Has a gull ever snatched a french fry from you, or made a dive at your sandwich? Would you have been more, or less, annoyed if you found out that the bird knew exactly when you would appear, and was in effect lying in wait? Scientists in Bristol, England, recently discovered that Lesser Black-backed Gulls predictably showed up at a school just before snack time and lunch, waiting in large numbers on nearby rooftops for the opportunity to snag food from the students.1 The birds were also able to visit a waste center at the appropriate time of day for freshly dumped garbage, capitalizing on weekends when people were scarce and hence less likely to disturb them. Both of these behaviors are strikingly different from the usual gull foraging techniques of actively searching for fish or other prey, and both only appear in urban gulls, illustrating how some creatures, at least, can thrive in human environments.
The gulls’ predictive ability is impressive, but it is just the latest indication of birds behaving in a manner that can only be described as intelligent. Move over chimpanzees, dolphins, and even bonobos. Apes and cetaceans doing clever things is so mid-2000s. The new geniuses are birds, especially parrots and corvids, members of the crow family. An African Grey Parrot named Alex learned about 150 words, not merely repeating them but seeming to know what they meant, and putting objects into color and size categories. When he died at the age of thirty-one, his obituary appeared in the New York Times.2 Even pigeons, birds that don’t seem like they would be thoughtful, can memorize over seven hundred different patterns, and can classify objects as either “human-made” or “natural.”
In case that seems too studious, consider Snowball, the dancing Sulphur-crested Cockatoo. This bird rocketed to YouTube fame with his ability to move along with the beat of popular songs (an article in the Guardian noted, “It all started, as some things must, with the Backstreet Boys”).3 Standing on the back of an armchair, Snowball produced fourteen distinct dance movements. The authors of a paper examining his behavior note that these were spontaneously generated by the bird, rather than copied from his owner, “who does not make a wide range of movements when dancing with Snowball and tends only to engage in head bobbing and hand waving”4 (which is an accurate description of a lot of people’s dance moves, in my experience).
Psychologists think responding to music with movement is a sophisticated form of behavior, and it is intriguing because it does not seem to be necessary for a parrot’s existence. As the 2009 paper documenting Snowball’s achievements put it, “Snowball does not dance for food or in order to mate; instead, his dancing appears to be a social behavior used to interact with human caregivers (his surrogate flock).”5 I am more than a little skeptical about this assessment, since Snowball doesn’t exactly have a lot of opportunities to mate whether he dances or not. Rhythmic movement in response to sound has also been noted in chimpanzees, which sometimes perform “rain dances” in the wild at the start of a storm.
Sulphur-crested Cockatoos have also featured in recent headlines because of a behavior that is less charming than dancing: raiding trash bins. The birds have lived in suburban Sydney for many years, coexisting with humans and eating their discarded food. A study published in 2021 by a group of researchers in Australia and at the Max Planck Institute in Germany6 used citizen science to establish that the cockatoos are not just scavenging but using complicated maneuvers to open the bins and get at the food inside. Flipping over the heavy lids of the bins requires a series of steps, from prying open the lid to walking around the edge of the bin. Only a minority of the birds have mastered this process. The technique varies among different neighborhoods, and the scientists concluded that the birds are learning how to raid trash from others, with location-specific idiosyncrasies developing as the cockatoos—that already have a rather bad-boy reputation for their raucous screams and flamboyant behavior—observe their companions.
What does it mean for birds to be able to do things that we used to attribute only to our closest relatives, like the apes, or to animals like dolphins that we already knew had outsized brains for their body size? How does a dancing cockatoo show us the folly of admitting only a select few into the club of intelligent species?
Something to Crow About
New Caledonian Crows look like your average crow, with glossy black plumage and a stout beak. They live in the forests of New Caledonia, a group of islands in the Pacific near New Zealand, and eat a wide variety of foods, including seeds and insects hidden inside dead wood and at the base of palms. In the early 1990s, biologist Gavin Hunt saw the crows using two kinds of tools to help them forage.7 In addition to using twigs with hooked ends, the birds took leaves from Pandanus trees, which look a bit like palms, and modified them, biting off bits to create a kind of saw. Both tools were employed to fish prey out of crevices.
Although tool use by chimpanzees and even a few birds had been described before, the New Caledonian Crows take things to a different level. First, they make tools that are highly consistent with each other, like a craftsman would. Second, the different tool types are shaped in a particular way, with only the narrow end of leaf tools being inserted into crevices. And lastly, the crows use the hooks to grab onto their prey and lift it out, rather than simply to poke at it. Hunt points out that this level of sophistication wasn’t seen in humans until after the lower Paleolithic era, when other aspects of material culture had already developed. Individual crows seem to learn how to manufacture tools from each other, rather than figuring out the process anew each time, something that is facilitated by them living in groups of several birds.
