threat. More dees means a smaller, more dangerous predator. This may seem counterintuitive, but small, agile predators that can maneuver easily are a greater menace than larger, more cumbersome ones. So a pygmy owl may elicit four dees, while a great horned owl may garner only two. These are calls for reinforcements, used to recruit other birds to harass or mob the menace in a group defense calibrated to the magnitude of the threat.

So useful are bird calls for relaying information about the local environment that other animals learn from them, too:

So reliable are the chickadee’s vocalizations that other species heed their warnings … In fact, one study showed that more than seventy species of vertebrates eavesdrop on alarm calls: Birds eavesdrop on other birds, mammals on other mammals, mammals on birds, and birds on mammals. In North America, chipmunks and red squirrels grasp the meaning of bird aerial alarm calls. In turn, chickadees understand the alarm squeaks of red squirrels and will take cover in response. Three species of lizards even attend to bird alarm calls. Yellow-casqued hornbills of West Africa can distinguish between the eagle and leopard alarm calls of Diana monkeys.

Bird memories are also excellent:

It makes sense that birds are quick studies, good at gleaning lessons from a single experience, especially where danger is concerned. They can’t afford to forget. As behavioral ecologists have drily noted, “Few failures . . . are as unforgiving as the failure to avoid a predator: being killed greatly decreases future fitness.” … To study how birds learn about predators, biologist Blake Carlton Jones set up an experiment to see if a bird could learn about a novel threat after only one encounter. His “predator” was a black umbrella with big yellow eyes. At first, the birds showed no interest or alarm. But after the umbrella chased the birds just once for five seconds, they remembered the encounter, even four years later, and when the umbrella appeared, they instantly fled. No repeat lesson needed.

And birds are clever enough to be tricksters:

The bird world is rife with bluffs, masquerades, shams, and shell games. Some parent birds, such as piping plovers, feign a broken wing to draw predators away from the nest, fluttering erratically and making convulsive attempts to run, jump, or fly. Other birds distract predators by running in a crouched position like a small rodent. Still others, such as quail, feign death to fool their pursuers. Birds that cache their food, such as scrub jays, will move their food stashes several times if they know they’re being watched by another jay, shifting it to different locations or even fake-moving it but leaving it buried, a shell game aimed at confusing the viewer. These are all instances of physical deception.

Here's a video showing a killdeer bird faking his own wing injury to lure a potential predator away from the mother bird’s nest:

Bird tricks extend to impersonating other birds to achieve a variety of goals:

It’s not known how many bird species mimic. One database of avian mimics lists 339 species in 43 different families of songbirds. It’s rare in other bird groups … Among the accomplished vocal imitators in North America are the catbird, the northern mockingbird, and the brown thrasher, which is said to sing as many as two thousand different songs … European starlings imitate several other birds, along with everything from car alarms and cell phone rings to barking dogs. The blue jay’s ability to imitate a hawk is so good that I’ve often looked skyward vainly searching for a red-tailed hawk wheeling above, when the source of the hawk’s keening call is a blue jay in the nearby understory … Mounting research suggests they also appropriate calls and songs to deceive and manipulate others for their own profit … There are reports of blue jays mimicking not just red-tailed hawks, but raptors of all kinds, causing grackles and other birds to drop their food and flee, whereupon the jays seize the free meal. Even nestlings impersonate other young to glean more food … When disturbed while incubating, Carolina chickadees will imitate the sounds of a copperhead. The northern flicker makes a buzz like a hive of bees to deter predatory squirrels.

Birds, of course, use their brains to get food:

Herons all over the world have learned to bait their catches, carefully placing leaves and dead insects on the surface of the water to lure fish … Some birds get at food enclosed in hard shells or other tough packaging by dropping it on pavement to crack it open. Gulls drop clams, and crows and ravens drop nuts … Brown-headed nuthatches will … us[e] bits of bark from longleaf pines to pry under loose bark scales and devour the edibles beneath.

