The Science of Birds - Bird Brains

Episode Date: June 18, 2024

This episode—which is Number 98—delves into the fascinating world of the avian brain. Despite the long-standing misconception that "bird brain" equates to being unintelligent, recent scientific research reveals that birds possess remarkably sophisticated brains, rivaling the intelligence of primates and even humans in some respects. By tracing the evolutionary paths of both mammals and birds from a common ancestor, I explain how birds have developed unique brain structures that enable complex thought processes, decision-making, and problem-solving.We'll explore the anatomical intricacies of a bird's brain, breaking down its basic architecture into the forebrain, midbrain, and hindbrain. I highlight the critical role of structures like the hyperpallium and the dorsal ventricular ridge in enabling advanced cognitive abilities. Additionally, the discussion touches on brain plasticity, neuron density, and the specific regions involved in vocalization and memory.~~ Leave me a review using Podchaser ~~Link to this episode on the Science of Birds website Support the show

Once upon a time, about 320 million years ago, there lived a small creature. It scurried around on four legs, had skin like a reptile, and it laid eggs. This creature made its home in a humid forest at the edge of a swamp. Such habitats were common across the vast continent of Pangaea in those days. Two independent and wildly different animal lineages that exist today, both trace their ancestors. all the way back to this one species that lived 320 million years ago. One of those lineages is the mammals. Inside its skull, that ancient ancestral creature had a relatively small, reptile-like brain.

But the brain's capacity for deep thoughts, for hopes and dreams, for the ability to do rocket science, in other words, its capacity for intelligence, increased generation after generation after generation in the lineage of descendants that became the mammals. Over hundreds of millions of years, mammal brains became more complex and proportionally larger when compared to their body sizes. You and I represent the latest model when it comes to smart mammals with oversized brains. But remember that mammals are just one of two lineages that descended from that ancient reptile-like creature. Birds, represent the other lineage. Over the last 320 million years, this second lineage went on its own

wild evolutionary ride, leading eventually to feathered dinosaurs that could fly and sing beautiful songs. This was a very different path than the one taken by mammals. Animals in the bird lineage ended up, of course, with bird brains. And as we all know, having a bird brain means you aren't very smart. You're running mostly on instinct. For example, I read in the news recently that one politician insulted another politician by calling them a birdbrain. First of all, rude, but second, you probably know that calling someone a birdbrain isn't really an insult, even if it was meant to be. If you listened to episode 25 of this podcast, you know that birds are actually quite intelligent. Some are just as smart as primates like monkeys, and, yes,

even humans, arguably. So, even though the evolutionary lineages of mammals and birds have been following separate paths for over 300 million years, they independently ended up possessing far more intelligence than other vertebrates like fish, amphibians, and reptiles. The physical structures of mammal brains and bird brains have plenty of similarities because of their shared, albeit ancient, ancestry. But brain anatomies in these animals are also different in many ways. They represent two different tools for solving the same problem, like an iPhone versus an Android phone, or maybe like Xbox versus PlayStation, or solar panels versus wind turbines. You get the idea. Scientists in recent decades have unraveled some mysteries of the avian brain. They've shown us how

the unique structure and organization of this organ give rise to consciousness and intelligence in birds and allow birds to do the amazing things they do. Hello and welcome. This is the science of birds. I am your host, Ivan Philipson. The Science of Birds podcast is a light-hearted exploration of bird biology for lifelong learners. This episode, which is number 98, is all about the avian brain. Episode 25 of the podcast was all about bird intelligence. Today, our focus is on anatomy, more on the physical structure.

