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How smart are the crows? / Brand Heinrich and Thomas Bognier

Recent experiments show that crows use logic to solve problems, and that some of their abilities are similar to those of apes and even surpass them.

Austrian crow - from Wikipedia
Austrian crow - from Wikipedia

A hunter in the North American forests sees a black crow (Corvus corax) rolls over on his back and lies down with his feet in the air next to a beaver carcass lying on the snow. A biologist laboriously climbs a rock cliff to drown crow chicks, and their parents drop stones on him from above. A lone raven makes a great noise near a distant cabin and thereby arouses a man standing near the cabin to look around and see a cougar about to pounce on him from hiding.

Each of these three men thought they knew what the ravens intended by their actions. The hunter thought that the crow was feigning death, as if it had been poisoned, to discourage other crows from competing with it for the meat of the beaver carcass. The biologist thought that the pair of crows tried, on purpose, to hit him with stones so he would go away. The man in the remote cabin thought the crow had warned him to save his life.

These hypotheses should not be ignored, but most people who have become closely acquainted with crows will perhaps offer other, more reasonable explanations. Crows are probably the most game-loving of birds, and more than once, they seem to roll over on their backs, just for fun. Many times they furiously strike the substrate below their perch when a predator approaches their nest. And it is known that sometimes they lead animals to possible prey because they cannot overcome the prey by themselves, meaning that it is possible that the bird actually led the cougar to the man.

There are plenty of stories about crows, and from many of them it can be concluded that they are very intelligent, but there is nothing in the stories to prove that their intelligence is conscious. Even behaviors, the sophistication behind which is much more visible to the eye, such as the habit of crows to cut a lump of fat into pieces so that they can carry them more easily, the way they precisely stack acorns so that they can fly with the whole stack, the way they arrange two donuts so that they can carry them both at once , and the simulated caches of food they prepare to deceive robbers, even all these do not prove that the crows are able to consciously consider possible actions and choose the most appropriate among them.

Based on the observations alone, it is impossible to rule out other explanations, such as instincts or mechanical learning of certain actions. Indeed, until the 90s, there was probably only one careful scientific study that indicated rational judgment in crows, of the kind that is taken for granted in humans. This is a series of experiments published by Otto Kohler from the Zoological Institute of Königsberg (which no longer exists) in 1943. He showed that his 10-year-old pet crow, Yakov, could count to seven by training him to fetch food from a certain vessel among several vessels whose lids were each marked with a different number of dots. But research from the last few years, most of which we both did, finally provides some conclusive evidence that crows are indeed intelligent, in the sense that they are able to use logic to solve problems. And we found to our astonishment, that they can even distinguish between one crow and another. And in this sense they are similar to humans: we would not be able to build societies (except for those similar to societies of insects) without this ability.

Proof of problem solving

The crow is not the only bird to which it is customary to attribute wisdom. In the last 20 years there has been a flood of research that has revealed that some of their relatives in the crow family (which includes crows smaller than the black crow as well as the raven, the crow, and the jackdaw) have surprising and complex mental abilities. In some species it seems that these abilities do not fall short of the abilities of great apes, and even exceed them. Cicadas, for example, have a wonderful memory that stores thousands of locations of food caches - a task that most humans would struggle to accomplish. Studies have shown that the New Caledonian crow (Corvus moneduloides) makes tools from parts of leaves of the pandanus plant and uses them to pull larvae out of tree holes. But what was not known was the extent to which these extraordinary feats involve built-in blind programming, or memorization and memory (based on past trial and error), or thinking (choosing between options represented and weighed in the mind).

We therefore designed experiments designed to isolate the roles and relative importance of each of these possibilities. In the first experiment we presented individual crows with food hanging on a wire. To get the delicacy they had to lean down from the pole they were standing on, grab the string with their beak, pull the string up, place the loop of string they pulled on the pole, step on it with enough pressure that it wouldn't slip, then let go of the beak's grip on the string and repeat this series of actions six times or more.