Here's naturalist David Attenborough again, showing the cleverness of crows in getting food:

Crows have demonstrated the ability to solve puzzles to get food in ways even five year-old human children can’t:

In 2018, the New Caledonian crow showed us that a bird can create tools by combining two or more elements—a feat so far seen only in humans and great apes. For the experiment, researchers caught eight crows in the wild of New Caledonia and brought them to a research station at Oxford University. They presented the crows with a puzzle box the birds had never seen before, which held a small food container behind a door with a narrow open slot along the bottom. They gave the crows long sticks, which the birds promptly inserted through the slot and used to push the food out through a window in the side of the box. Then the scientists gave the crows stick pieces too short to reach the food—some hollow and some solid, with different diameters so that they could fit inside one another. With no training or guidance, four of the crows put together the pieces within five minutes and used the longer compound pole to reach and extract the food. One bird was able to combine three or four elements to make one long tool—the first evidence of compound-tool construction with more than two elements in any nonhuman animal. This is truly a staggering accomplishment. Children can’t make these sorts of multipart tools until at least age five.

Here's a short BBC video showing a crow solving a similar problem:

And here’s a video of a crow seemingly just having fun, using a jar lid to repeatedly snowboard down the slope of a roof:

Birds have also done well figuring out ways to house themselves:

Healy, a professor of zoology at the University of St. Andrews in Scotland, has been arguing for more than a decade that nest building in birds is anything but simple, requiring sophisticated cognitive abilities—and, in this way, should be considered more like toolmaking. After all, nest building involves creating a new structure from a large number of objects—sticks, mud, mosses, grasses, feathers, snakeskins, spider silk. It requires making informed decisions about location and choosing appropriate materials to shield young from the elements and protect against predators. And, often, it requires coordination and collaboration between male and female birds. Penduline tits, for instance, build together as a pair for two weeks—one working on the outer structure of the nest, the other on the lining.

Beyond their brains, bird senses are so much more varied than ours that, while we can understand how birds sense, it would be impossible for us to imagine exactly what that would look like:

The human sensory bias has sometimes blinded us to the differences in bird sensory capacities—and their diversity. But new ways of studying bird perception has helped us take a bird’s-eye view of the world, changing the way we see what they see and revealing the hidden layers of their reality—how they see unimaginable explosions of color and pattern, hear sounds inaudible to our ears, smell the shape of whole landscapes … Birds top us in color vision, too. They see hues beyond our imagining. Humans have three types of color-receptive cones in our retinas, blue, green, and red. Birds have a fourth color cone that is sensitive to ultraviolet wavelengths. We are thus “trichromatic,” and most diurnal birds are “tetrachromatic.” With their extra UV cone, birds can distinguish shades of color we can’t tell apart, allowing them to spot prey well camouflaged against the uniform background of a grassy field or leafy forest floor, and to detect things invisible to us—like the trail of urine left by a vole.  But it goes beyond this. Birds see a massive spectrum of color our brains are simply incapable of processing. “It’s not just that they can see wavelengths of colors in a part of the spectrum we can’t see,” says Mary Caswell Stoddard, an assistant professor of ecology and evolutionary biology at Princeton University, who studies avian color vision. “It’s that ultraviolet light is a fundamental part of many of the colors they perceive. They’re experiencing another whole dimension of color—all the colors we can see, with varied amounts of UV mixed in. So it’s not simply human vision plus some purplish UV colors. It’s a complete reimagining of the color experience.”

And try imagining what it would like to see through a duck’s eyes, atop a lake.  Each eye, placed flatter on the sides of its head than ours, would see a panoramic view including the surface of the water and the sky (great for spotting predators in all directions).

And some birds have developed amazing capacities to hear sounds.  Think of this the next time you see a robin hunt for a worm:

When vision is limited, American robins search for earthworms by sound. Watch them in a field or on a lawn: They run a few steps, then lunge and drive their bills deep into the soil, more often than not snagging an earthworm. Scientists have recorded capture rates as high as twenty earthworms per hour. Mask all sound with white noise, as the researchers did, and the robins are not nearly as successful.