of a bird's brain. One of the big reasons we all used to think that birds are dumb-dums is a misinterpretation of bird brain anatomy. Scientists studying bird brains back in the day compared them to human brains,

naturally. The human brain was this sort of gold standard for what a vertebrate brain capable of high intelligence is supposed to look like. The scientists eventually concluded that bird brains are, quote-unquote, primitive. They're missing some of the more complex structures found in human brains. Therefore,

birds must not have the capacity for high intelligence. For example, at first inspection, it appeared that birds lack a cerebral cortex. Without such a structure, birds were assumed to run mostly on autopilot, on pure instinct. But further research revealed that birds actually do have brain structures that work like the cerebral cortex to generate complex thought processes, like decision-making, planning, and problem-solving. The structures in bird brains may look different, but they're derived from some of the same tissues as those of the more advanced parts of the human brain. This new interpretation and understanding of the avian brain has helped to revolutionize our appreciation for bird intelligence. I'll go into more detail,

about all of this soon. But first, I want to point out that brain anatomy, including the relationships between brain structure and function, is a complex topic. It involves a ton of scientific terminology, jargon, and acronyms. Honestly, I find it all overwhelming and confusing sometimes. Nobody wants to be overwhelmed or confused, right? So today I'll try to keep the discussion fairly basic and as understandable as I can. I'll try to minimize the amount of scientific jargon. That said, I know that as a listener of this podcast, you're eager to learn. You aren't scared off by a few new words and concepts.

And that's great. In any case, some jargon will be unavoidable. Sorry, not sorry. And with that, it's time to take a journey inside the skull of a bird, to explore the nooks and crannies of the amazing avian brain, a highly efficient, compact, and complex marvel of nature. We'll begin by looking at the lay of the land, so to speak, at the basic architecture of a bird's brain,

as well as some of its key features, To help you visualize the things I'll be talking about today, I made a simple diagram illustration thing and put it in the show notes. That'll be on the Science of Birds website, Science of Birds.com. I should mention that brain shape and orientation vary quite a bit among the different types of birds. That isn't surprising, perhaps, when we think about the wide diversity we see among the brains of mammals.

Imagine what a kangaroo brain might like. look like compared to the brain of a mole or a dolphin. But we'll mostly be talking about the structure of a typical bird brain today. In terms of this organ's overall shape, it's vaguely similar to that of a human brain. And like the human brain, the avian brain is divided into different sections responsible for various functions. The three basic sections are the forebrain, the midbrain, and hind brain. The forebrain, or cerebrum, is the largest section. It has a bulbous shape. It's most plump in the middle and narrows a bit at the front end, the anterior end. The forebrain is divided into two halves, a left hemisphere and a right hemisphere. Now, when you picture a human

brain, one of the outstanding features that probably comes to mind is the cerebrum's wrinkled, folded surface. If a human forebrain looks sort of like a head of cauliflower, a bird's forebrain looks more like a swollen water balloon, like the water balloons my friends and I used to huck at cars that passed by my house. In other words, bird brains don't have all those wrinkles. They're relatively smooth on the surface. We'll look more closely at the forebrain section in a few minutes. For now, let's move on to the midbrain. The avian midbrain consists of several structures that play crucial roles in sensory processing, motor control, and coordination. The most conspicuous part of the midbrain in a bird is the optic tectum, T-E-C-T-U-M. This is a feature of birds, humans, and all

other vertebrates. The optic tecta, tectum is the singular form of the word tecta, is plural. The optic tecta are bulbous sort of egg-shaped structures that sit below and slightly behind the cerebrum. Their orientation and relative size vary from one type of bird to another. The optic tectum processes visual information. It receives input from the eyes and helps birds with visual tasks such as tracking moving objects, coordinating eye movements, and controlling behaviors that rely on vision. The hind brain sits behind the rest of the brain, or in some types of birds, it may sit below all the other brain structures. Overall, the hind brain coordinates involuntary, but vitally important, functions. Things like breathing, heart rate, muscle coordination, and

balance, as well as other basic processes in the body. The cerebellum, with its wrinkled surface made of parallel grooves, is the most obvious part of the hindbrain. It coordinates movements of the limbs and other body parts and maintains balance. The cerebellum receives input from the senses as well as information from the forebrain and midbrain. It uses all of this information to fine-tune commands to nerves in the wings, legs, and elsewhere in the body to ensure smooth and coordinated movements. Birds need a supercharged cerebellum to maintain control of their muscles during flight. So that was a little information about the forebrain, midbrain, and hindbrain. Birds are small animals, at least when compared to humans and other mammals of similar size.