Since Hunt’s discovery, some of the crows have been brought into captivity and studied at universities in several parts of the world. Something of a cottage industry examining their tool use and overall cognitive ability has emerged, with titles of papers about the crows’ achievements containing phrases like “behaving optimistically” or using “mental representations.” From a behavioral biology standpoint, they read like doting parents raving about the abilities of precocious toddlers.8 Scientists house the birds in aviaries and present them with puzzles that require them to use increasingly complex tools, and do so in ways that would never be found in nature. For instance, one female named Betty took a wire and bent it into a hooked tool that could be lowered into a tube to retrieve a piece of pig heart (a favorite food), although wire is obviously not a part of the birds’ environment and she had never been shown any before. They can even use one tool to get another tool, which in turn is employed to get food, even when the eventual use of the tool isn’t apparent at the time they take it. The latter task may require the birds to mentally “picture” the outcome of their efforts, an ability that was thought by many to be restricted to humans, and is still considered to be controversial when applied to the crows.
Although they are captive, the birds seem, at least subjectively, to enjoy their tests. Betty is particularly amusing to watch in videos of the trials, as she cocks her head and industriously bends a piece of wire with her beak while holding it in her foot. One group of scientists even suggests that the birds show a “positive affective state”9—which so far as I can tell is a fancy way of saying “feel happy”—after they use tools. To prove their point, the researchers used wild crows, temporarily brought into captivity, that were trained to approach a box containing either a big reward or a small one, using the position of the box on the table as a cue for which one would be more rewarding. Unsurprisingly, they went to the box with the big reward faster. Then an “ambiguous” box—one in a new position that gave no clues about its contents—was offered. The idea is that birds that are more optimistic would go to the ambiguous box more quickly, while those that are pessimistic, expecting the worst, as it were, would either go more slowly or not bother checking the box out at all. So what makes a crow optimistic? If the scientists had allowed the birds to use tools to acquire food beforehand, they were more optimistic about the ambiguous box than if they hadn’t been using tools. It seems that something about solving a problem with external objects primed the birds to expect a more positive outcome. Whether this applies to people being more cheerful about their future after mending a bicycle or solving a crossword puzzle is unclear.
Since the New Caledonian Crows use tools in the wild, perhaps it is not all that surprising that they can extend their skills to a more artificial situation. But other species of birds can use tools in captivity even though they never do so under natural circumstances. For example, ravens, which are members of the crow family, were given a choice of objects, only one of which could be used to retrieve food from a box.10 The birds chose the appropriate tool even if they had to store the tool to be used another day. They could also use tokens that could be exchanged for food in a way that researchers claimed showed the birds’ understanding of the future, an ability previously thought to occur only in humans and apes. Some scientists have questioned this conclusion, as with the tool-to-get-a-tool research on the New Caledonian Crows, but the birds clearly have a complex understanding of the consequences of their actions.
Similar tool use by animals that don’t have tools in their environment has been investigated in Goffin’s Cockatoos, small white members of the parrot family that live in the Tanimbar Islands archipelago in Indonesia. Popular as pets, the birds’ abilities have also been studied by Alice M. I. Auersperg and her colleagues at the University of Vienna.11 Like New Caledonian Crows, the cockatoos will extract food from crevices or holes in the wild, but unlike the crows, their beaks are not very suitable for holding twigs or other items that could be used to corral prey. Nonetheless, given paper or sticks, at least some individuals will modify the material and then use this tool to fish for food that is out of reach. They will even safeguard a tool by setting it aside while not using it and returning for it later. The cockatoos can use templates, paper models in different shapes, to make a tool that matches, for example, an L-shaped piece of paper they were shown earlier. The use of templates hints at the ability to form and remember visual representations of objects, something humans are known to do but other animals generally are not. And while the Goffin’s Cockatoos weren’t specifically examined for their joie de vivre while performing tasks, the investigators point out that the birds “partake in experiments voluntarily: they are called into the experimental chamber by name,” which at least hints at enjoyment of the procedure.