We found that at least some of the adult birds examined the situation for a few minutes and then performed this multi-step process in one attempt that lasted only about 30 seconds, without devoting any preliminary efforts to trial and error. In a classic design of a laboratory experiment examining the behavior of animals, each step in the desired action is rewarded with food, while incorrect steps are punished with an electric shock. The connections between the steps in the series are apparently created without the animal having to understand how each of them contributes to the final result. However, it is not possible that the birds we tested have already encountered this task in the wild, and therefore it is not possible that they learned to perform it in the past through trial and error. Therefore, the simplest explanation is that they imagined options and deduced what steps they should take.

However, success in the test required maturity. Young birds (one or two months after learning to fly) are unable to perform this complex operation. And a one-year-old bird needs an average of six minutes to solve the problem. In those six minutes, they openly try different options (for example, fly to the food, try to tear the string, peck it or pull and twist it.)

No step in the series of tug-of-wars of the crows will be rewarded with food. They had to complete the whole long series to get something to eat. One could perhaps argue that on the side of each stage there is a "mental" reward that acts as a simple positive reinforcement, because the crow sees the food approaching it, without realizing that each stage in the series brings it closer to its goal. But this explanation stands on chicken knees. If each step was learned by trial and error, many, many attempts would be needed, and learning the entire series would certainly require months of training. But it was not so. The birds seemed to know what they were doing.

However, it is impossible to know that they know unless they behave according to certain predictions. For example, if the crows knew what they were doing, they should also know what they had already done. They should have known, for example, that after raising the prize tied by the string, it was still attached to the pole. To check if they understood, we chased them off the pole after they brought up a piece of meat. If they dropped the meat, it means they knew it was attached to the pole. If they fly away with the meat (and cause it to tear from their beak), it means that they did not know. Most of them dropped the meat. On the other hand, if meat was placed on the pole to which a string was attached, which was not tied to the pole, the crows would always take it in their flight.

When you understand, there is no need, or almost no need, to conduct experiments. Learning by trial and error, on the other hand, does not require logic. We therefore asked to do another experiment to find out if the birds faced the challenge of pulling the meat through random movements that happened to have a reward on their side, but there was no logic behind them. This time we presented inexperienced birds with the same practical options, but in a situation that we hoped would make no sense to them. That is, the string was placed so that they had to pull it down To bring the food up.

Even in this situation the crows showed interest in the food. They explored the device and poked and pulled the string and thus sometimes brought it a little closer to them. But they soon gave up, and no bird learned to get the food, although the same pull-step-release sequence that had previously enabled them to get the food easily, was Can enable it again. We therefore believe that pulling straight up was learned quickly and sometimes almost "immediately" just because it was based on logic. The crows are apparently able to examine actions in their heads and imagine their results. It seems that most animals do not have such an ability, or it exists in them only to a small extent, and there is a good adaptive reason for this.

The advantages of intelligence

In a process that is still one of the great unsolved mysteries in biology, very precise behaviors can be genetically programmed even in animals with brains as small as a pinhead. Take for example the wasp that, from the day it is born, expertly produces paper and builds a nest out of it that is incredibly precise in shape, or a wasp of another species that uses mud to build a nest of clay that has a very specific shape, although different from the paper nest. Like the hornets, other species of birds are programmed to build nests whose exact nature is fixed. All barn swallows build a shelf-like nest of mud that dries and hardens. The American swallow builds oven-like nests, also made of mud but with a small, round opening.

None of these incredibly complex behaviors are acquired through learning, nor are they dependent on thinking (although learning and thinking may influence genetically programmed behavior). Thinking and logic can be very unreliable and even cause quite a stir, as we all know. If so, the big question is why there are species of animals (like us for example) that are condemned to embarrassment in logic if indeed behavior can be programmed with such precision? Why aren't we blessed, like most animals, with the ability to "act correctly" even without experiencing the multitude of possible catastrophic disruptions?

The common answer is that such animals have evolved in complex and unpredictable environments where pre-prepared responses are inadequate. When an animal is able to recognize other individuals of its species and they are also able to recognize it as a separate entity, the environment of each of them is indeed a complex environment. Therefore, researchers often see the social life of animals that are able to distinguish between individuals of their own kind as a driving force for the development of intelligence: against this background, the ability to predict the reactions of other individuals, which serve as the main relevant characteristic of the environment, becomes a very important ability. We therefore had to examine the social environment of the crows to understand how they could have benefited from intelligence more than other animals.