Bird brains are, not surprisingly, small in the absolute sense. A typical human brain weighs about three pounds, which is about 1.36 kilograms. However, some human brains, like mine, may be significantly smaller. But even my undersized brain is positively gigantic when compared to the largest known bird brain, which belongs to the emperor penguin. That species brain weighs about a tenth of a pound, or 46 grams. Yeah, take that, penguin. My brain may be small by human standards,

but I am a godlike genius compared to you with your little 46 gram brain. At the other extreme, the smallest bird brain for which we have measurements is the one belonging to the Cuban emerald, which is a species of hummingbird. its brain weighs only 0.000-2-8 pounds, which is 0.13 grams. That's about as heavy as a small paperclip. And side note,

the Cuban emerald Ricordia Ricordia is called Sun Tsun by people in Cuba. Sun Tsun is spelled Z-U-N-Z-U-N. I don't know. I just think that's a pretty cute name for a hummingbird, Sun Tsun, especially for one with such a teeny tiny brain.

Anyway, the brain of your standard issue rock pigeon weighs about 0.07 ounces, or 2 grams. And it's roughly the size of a grape. But all of those are absolute numbers. When we consider the size of bird brains relative to the body sizes of the creatures that own them, well, that's a different story. Birds, like humans and other primates,

have relatively large brains for their body weight. A bird's brain is between 2 and 9% of its total body mass, depending on the species you're looking at. This is similar to the ratio seen in most mammals. However, a bird has a much larger brain than, say, a lizard of equal body weight. One word I've seen used to describe the brain sizes of birds is hyperinflated. Yeah, inflated, like the... water balloons my friends and I used to throw at passing cars. We were like 11. We would hide on the

roof of my house, staying hidden from the angry drivers. I once lobbed a balloon high into the air such that it traced an elegant arc through the summer sky, an arc that terminated in a deeply satisfying, watery explosion on the head of a guy driving his convertible car down my street. I know, I know, this was bad behavior. But hey, we were kids. We were kids. It was summer. We had a bag of water balloons and an assortment of colors. What were we supposed to do? Anyway, not only do birds in general have these hyperinflated, relatively large brains, the smartest bird species have even larger brains proportional to their body size. For example, chickadees, famous for their ability to remember the locations of thousands of stashed seeds,

have brains twice as large as many other songbirds of similar body weight. New Caledonian crows, which I talked about in episode 25 of the podcast, are often considered the smartest birds in the world. The brain of this species weighs about 0.16 pounds or 7.5 grams. The entire bird weighs between half a pound and one pound. That ratio of brain size to body weight is similar to what we find in some small monkeys. This whole brain-sized-to-body weight comparison has often been used as a proxy for animal intelligence. The larger your brain is compared to your body, the smarter you are, theoretically. Some scientists have questioned this approach, however. An alternative that might be more useful is to look at the number of neurons in

the forebrain. The more neurons packed into the cerebrum, the smarter you're likely to be. Just as a reminder, a neuron is a special type of cell in the brain and nervous system that helps send and receive information. These cells are the fundamental building blocks of the brain. Neurons connect with each other to form a communication network in the brain and throughout most of the body. When we feel like being mean, and we say that so-and-so has only 10 brain cells, we mean that they have only 10 neurons in their brain. Anyway, it turns out that birds do indeed have a high density of neurons in their forebrains. So even using this more modern proxy of intelligence, birds also win.

We'll talk more about neurons in a bit, but before that, let's investigate the forebrain to understand this structure more deeply. In humans, the forebrain has a special outer layer called the pallium, P-A-L-L-I-U-M. If the brain is like an orange, the pallium would be sort of like the orange peel. The most famous part of the pallium in the human brain is the cerebral cortex. This is the outermost layer of the brain. It's responsible for our higher-level thinking skills, such as reasoning, imagination, planning, problem-solving,

and, in my case, making podcast episodes about birds. Remember from earlier that the historical way scientists viewed the avian brain was that it's relatively primitive and lacks a cerebral cortex. This led people to make conclusions like, birds can't use reason to solve problems, and birds have no imagination, and birds suck at making podcasts. No, birds may not have a cerebral cortex in the same form as it exists in mammal brains, but birds do have a pallium. Scientists have shown that the same cluster of cells in the brains of both mammal and bird embryos grows into the cerebral cortex and avian pallium,