The cockatoos also show us that tool use and other clever behaviors are not merely the result of contact with humans. People had wondered whether the lauded achievements of Koko the gorilla or the orcas at SeaWorld were the result of the animals’ association with their human keepers, rather than glimpses into their natural abilities. So Auersperg and her colleagues compared recently captured cockatoos in their native Indonesia with birds that came from captive stock.12 Both sets were presented with an Innovation Arena, a semicircular area that looks rather like the setup for a game show, with a different puzzle or task behind each of twenty doors. The cockatoos got twenty minutes to retrieve as many rewards as they could by doing things like turning a disc, bending a wire, or rotating a wheel.
The two groups performed equally well at the tasks, thus disproving the idea that we’re the ones making birds smart, but with one caveat. It seems that it was much harder to get the wild cockatoos to do the tests in the first place. Only three of the eight even bothered, compared with ten of eleven lab-raised birds. Although the scientists discuss at length the effect of “expectancy theories on motivation . . . and persistence during task acquisition,”13 it is tempting to be a bit anthropomorphic and simply conclude that a bird isn’t interested in doing human-devised tricks if it is used to the call of the wild.
As with the cockatoos, virtually all the studies of bird cognition find, unsurprisingly, that individual birds vary greatly in their ability to perform an assigned task. Betty ran rings around Abel, another New Caledonian Crow in the same laboratory group. The differences are unsurprising because intelligence in crows or parrots, just like in people, is a result of the interaction between genes and the environment. All Goffin’s Cockatoos are not equally adept at tool use, just as all people cannot solve a Rubik’s Cube in the same amount of time, and for at least a broadly similar reason: their experiences, their genes, and the way that the genes develop. All act in concert to produce behavior.
So why is tool use such a focus for research, and such an apparent indicator of ability? The easy answer is that manipulation of objects used to be one of those attributes that we thought set us apart from other animals. Once chimpanzees were discovered poking twigs down holes to retrieve termites, that wall began to come down. Nowadays, we know that many animals use tools, including, as I will detail in the next chapter, invertebrates. Some of them even do so spontaneously; a captive gorilla, for instance, used a stick to get peanut butter out of a plastic dome, something that observers solemnly noted “does not resemble any behaviours observed in the wild.”14
It seems that we find it particularly significant if animals behave like we do, and since we think humans are smart, that must mean they are too. But this seems unsatisfying to me; it’s as if we are creating a club with ourselves as a president and then bringing in members that we think are qualified, based on how much like us they are. Hence the early admission of chimpanzees, bonobos, and gorillas, with later membership granted to dolphins, porpoises, and, now, crows and parrots.
Does this really tell us what intelligence is, and whether it’s a quality that some animals possess and others do not? I doubt it. Behavior, remember, is not special; we could also make a club based on animals that fly and those that don’t, or animals that hibernate and those that don’t. Since we humans wouldn’t belong to either the fliers or the hibernators, perhaps it is not surprising that we have less interest in categorizing animals according to those abilities. What the extraordinary capabilities of birds—and I do not deny that they are extraordinary—tell us is that different animals with a common ancestor millions of years in the past can evolve similar solutions to common problems. It is not surprising to see birds with sophisticated behavior, because there is no reason to think that only animals closely related to humans can exhibit it.
Featherweight Brains and Assfish
Why are parrots and crows, and perhaps the occasional gull, getting so much attention? Is it that they are smarter than other animals, or is there some other reason? Part of the answer is probably a rather boring practical point: it is far easier to have corvids or parrots in an aviary than it is to maintain a captive group of cassowaries, eagles, or even many small songbirds. The birds we see as common pets are those that happen to have young that are easy to rear without the parents (or pet owner) having to foray outdoors for an endless supply of caterpillars and small spiders. Among their other virtues, baby parrots eat seeds, not insects or worse yet regurgitated carrion, which is part of why we have stories about Polly the parrot rather than Camilla the condor.
But their ease of husbandry is only part of the story. Bird watchers have noticed the clever behavior of crows and ravens in the wild for many years, and canny corvids play a central role in the folklore of many societies. Perhaps, then, these birds have some other quality that makes them more likely to be intelligent. That idea in turn leads to an examination of the brain, both in those groups of birds and in birds more generally. We know we humans have big brains, and we are smart. Does it then follow that crows have bigger brains than other groups of birds? How does that fit in with the brains of mammals, or other vertebrates?
Scientists have known for centuries that vertebrate brains vary enormously in their size relative to that of their bodies. A 1987 paper15 with the marvelous title “Acanthonus armatus, a Deep-Sea Teleost Fish with a Minute Brain and Large Ears” describes the bony-eared assfish, a creature with a brain that is less than three-tenths of a percent of its body size, thought to be the smallest brain of all vertebrates. In contrast, mice have brains that are about 5 percent of their body weight, similar to humans. Does that mean that we can safely conclude that mice are smarter than assfish (which would also make a wonderful title for a paper)? Not quite. The relationship between brain size, even as a proportion of body weight, and other attributes is complicated. For instance, shrews have quite high ratios of brain to body weight, and few have accused them of being intellectual giants.