All this is the result of evolutionary processes that trace birds back to their dinosaur ancestors:

Birds are dinosaurs, descended from the lucky, flexible few that survived whatever cataclysm did in their cousins. We are mammals, related to the timid, diminutive shrewlike creatures that emerged from the dinosaurs’ shadows only after most of those beasts died off. While our mammal relatives were busy growing, birds, by the same process of natural selection, were busy shrinking. While we were learning to stand up and walk on two feet, they were perfecting lightness and flight. While our neurons were sorting themselves into cortical layers to generate complex behavior, birds were devising another neural architecture altogether, different from a mammal’s but—in some ways, at least—equally sophisticated … Consider a bird’s brain relative to its body weight, and it comes out more like a mammal … And the brain of a chickadee? It has double the brain size of birds in the same body-weight range, such as a flycatcher or a swallow … To meet the constraints of flight, nature has in fact considerably lightened a bird’s load with a skeleton that blends strength and airiness. Some bones have been fused or eliminated. A light beak made largely of keratin has replaced a heavier, toothy jaw. Other bones, such as wing bones, are pneumatic, almost hollow but reinforced with strutlike trabeculae to keep them from buckling. A bird’s bones are dense only where needed—even denser than the bones of their mammal counterparts—in the legs and in the deep solid breastbone that anchors the wings. (So powerful is the downstroke of a bird’s wing that it produces force enough to lift twice the animal’s body weight into the air.) When biologists examined the genes involved in a bird’s skeletal system, they found that birds possess more than twice as many genes for bone remodeling and resorption than mammals do. Most bird bones are hollow and thin walled, yet surprisingly stiff and strong. The paradoxical result sometimes boggles the mind: A frigate bird with a seven-foot wingspan has a skeleton that weighs less than its feathers … Evolution has found other ways to streamline or totally eliminate a bird’s unnecessary body parts. Bladders have been done away with. The liver has dwindled to a mere half gram. A bird’s wild knot of a heart is four-chambered and double-barreled like our own, but tiny, with a beat far more rapid (between 500 and 1,000 times a minute for black-capped chickadees; 78 for humans). Its respiratory system is quite extraordinary, proportionately larger than in mammals (one fifth of its body volume, compared with one twentieth in mammals), but much more efficient. Its “flow-through” lung, encased in a rigid trunk, maintains a constant volume (in contrast with mammalian lungs, which expand and contract in a flexible body) and is connected to an intricate web of balloonlike sacs that store air outside the lungs … Only in the breeding season is a bird burdened with heavy sex organs; for most of the year, testes, ovaries, and oviducts are vanishingly small … Birds evolved from dinosaurs during the Jurassic period, 150 million to 160 million years ago. In fact, says paleontologist Stephen Brusatte of the University of Edinburgh, “we find that there is no clear distinction between ‘dinosaur’ and ‘bird’. A dinosaur didn’t just change into a bird one day; instead, the bird body plan began early and was assembled gradually, piece by piece, over 100 million years of steady evolution.” … [I]t baffles the imagination to think that the tiny flashlike chickadee could have arisen from the big beasts of vanished ages.

As Ackerman writes, if you watch birds closely, you’ll quickly realize how fast they move.  It’s as if time moves faster for them:

Webcams and miniature video cameras are offering a close look at behaviors normally hidden or occurring at such speed they’re too quick for our eyes. The world of birds moves about ten times faster than ours, and only with high-speed video can we see some of their amazing feats: tap dancing to a beat, turning somersaults in the air, executing display moves as complex, coordinated, and beautiful as those of any gymnast.

Birds must see us as slow, lumbering beasts.

And as crows can solve puzzles faster than human five year-olds, their brains seem to move faster, too.  As Ackerman writes:

What kind of intelligence allows a bird to … find its way to a place it has never been before, though it may be thousands of miles away? … (I would flunk these sorts of intelligence tests as readily as birds might fail mine.)

But it seems that birds’ ability to navigate long distances with precision relies not only on the brains, but on the biology of quantum physics:

One model holds that birds “see” magnetic fields with special molecules in the retina activated by certain wavelengths of light. Magnetic signals seem to affect the chemical reactions of these molecules, either speeding them up or slowing them down, depending on the direction of the magnetic field. In response, the retinal nerves fire signals to the visual areas of a bird’s brain, making it aware of the field’s direction. It all occurs at the subatomic level, involving the spin of electrons, which suggests something extraordinary: Birds may be capable of sensing small quantum changes. The sensing seems to involve a part of the forebrain linked to the eyes, known as cluster N. If cluster N is damaged, birds can no longer sense which way is north. What would they actually see? It’s hard to know. Perhaps a ghostly pattern of spots, or of light and shade, that would remain in place as the bird moves its head from side to side.

That will be subject of the next essay, in which we’ll explore Jim Al-Khalili and Johnjoe McFadden’s Life on the Edge: The Coming of Age of Quantum Biology.