respectively. So these structures appear to have a common origin. They're made of the same raw material. The avian pallium expanded in size and evolved into a unique structure over the last 300 plus million years. Today, this part of a bird's brain does pretty much all the same stuff as the cerebral cortex in mammal brains. Among other things, the pallium seems to be the physical basis for a bird's consciousness. The pallium in birds makes up most of the forebrain. But unlike the pallium in mammal brains, it isn't just the outer layer, the orange peel. Instead, the pallium of birds is a thick, multi-layered structure. Perhaps the most prominent layer is the hyper-palium. This forms a sort of bulge on the top and front of the forebrain. This part of the brain is

unique to birds, and is thought to play a role in spatial navigation and song learning. Overall, the hyperpalium is a multifunctional region that's essential for many of the more sophisticated behaviors in birds. It works more or less like the cerebral cortex in mammals. It processes sensory information, orchestrates voluntary movements of the body, plays an important role in communication, learning, memory, and so on. The hyperpaliq is most well developed in super smart birds, like parrots and members of the family Corvody, crows, ravens, and magpies. Lying just below the hyperpalium is the dorsal ventricular ridge, or DVR, for short.

This region makes up the bulk of the pallium. The DVR has many functions and is especially important for processing information from the eyes and ears. However, despite the familiar acronym, DVR, the dorsal ventricular ridge in birds does not allow them to record their favorite cable TV shows and then skip the commercials while watching them later. And while we're at it, how about I throw another acronym at you? NCL. This one stands for Nidopalium Cotolaterally. The NCL is one of several layers or subsections of the DVR. You can think of it as the

equivalent of the prefrontal cortex in your brain. In case you're not sure what the prefrontal cortex is, it's like the ultimate command center for your brain. It's responsible for higher level thinking, decision making, planning, and controlling your behavior. It helps you solve problems, set goals, and at least occasionally think about consequences before you act. Like maybe if you grab that bag of Doritos chips and sprint out of the grocery store without paying for it, you might get tackled in the parking lot by the security guard, and you might end up in a maximum security prison for the rest of your life. Consequences, yo. Basically, the prefrontal cortex is the part of the human brain that helps us make smart choices and stay focused on what's

important. It can help us override our more primitive impulses, like the urge to steal bag of Doritos. So the Nidopalium codolaterally in bird brains, the NCL, seems to work in a similar way. Okay, so how about a mini review of the avian forebrain so far? The bulk of the forebrain, otherwise known as the cerebrum, is formed mostly of a multi-layered structure called the pallium. The topmost and forward-facing layer of the pallium is the hyperpalium. Below that is the DVR, which includes several other distinct layers. The hyperpalium and DVR and the layers within the DVR are all sub-regions of the pallium. And one important part of the DVR is a layer called the Nidopalium Cotolaterally or NCL.

And that is like the overall command center of a bird's brain. Got it? Cool. That was our mini-review. Moving on. The last part of the forebrain I want to mention is the olfactory bulb. This structure is located at the front of the forebrain, and it's responsible for processing olfactory information.

In other words, smells. Although the sense of smell is generally less developed in birds compared to mammals, it still plays an important role in various behaviors for some species, such as foraging, navigation, and social interactions. The size and functionality of the olfactory bulb can vary significantly among different types of birds, depending on their reliance on the sense of smell. Kiwis and turkey vultures, for example, rely heavily on their senses of smell. And just as you might expect, each of these birds has a relatively ginormous oversized olfactory bulb,

jutting out at the front end of its brain. Zooming out now to look at the entire avian forebrain, we see that it's different from a mammal's brain in another important way. The gray and white matter of bird and mammal brains are organized differently. In very basic terms, gray matter in a brain is made of neuron cell bodies, as well as some other types of brain cells and capillaries. gray matter contains most of the brain's synapses between neurons. Its function is to process and integrate information.