An additional problem with assuming that larger relative brain size means greater intelligence becomes clear if you think not about comparing species, but about comparing individuals within that species. If it were always true that having a larger brain in relation to one’s body meant you were smarter, it would mean that heavier people would have a lower proportion of their body size devoted to brains than slimmer people, and hence not be as intelligent, which is obviously false.
Rather than just using brain size as a proportion of body weight, therefore, scientists sometimes measure the encephalization quotient,16 which is a way of determining relative brain size in relation to what one would predict in an animal of a given size. Imagine that you make a graph of brain size versus body size for a group of species, say mammals. Larger animals will have larger brains, and one could draw a line through the points using a mathematical formula. Some points, or species, will lie right on the line, and others will fall above or below it. The idea is that if a given species has a brain that is larger or smaller than the calculation would be expected to yield, this could provide a measure of its intelligence.
The ratio between the predicted brain size and the actual brain size is the encephalization quotient, and a large difference means that an animal has a much larger or smaller brain than one would predict from the line drawn through the points, given its body size. The quotient is not the same thing as the brain-to-body-size ratio; rather the quotient is a measure of how far a species deviates from what is expected. The encephalization quotients of mammals tend to be larger than birds or reptiles, for example. For a while scientists were busy calculating the encephalization ratios for many different animals, and found that, for instance, the quotient of a dog is higher than that of a horse, which in turn lies above that of a rat or rabbit. The measurement also yields some counterintuitive results. Gorillas, which after all are great apes like the chimpanzees, have encephalization quotients that are barely above coyotes.
Nevertheless, for a time this seemed like a way to measure something about brains that was consistent across many kinds of animals. But the quotient still turns out to be of limited use. For one thing, if you try and compare too many groups, you end up with a proverbial apples-and-oranges problem: primates and carnivores (animals like wolves and lions) both have larger relative brain sizes than cows or sheep. But if you drew a line through a group containing both the meat eaters and the vegetarians, you would end up concluding that the smaller-brained species always had lower encephalization quotients, even within monkeys or other subgroups, but they do not. What is more, finding out that different kinds of animals have higher or lower quotients really doesn’t predict performance on tests of problem-solving ability or any other characteristic of intelligence except within a very limited scale.
The big problem, however, is not that aspects of the brain, whether its size or another attribute, are unrelated to an animal’s behavior, or that idiosyncrasies of different species make comparisons difficult. It is that measurements like encephalization quotients or brain-to-body weight ratios are predicated on the notion that we will be able to rank species along a line of least to most intelligent, as though all creatures fall into order with humans (naturally) at the top, and the poor assfish—or worms or amoebae, depending on which living beings you want to include—at the bottom, and everything else somewhere in between. That assumption is part of what makes the behavior of the corvids and parrots seem so extraordinary; why would we expect birds, which by most accounts are “below” mammals in that manufactured ranking, to be such high achievers?
That hierarchical organization is a version of a scala naturae, or scale of nature, which I mentioned in chapter 2, and it is nowhere more apparent than in discussions of intelligence. As I said, we talk about animals being on an evolutionary ladder, with humans on the top rung and other species on successively lower ones, and that ladder can seem a lot like a school report card. A 2011 paper about measuring cognition in animals17 noted that more “evolved animals tend to have more cerebral cortex [a part of the brain associated with complex behavior] than less evolved animals.” As I already pointed out, animals don’t come in flavors of less or more evolved. Those cartoons of a fish that turns into a reptile that then morphs into a bird, a mammal, and finally a human being (usually a man, and usually holding a spear) imply not just change, but advancement. That reptile, one assumes, is going places the fish never dreamed of. The implicit message is that evolution produces a new-and-improved animal as time goes on, with reptiles a more advanced notion of fishes, and mammals better still—akin to the way a 2021 model car is touted as better than the 2020 version, which is better than the 2019 version, and so on. Humans are thus the end point of evolution.
As I have already explained, the scala naturae is wrong, and those cartoons do not depict the way that evolution works. The author of the 2011 article was incorrect as well, and for the same reason. Animals are not cars, and a more recently evolved species is not an improvement on one that has not changed in millions of years. By that token, microbes and viruses, which evolve rapidly, should be the pinnacle of evolution, because they have changed into new forms literally in our lifetimes.
But evolution does not have a goal or try to improve anything. Yes, those individuals with characteristics better suited to the environment leave more copies of their genes to future generations, but everything that is alive now is just as evolved as everything else. Some animals, such as cockroaches and crocodiles, look more like their ancestors than others, but evolution has been acting on them just the same. And just as your brain does not have a tiny lizard inside, the brains of birds do not represent more primitive versions of mammal brains that were improved upon when mammals, or humans, came on the scene.
The Convergent Cortex, and Teaching an Old Bird New Tricks
Back to the question of why crows and parrots are smart, whether and how their brains differ from those of other birds, and what they tell us about the evolution of intelligence. If birds do not “rank” below mammals, then what we want to know is how evolution has produced similar capacities in groups of animals that have not had a common ancestor in at least three hundred million years. Psychologist Euan Macphail declared in the 1980s that all animal species were equally intelligent, with any perceived differences among them arising simply from what that animal happened to learn.18 But that position is hard to maintain in the face of, for example, tool use by a cockatoo that has never seen a tool before and does not use one in its natural environment, compared with an animal that couldn’t use tools if you left it in a Home Depot for a year. What other than differences in ability could account for the difference in problem-solving ability between crows and, for instance, finches?
Answering that question has been difficult in part because of a lingering belief in the scala naturae. When scientists first started thinking about the way that brains were related to intelligence, or to behavior in general, they used mammals as their guide. Mammals have very particular structures in their brains that are unlike those of other animals. The cerebrum, for example, is the part that makes a brain resemble a cauliflower, and it is where the nerve cells responsible for voluntary behavior (as opposed to involuntary behavior like breathing) reside. Mammals have a part of the cerebrum, the neocortex, which was said to be the brain’s “latest and greatest achievement,” according to the Avian Brain Nomenclature Consortium,19 a group of scientists specializing in, as you might imagine, bird brains.
Thus, having a brain unlike a mammal indicated to the early researchers that an animal wasn’t smart. The problem then was that the scientists also knew that birds could do things that suggested they were at least as bright as your average lab rat, and in some cases a lot brighter. How could this contradiction be reconciled? Perhaps the problem lies not with the animals, but with how their brains were described.
What one calls different parts of the brain is a really big deal, because it has implications for the way you think about the intelligence of the creature that has that brain. The mammalian myopia of early neurobiologists gave the parts of the brain in birds different names than they did in mammals, simply because they were convinced that the birds must have the Model T version of a brain and mammals the Maserati. It turns out, however, that the parts of a bird’s brain are actually much more similar to mammal brains than had been thought. Sophisticated genetic and neurobiological analyses have allowed scientists to see connections between tissues and structures in different species. One such study examined single nerve fibers in three dimensions, a truly astonishing feat. The upshot is that what had been called a pallium, a structure supposedly unique to birds, is really akin to the neocortex, and comes from the forebrain. The consortium’s paper20 is full of jawbreaker terms (piriform cortex! palaeostriatum!), but its aim is nothing short of revolutionary: by renaming all the structures in the bird brain, we can pave the way for a new understanding of brain function and cognition.
Thus armed, let’s think in more detail about links between brain, behavior, and what we think of as intelligence. The social intelligence hypothesis was proposed a number of years ago to explain how evolution produced certain apparently exceptionally intelligent species, including humans. The idea is that the complex interactions that are a part of being in a group of other individuals selected for better memory and communication skills, and hence eventual intelligence. It is true that some more social species do better at problem-solving tests than more solitary ones. For instance, Pinyon Jays, which can travel in flocks of several hundred birds, outperform scrub jays, a set of related species that mostly lives in small groups. In primates, more social species do have bigger brains, or at least larger components of the brain associated with learning and memory, but the same doesn’t hold for birds. Thus, the Pinyon Jays may be better at cognitive tests, but they don’t have larger brains.
Many of the tests administered to animals to gauge their intelligence are themselves hard to evaluate. What does it mean to ask a crow to exchange a token for a piece of food, when they would never have to do such a thing in the wild? If an animal fails at a task in the laboratory, does that reflect more on the subject or on the test? One such study used what is called an A-not-B test, in which the subject has to figure out that the food that was in one place has been moved to another.21 New Caledonian Crows initially didn’t master the task, but it turned out that, understandably enough, that was because the birds were unused to looking at people’s hands to decipher a problem. Once they were trained to look at hands, they did as well as great apes.