Gray matter is also responsible for muscle control and high-level processes like decision-making. White matter, on the other hand, is made primarily of axons, which are the long, tail-like extensions of neurons that carry electrical signals between neurons. In white matter, the axon of each neuron is surrounded by a sort of sheath made of fat. This is what gives white matter its pale color. The role of white matter is mostly to transmit signals rapidly, both within the brain and to and from the spinal cord. In the mammalian cerebral cortex, gray matter forms the outermost layer. Meanwhile, the deeper parts of the brain are mostly white matter.

So there's this layered structure. But gray and white matter are not layered like this in the avian brain. Instead, gray matter in the avian pallium is organized into clusters and regions. Tracts of white matter, sort of like dense bundles of USB cables, connect the various regions of gray matter. So in birds, the separation of gray and white matter is much less obvious. And yet, this is apparent. an equally effective organization structure for processing complex information.

Now, remember that the forebrain has two hemispheres, a left side and a right side that look like mirror images of each other, just like in our brains. And like humans, birds show something called lateralization in their brain functions. This is where certain tasks are preferentially processed in only one hemisphere of the brain. So there's a sort of division of labor between, the two sides. In humans, for example, the left hemisphere is more involved in language, talking, reading, writing, etc. A couple of strengths of the right hemisphere are processing

emotions and creative tasks like making music and art. Also, remember that the right hemisphere controls the left side of the body and vice versa. That's really weird, I know, but it's just how the vertebrate brain is wired. So what about birds? In songbirds, as an example, the left hemisphere is often dominant for learning and singing songs. Pigeons and chickens give us another example of brain lateralization. They have lateralized visual processing. They tend to use their right eye, and thus the left hemisphere of the brain, for tasks involving detailed visual discrimination, like finding tiny morsels of food on the ground. Meanwhile, the right hemisphere in these birds, which is connected to the left eye, is more involved in scanning the environment

for predators or anything out of the ordinary, like UFOs or malevolent spirits. All this brain lateralization stuff might have you thinking about handedness. If you're among the 90% of humans that are right-handed, that means the left side of your brain is dominant. So if birds show lateralization in their little brains, does that mean they can be left or right-handed? The answer is yes. Even though birds don't have hands, they can be right-eas or lefties. For example, individual red-necked fallaropes are consistent in whether they spin left or right while they forage in the water. And just to explain that a little bit, all three fallow ropes are consistent. rope species, shorebirds in the Sandpiper family, spin on the surface of water when they forage.

They're like little spinning tops or ballerinas. They kick their feet underwater to create a small upwelling vortex that brings tiny prey close to the surface. Researchers have observed that, at least in the red-necked fallow rope, individuals are either lefties or righties when it comes to their spin direction. Handedness, or I guess footedness, is also common in birds as diverse as parrots, pigeons, flamingos, owls, and songbirds. Most New Caledonian crows, those super-smart corvids, are famous for their ability to make simple tools to access food. The species, too, demonstrates quote-unquote handedness because most individuals favor their right eye while crafting a tool using their beak and feet.

In this section, I'd like to talk a little about memory. There are several major kinds of memory, such as associative learning, visual memory, auditory memory, and remembering sequences of events, just to name a few. Another category is spatial memory, and that's what we'll focus on. The part of a bird's brain that plays the biggest role in spatial memory is the hippocampus. This is yet another part of the forebrain. It's a small region located near the highest point of the forebrain, near the midline. The hippocampus is closely linked to other parts of the forebrain,

such as the hyperpalium and parts of the DVR. These regions help birds process visual and spatial information. They work together to form a kind of network. where memories of places and objects are stored and recalled. Like mammals, birds have a well-developed hippocampus. It's essential for both spatial memory and navigation. Memories processed in the hippocampus help birds with things like remembering where to go on migration, returning to their favorite feeding areas, finding their nests, and escaping the labyrinthine interior of an IKEA store. A supercharged hippocampus is especially important for bird species that cache food,

such as chickadees and Clark's nutcrackers. Remember that caching, C-A-C-H-I-N-G, is the behavior where a bird stores little bits of surplus food here and there. For example, a chickadee wedging a seed under some tree bark. The bird comes back to retrieve its cached stash, days, weeks, or even months, later. Some birds can remember the locations of hundreds or thousands of caches. I talked about some of this in the podcast episode I did on Avian Intelligence. Again, that's episode 25. Several bird families specialize in the behavior of caching, corvety, citadie, and peridi. In other words, the crow, nut hatch, and chickadee families. It turns out that birds in these groups have