A more informative approach to understanding bird intelligence comes from examining not the response to a test imposed by humans but the occurrence of behavioral flexibility and innovation in the animals’ natural lives. Maybe species that can deal with unpredictable environments have evolved more sophisticated brains with better cognition. But how to test that idea? Canadian biologist Louis Lefebvre hit on a clever solution: take advantage of bird watchers’ obsession with reporting on peculiar behaviors in the species that they see, or, more accurately, of the willingness of scientific journals that specialize on birds to publish said reports. For instance, if a researcher saw a grackle, not ordinarily a predatory bird, kill a Barn Swallow, as P. LaPorte did in 1974, or a magpie eating potatoes, as noted G. G. Buzzard (no, I am not making this up) in 1989, the observation could be written up as a short note and published.
Using such notes from journals in North America and the United Kingdom, Lefebvre and his colleagues catalogued the species involved,22 and confined their analysis to items where the authors used words like “opportunistic,” “novel,” and “unusual.” Out of nearly six thousand short notes, they gleaned 322 examples of innovations having to do with feeding, whether that was eating unusual items or finding them in a novel way, as with the grackle. They then looked at the relationship between the species that were seen innovating and their forebrain size, taking into account body size and a few other characteristics. It turned out that the birds that were more likely to innovate also had larger forebrains, consistent with the idea that behavioral flexibility is linked to a measure of intelligence. An even larger study by Lefebvre and Nektaria Nicolakakis,23 with 683 innovations published over thirty years, included nesting oddities (a kingfisher building its nest in peat cuttings in England, rather than the usual cavity along a riverbank) as well as feeding innovations. The unusual nesting behaviors were not found more often in species of birds with bigger forebrains, but, as before, the feeding innovations were, supporting the earlier claim.
The latest version of this line of research took an even broader view. If behavioral flexibility is an indicator of one’s ability to adjust to a changing environment, then in the long term, maybe species more capable of coping with such changes will be more likely to survive. Simon Ducatez from the Center for Research on Ecology and Forestry Applications in Barcelona, Spain, led a group of scientists including Lefebvre to see if species that were more likely to eat unusual foods were less likely to have gone extinct.24
Once again, the researchers trawled the ornithological journals, this time accumulating more than 3,800 observations of over 8,000 bird species from all over the world. They matched the occasions of innovation with the classification of extinction risk for each species by the International Union for Conservation of Nature, which keeps a Red List of all threatened species. In a paper published in 2020,25 the scientists showed that innovative species were gauged as less likely to go extinct in the wild. The innovations were many and varied, including the Rufous Treepie of India that has taken to eating candles made of wax and clarified butter that are left at temples; they will even grab the candles while the wicks are still lit. Although a willingness to eat unlikely seeming foods is not the only thing influencing extinction, the study illustrates what being smart might really mean in nature.
On the opposite side of the spectrum from extinction is speciation, the formation of new species from ancestral forms. Some groups of animals seem to do this much quicker than others. The world contains lots of different kinds of jays and sparrows, and not so many emus or ostriches, for example. All birds come from a common ancestor, but after that, some of the branches on the evolutionary tree evolved many more twigs than others. Here, too, brain size seems to play a role. Using information about the ancestry of more than 1,900 bird species, a group of researchers from Sweden, Spain, and Canada showed26 that the large-brained lineages were likelier to have split up into many different species over time. What this means is that behavior, perhaps in the form of problem-solving ability, flexible response to the environment, or even social skills can affect how fast evolution happens.
Live Long and Wisely
If having a big brain is so advantageous, why don’t all birds, or all animals, possess one? The answer is that brain tissue is expensive, requiring much of the energy an animal’s body acquires to sustain it. Brain size, then, like most other characteristics, is a trade-off between the cost of maintaining the organ and the benefits it conveys to its bearers. If you are a human, the benefits of a large brain seem obvious, but why should a crow or a chimpanzee or a parrot have evolved a large brain? The cognitive buffer hypothesis27 was developed several decades ago to explain why. According to this idea, big brains allow animals to live longer in environments that change quickly; hence the relationship between brain size and behavioral flexibility. The hypothesis means that we should also see bigger brains in longer-lived species that are in variable environments. But how can we test this idea?
Recent advances in the analysis of very large data sets containing information about many hundreds or even thousands of species, combined with information about the environment gleaned from remote-sensing technologies, has given some clues about how to solve this problem. Using satellite data from NASA on environmental variation in many parts of the globe, a group of scientists matched up brain size (suitably corrected for body size and a few other potential complications) in 1,200 bird species with whether the bird lived in a place with extreme seasonal fluctuations, or in a place where the plant cover changes a great deal during the year.28 So, for instance, places with a lot of snow, and hence less plant cover, require their inhabitants to figure out how to get food during short days and under difficult conditions. Species with large brains were indeed more common in places where the environment is more variable, though it is not clear whether big-brained species were more likely to move to such places or whether selection caused birds already living in variable habitats to evolve larger brains.