significantly larger hippocampuses, or hippocampi, than birds that don't show caching behavior. Researchers have discovered something amazing about the hippocampi of chickadees. The hippocampus of a chickadee grows much larger in the autumn, almost 30% larger. These little birds stashed seeds all over the place in late summer and autumn as they prepare for the lean winter months ahead. Having an enlarged hippocampus allows a chickadee to power up its spatial memory. When spring rolls around, the chickadee's hippocampus shrinks back down. That's because live insects and other invertebrate prey become abundant in spring,

so the bird doesn't need to rely as much on cashing during the warm months. One of the amazing things about this dynamic hippocampus power-up thing is that the birds are able to form new neurons every autumn. This brings us to the topics of brain plasticity and neurogenesis. Plasticity has the word plastic tucked in there, right? An object with plasticity is something easily shaped or molded. Plasticity of the brain, also called neuroplasticity, describes its ability to grow, shrink, or change. The growing and shrinking of a chickadee's hippocampus is one example.

Neuroplasticity is a superpower that allows a bird's brain to change and adapt to new experiences and to seasonal or environmental changes. It helps birds learn and even recover from brain injuries. The brain regions that control singing can also show plasticity. For example, in song sparrows, a familiar backyard bird in North America, one part of the brain strongly involved with singing nearly doubles in size from winter to spring. The birds grow a bunch of new neurons. Apparently, song sparrows need more neurons in that part of the brain during the breeding season. Maybe the complexity of their songs demands twice the computing.

power. Until fairly recently, scientists thought that only baby birds and the babies of other vertebrate animals could make new brain cells like this. The formation of new neurons is called neurogenesis. We used to think that once a bird or mammal reached adulthood, that was it. No new neurons for you, Buster. If you ended up with only 10 brain cells, well, they're then, that's all you've got to work with. This idea that neurogenesis is impossible in adults was firmly held and persisted until about the 1980s. Then there were some breakthrough scientific studies

that revolutionized our understanding of neurogenesis, and those studies were on birds, specifically the island canary, serinus canaria, also known as the wild canary, or, as I prefer to call it, O.G. Canary. Yes, this is the wild ancestor of the world famous domestic canary. Anyway, researchers discovered that neurogenesis in adult canaries is a thing and that it

happens in the part of the brain associated with song during the breeding season. We're talking the same part of the brain that swells to twice its normal size every spring in song sparrows. In the decades since, scientists have discovered all sorts of examples of neurogenesis in the brains of adult vertebrates, and that includes good old homo sapiens. Thanks to birds, we know that new neurons can form in adult humans. My understanding is that neurogenesis in the human brain occurs mostly in the hippocampus, sort of like chickadees. So our brains, too, show some plasticity when it comes to spatial memory and all of that. I wish I could grow just a few more neurons in my hippocampus,

so I would stop forgetting my phone charger every time I'd check out of a hotel room. Let's look more closely now at the parts of the avian brain associated with vocalizations, with songs. As you might guess, the brains of songbirds are the most sophisticated in this regard. There are quite a few regions in a bird's brain involved in the production of songs. They aren't all located in just one place. Some are in the forebrain, some are in the hind brain. But information flows back and forth between all of them through bundles of neurons,

connecting them into a well-coordinated network that scientists call the vocal control system or song control system. The higher vocal center, or HVC, is the central hub of this network. It's located towards the back and top part of the brain, within the upper regions of the forebrain. The HVC receives and integrates auditory information from the ears and coordinates with other regions in the vocal control system. For example, signals from the HVC are sent to a region called the robust nucleus of the archopalium. That's way too much of a mouthful, so scientists have thankfully given this brain region the compact acronym RA. So the RA receives inputs from the HVC, and then it sends signals all the way down to the brain stem, where there are