What about the big brains and longevity part of the hypothesis? Here, too, the ability to use “big data” amassed from a variety of sources was put to use. Like other animals, different bird species vary in how long they live; parrots, for example, can live for decades, while many songbirds are lucky if they make it through three or four years. A 2020 study29 examined 339 bird species, including both those that have young requiring a long period of care in the nest, like parrots, and those that produce chicks able to walk and feed themselves immediately after hatching, like ducks and many shorebirds. Within both groups, the species with bigger brains lived longer. What is more, parrots seem to have specific genes that are associated with longer lifespans, including those that improve immunity and help repair damaged DNA.
Interestingly, the longer-lived and bigger-brained species also tend to lay relatively larger eggs, which suggests they put more into their offspring, since larger eggs have more nutrients to give the chicks a head start in life. That fits in nicely with yet another study of bird cognition, one focusing on the crow family. As I mentioned earlier, brain tissue is expensive, and species with advanced cognitive abilities, whether crows or humans, require a long time to develop their skills, time that is generally spent in the nest (or house). Maybe, then, having an extended period of parenting facilitates being intelligent. As we have seen, corvids in general are good at solving problems, but not all crows and jays are alike. Siberian Jays, for example, are, as their name suggests, residents of a large part of the Palearctic. They live in small groups of a breeding pair, the offspring from previous years, and occasionally some unrelated individuals. The offspring can stay with their parents for up to four years, an astonishingly long time for a bird. The lingering childhood has been attributed to the high risk of predation by Northern Goshawks, which particularly target young birds. The goshawks are deterred, however, by mobbing, a group behavior that is exactly what it sounds like: several jays surround the hawk and dive-bomb it, chasing it away from their territory. Learning how to mob requires the role model of a parent, and a lot of observation. New Caledonian Crows also can spend several years with their parents, though in their case the young are busy learning how to make and use the palm leaf tools that they employ to get insects out of trees. In both cases, prolonged adolescence helps the young get a good start in life, and it is possible that in both humans and the corvids, extended parenting is key to the link between big brains, long life, and an unpredictable environment.
On, or Off, the Wall
Tool use is only one of the classic markers of animal intelligence that have been used over the years. Another one is the mirror test, mentioned in chapter 4, in which researchers place a visible mark on an animal and then show the animal its reflection in a mirror. If you do this with a chimpanzee, it will poke at the place where the mark appears, which implies that they recognize that what they see is a version of themselves. Since its development by psychologist Gordon Gallup Jr. in 1970, the test has been employed in many animals.30 In addition to chimps, orangutans, Asian elephants, and Eurasian Magpies have passed the mirror test. Some scientists have concluded that it shows a strong relationship with encephalization quotient, and hence is an indicator of greater intelligence.
The problem is that other species you would expect to excel at this test, like some monkeys, crows, gorillas, and even (depending on the circumstances) some children, flunk it. As previously mentioned, some researchers suggest that since dogs don’t use vision, a kind of mirror smell test would be more appropriate for our canine companions. It turns out that dogs can distinguish their own urine odor from that of others, and that they pay particular attention to their urine if it is altered by an unfamiliar scent—a kind of olfactory poking at the forehead spot when it’s seen in a mirror. But does that mean the dogs know who they are? The discussion continues, with a 2019 paper31 even suggesting that cleaner fish, the kind that groom the parasites off other fish species, can recognize themselves in a mirror. If that result holds up, they would be the only animal other than a mammal or bird to do so.
Eminent primatologist Frans de Waal says that it’s hard to know whether the mirror test indicates self-awareness, in part because this is not an all-or-nothing capacity, with some animals crossing the gulf to awareness and others simply not reaching it. I agree; the fallacy of the scala naturae tells us that we can’t put animals—or any other living thing—into simple bins where some have achieved an ability and others have not. De Waal then says,32 “We need to start thinking more along the lines of a gradual scale.” Here I would go a step further. Even a gradual scale implies that we are all arrayed along a line, where, just as the scala naturae would have it, one form leads to the next and the next. It suggests someone is at one end, and someone else is at the other. But evolution doesn’t form a line, it creates a bush, with messy, branching stems and long distances between groups that then evolve similar properties. The animals, including us, do similar things because selection has acted on us in similar ways, not because of our ancient mutual ancestor. Hence the extraordinary capacities of corvids, parrots, and many other animals that are not closely related to humans.
If You’re So Smart . . .
Of course, behavioral flexibility and toolmaking are not automatically the same thing as intelligence. Humans are pretty flexible, and we use tools, so we tend to look favorably on other animals that do the same. But defining animals that are similar to us as intelligent simply because we think we’re intelligent is circular, to say the least. And as we will see in the next chapter, even insects, which have often been dismissed as robotic automatons incapable of true intelligence, can show remarkable feats of learning. What the clever actions of the birds illustrate is that we do not have just two choices: animals that are just like us, or animals that are simple machines incapable of any intelligence at all. Instead, birds have evolved similar behaviors through alternative pathways. Starting as dinosaurs—and birds really are dinosaurs, after all—they met challenges in their environments with flexibility, just as some other animals, including some primates, did.
This realization also gets us away from the game-show contestant view of animal intelligence, in which we try to rate animals for how smart they are. We don’t try to rank animals based on their kidney function (though, seriously, kangaroo rats can exist without ever drinking water, which is a fairly amazing feat). Why should we try to do so on the basis of intelligence? Yet the desire never seems to go away. A paper33 published in 2019 by an astrobiologist from the Technical University Berlin posited that we should look to naked mole rats as harboring latent capacity for getting on the list of smart animals.
Naked mole rats are rodents, as you might expect, and whatever you think of their intelligence, they would never win any contests for beauty. Hairless, as the name suggests, with elongated front teeth they use for digging, mole rats live in colonies underground, feeding on roots and tubers and defending their groups against the burrowing snakes that are their main predators. They have been the subject of much study because they have social systems akin to those of bees and wasps, with a queen that produces all the offspring and workers that take care of them. The author of the paper seems quite taken with the creatures, suggesting that their “active lifestyle” and “hygienic behavior” are “feature[s] of intelligent organisms,”34 noting approvingly that they defecate and urinate in designated areas. He does note regretfully that mole rats have poor dexterity, and that they lack the ability to use fire, which on further reflection seems not a bug but a feature, given how difficult it would be to control flames in underground tunnels. The paper concludes by wondering if the naked mole rat “may progress toward truly advanced intelligence.”
While naked mole rats are an oddball candidate for the next intelligent creature to follow crows or parrots, an enthusiasm for them points to the futility of trying to array animals as if the world was a giant SAT test. Mole rats are, indeed, good at being mole rats, but that doesn’t mean they win some global contest. The crowdsourced question and answer site Quora recently featured the query, “Why is there only one intelligent species? Why aren’t other species intelligent?”35 The answers range from “Human brains would be wasted in other animals” (which begs the question of whether they are wasted on us, too, and who is doing the wasting) to “If you interpret the definition of ‘intelligence’ broadly enough, you can assign it to a jellyfish too” to “Mice are intelligent at mouse stuff” to “We got lucky.” This last is debatable, but certainly the answers point to the realization that animal intelligence may be more complicated than is sometimes realized.
And speaking of being intelligent at mouse stuff, it’s worth noting that there may be hope for rodents, which have never been on anyone’s list of Most Intelligent. One of my colleagues at the University of Minnesota, Emilie Snell-Rood, led a study36 comparing the size of brains in mice caught in urban environments with their counterparts of the same species collected in rural areas. The results attracted the attention of the National Public Radio show Wait Wait . . . Don’t Tell Me!, in which listeners can call in to participate in a limerick fill-in-the-blank contest based on the week’s news. In August of 2013, one of the limericks was as follows:
Not just must we run from the kitty
but we must seem urbane and quite witty.
A quaint rustic charm might do well on a farm
but we mice smarten up in the . . .
Listener Stephanie Garber from Florida correctly guessed that the missing word was “city.” The host of the show, Peter Sagal, accurately summed up the study, saying, “Biologists at the University of Minnesota have found that city mice have bigger brains than their country cousins. That’s because they say city mice have more to adapt to. In the country, it’s Tom and Jerry, in the city it’s Tom, Jerry, and Crazy Hobo with a Gun.” This is not exactly how Emilie and her coauthor Naomi Wick put it, but it is reasonably accurate. The mice collected in urban areas indeed had bigger brains, which the scientists suggest arose because the greater levels of variability in cities selected for behavioral flexibility. Mice that could cope with more novelty in their environments did better and had more offspring than their counterparts that were in a more predictable habitat. Sagal went on to say, “The worst part is that city mice are also elitists, out of touch with real American mice. They only eat trash from Whole Foods.” I have no comment on that.