clusters of brain cells that control the muscles that allow a bird to make crazy, amazing sounds like this. Now if all of this terminology about the vocal control system is confusing and seems really complex, that's because it is. And we're only just barely scratching the surface here. We're only scratching the smooth water balloon-like surface of a bird's squishy little brain. But I promise we're almost done with the technical jargon. Now I want to tell you about Area X. Wait, wait, with a name like that, I got to say it like, Area X. I mean, doesn't Area X sound like the name of a top secret storage warehouse where the government hides things like magical artifacts from Atlantis and technology recovered from crashed alien spaceships? Well, Area X is a

is actually another component of the vocal control system in birds. However, it's found only in the true songbirds, those species belonging to the suborder passeri within the order passeriformis. Area X is involved in song learning and in the refinement of song patterns, particularly during the juvenile life stage. It sparkles with activity most strongly

when a bird is learning a new song. Location-wise, it sits deep in the center of the brain, not too far from the HVC and the RA. Area X receives inputs from the HVC and connects to other parts of the vocal control system. Scientists discovered that in songbirds, there are enormous differences between males and females in the vocal control system. In zebra finches, for example, the network of song-related brain regions is up to 10, times larger in males than in females. This is certainly interesting because female zebra finches never sing. Sex differences have also been discovered in many other songbird species, but few are as dramatic as what we see in zebra finches. The size differences in the vocal control system

between males and females could be the result of chemical differences, the effects of sex hormones like testosterone. But an alternative hypothesis is that maybe these brain differences between the sexes are the result of genes rather than hormones. So which is it? Hormones or genes? How scientists found the answer was pretty wild. A study published in 2003 explained how a genandromorph zebrafinch was discovered in a lab

of population. A genandromorph is an extremely rare, thing in nature. It's an animal with a genetic split down the middle where one half of the animal, in this case a zebra finch, is male and the other half is female. So in this particular finch in the 2003 study, the researchers could see how the brain was different on each side. Even though the blood and hormones were the same on both sides, the HVC, the higher vocal center, was bigger on the male side and smaller on the female side. This means that even though hormones can affect how the brain develops, the differences we see in zebra finches and probably other songbirds as well

are mainly due to genes. As we talked about earlier, bird brains are mostly small in the absolute sense. A pigeon's brain is the size of a grape and yada, yada. And yet, bird brains are powerful little thinking machines. So how exactly do these compact brains manage their impressive cognitive feats? The unique organizational structure of the avian brain, the stuff we've been talking about, might have something to do with it. But at least to me, it seems like that structure is simply an alternative way of building a brain that's as smart ounce-for-ounce as a similarly sized mammal brain.

But it turns out that if we're making such an ounce-for-ounce comparison of intelligence, the avian brain punches above its weight, so to speak. The secret lies in the high density of neurons in the avian brain, especially in species like songbirds and parrots. These birds have a remarkable number of neurons packed into their forebrains. For example, a common one, Raven's brain, although only one-sixth the size of a rhesus macaque's brain, actually has about one-third the number of neurons. Even more impressive, the proportion of neurons in the

pallium of birds is higher than in many primates. This dense packing allows for shorter distances between neurons, potentially leading to faster processing speeds and advanced cognitive abilities. But neurons are little energy hogs. They're energy-intensive, typically consuming about 70 to 80% of the brain's energy, which comes from the sugar glucose. Given this fact, you might think that maintaining such a high number of neurons would be energetically costly, too costly. However, birds have evolved to meet this challenge efficiently. Research on pigeons has shown that avian neurons require significantly less glucose than mammalian neurons, more than three times less, in fact. How is this possible? Well, first off,

the neurons in a bird's brain are smaller than those of mammals. In very simple terms, smaller neurons have a lot less going on at the molecular level, so they need less energy to do their thing. Second, birds have higher body temperatures, which can reach up to 108 degrees Fahrenheit or 42 degrees Celsius in pigeons. The higher temperatures speed up the activity of certain proteins inside the neurons reducing their need for energy. This efficient high-density neuron arrangement means that smart birds like parrots and corvids can achieve greater cognitive power per ounce or per gram of brain tissue than many mammals. The compact high-performance brains of birds are a beautiful example of evolutionary adaptation.

Birds need sharp brains to handle the complexities of flight, foraging, and to handle the drama of their social lives. But they can't afford the weight of a large brain. So evolution has crafted avian brains to be both lightweight, energy efficient, and incredibly powerful, allowing birds to thrive in just about every habitat on Earth. The avian brain is a marvel of nature's engineering. For over 300 million years, it's been honed through natural selection to be lean, mean, and highly efficient, perfectly suited for the demands of flight and survival. So it's kind of crazy to think that scientists once thought birds are dummies.

Scientists back in the day had studied the structure. of the avian brain, misinterpreted that structure and decided that it prevents any higher-level thinking in birds. Thankfully, other researchers didn't just accept this as fact. They kept questioning and deepening our understanding of the avian brain. They helped all of us basically do a 180. We thought birds were so incredibly dim-witted that we used bird brain as an insult. But now we appreciate birds for being among the smartest creatures on earth. And, one could argue, they're also among the most successful animals on the planet. They're wildly diverse, and as I was just saying, they live just about everywhere. Birds today are all the descendants of one small lineage of dinosaurs,

a lineage that was lucky enough to survive the mass extinction 66 million years ago that wiped out all the other dinosaurs, as well as countless other forms of life. We can't know for sure why birds survived that great extinction, but there's some recent scientific evidence that their brains might have had something to do with it. A study published in 2021 in the journal Science Advances examined a new fossil specimen of Ictheornis Disbar, a bird from the late Cretaceous period. So this critter was alive not too long before the asteroid smashed into Earth. This new fossil has a nearly complete skull of Ictheornis. It was analyzed using X-ray computed tomography, in other words a CT scan, to reconstruct the bird's skull and brain. This provided new insights into its brain structure.

While Ictheornis had some advanced features, its brain was more like that of earlier birds and non-avian dinosaurs. It didn't have the expanded brain regions found in modern birds, the ones we've been talking about today. It could be that birds were the only dinosaurs to survive the extinction event because of their advanced brain features. Modern birds have proportionally larger brains compared to reptiles, ancient birds, and non-avian dinosaurs.

And as we've learned today, the brains of modern birds are highly efficient and crammed full of neurons. These traits might have given birds an edge in adapting to the fast-changing environment in the devastating wake of the asteroid. For example, their superior vision and problem-solving abilities were probably great assets.

So it might have been more than just dumb luck that allowed birds to survive. But hey, lucky for us bird enthusiasts that they did. The unique structure and organization of their brains allows birds to do all the things that delight, fascinate, and amuse us. Things like singing, dancing, fighting, raising their chicks, flying, and, at least in the case of some cheeky gulls, stealing bags of Doritos chips from convenience stores.

You've probably seen videos of this. It's pretty hilarious. You know now that the Nidopalium Cotto Laterale in the brains of those gulls, much like the prefrontal cortex in humans, helps the gulls consider the consequences of such actions in advance. You or I might end up in jail if we steal a bag of chips. But I guess the only consequences for those gulls were that they got a free meal and they became famous on the internet.

I hope you enjoyed today's episode on the anatomy of bird brains. know it can be hard to visualize all of these structures that I'm naming, so again I made what I hope is a simple diagram that might help. It's in the show notes for this episode on the Science of Birds website. If you've listened to the show before, you know that the primary way I've been able to keep making episodes like this is because of the support I get from my listeners. Specifically, the listeners who become paying members of my Patreon community. So a million and one thanks to my wonderful patrons. I want to welcome the latest additions

to my Patreon community, Fred Norman and Ranger Payne. Thanks so much to both of you for the generous support. Thank you. I also want to thank those of you who recently bumped up your support to a higher tier in Patreon.

That's amazing, and I deeply appreciate the extra help. As always, if you are interested in becoming a supporter, just check out my Patreon page by visiting patreon.com slash science of birds. I'm also generally reachable by email. My address is Ivan at scienceofbirds.com. You can shoot me a message if you want to shower me with praise

or excoriate me for being a terrible podcast host. Or if my water balloon story inspired you to confess some bad behavior you and your friends got up to as kids. This has been episode 98. You can check out the show notes for the show notes for the episode on the Science of Birds website, science of birds.com. I'm Ivan Philipson,

your humble host. I wish you a peaceful day. Cheers.