The natural environment of the crows

A significant part of the history of the ravens shows that they had to evolve to deal with short-term, constantly changing circumstances. Basically, crows are adaptable birds. Sometimes they hunt, but mostly they have adapted to subsist on food that other animals hunt. But the predators that provide the crows' food are unpredictable animals and can kill them too. Prolonged conditioning through trial and error seems to be unbearably expensive because the first mistake can cost the bird its life, a fully programmed response to a fickle predator can be just as dangerous.

The way in which crows compete for food also requires dealing with frequently changing circumstances. Territorial crow pairs strive to gain exclusive control over abundant sources of food, and against them, young crows and non-breeding crows employ a strategy of recruiting many members of their own kind to overpower the pair defending its territory. But it should be noted that the same behavior that gives the crowd access to food and that, due to the large number, reduces the chances of each individual being harmed, the same behavior leads to increased competition for the resource.

Predatory animals not only provide crows with abundant food sources, they also eliminate them quickly. It therefore pays for crows to be among the first in the eating circle, if possible next to the predators, while eating their prey. To do this, the birds must know the behavior of the predator, such as if and when it might attack, how far it can leap, and how it can be distracted. Some of this knowledge should be possessed by the crow before its attention is turned to eating, for in this state of affairs practice may be fatal.

Indeed, the birds train more confidently when they are young. Young birds, not concentrating on eating, often "test" the reactions of large animals, such as wolves and other predators, by coming into contact with them, usually landing nearby and pecking at their backs. This behavior does not appear to be a deliberate tactic. It is more likely to be a form of "game", which is defined in the extensive scientific literature dealing with the subject as behavior that does not serve any apparent immediate purpose, but usually has a long-term purpose, which is not consciously directed and yet pays off.

Even the young understand that tailing the predators is a dangerous game (the fear is evident in them when they do it), and hence they are probably pre-programmed for this activity because this dangerous game improves, in the end, their survival - probably by using it to learn the limits that should not be exceeded when the predators are around . With the help of this teasing, they soon learn which animals can be trusted and what is the safe distance to keep from them. On the contrary, the almost constant presence of the birds near the predators gets the larger animals used to them, and little by little they learn to ignore them. But getting along with dangerous predators is only a means to the end, which is access to a generous supply of food.

Because of the short time that an abundant food source usually remains available (a deer carcass in the woods of Maine, for example, decomposes within a day or two.) it is best to take the food elsewhere first, and eat later. The crows, like others of the crow family, store food for future use. Competing for a carcass, they diligently carry loads of meat one after the other to food caches, where they bury the meat and even disguise the hideout with waste, until it is impossible to spot. And also, again like many others of the crow family, they remember exactly where each of their many caches is, and usually collect their loot from them after a few hours to a few days. However, unlike most birds that deposit food, crows carefully observe the burial behavior of their competitors, and they memorize not only the exact locations of their own caches, but also the places where they have seen others deposit food.

Playing with food and hiding food

Since we realized that the game with the predators probably helps the crows learn to assess situations and act accordingly, we decided to check if the game really helps the young birds acquire the ability to flexibly adjust their behavior. Burying the food was an appropriate behavior for this test, and a large cage that we designed, simulating a natural environment of trees and soil, provided an adequate place to conduct the experiments.

As we already knew, we found that crows avoid the presence of others when foraging. They prefer to hide in privacy, or they use trees and rocks that hide them from others. Hoarders also try to ward off potential thieves. We found that these burrowing skills develop through innate play behaviors that provoke play opponents and allow the playing animals to learn from the reactions of their friends. This testing and learning process begins between siblings soon after they leave the nest and begin accompanying their parents, when they learn to recognize the wide variety of small edible objects, such as insects and fruit.

Young crows still in the nest, or a few days after they left it, fiddle with all kinds of objects in their beaks. And like the pinching of the wolves' tails, this behavior is defined as play because it does not yield any benefit in the short term, yet it consumes time and energy or involves taking risks. These objects are actually "toys". In the experiments we did with domesticated crows, one of us played the role of the parent and led the birds from place to place. The young birds busied themselves collecting twigs, leaves, flowers, pine cones, small stones, cigarette butts, coins and other objects that we "planted" in the field. Within a few days the young crows began to ignore, usually, the inedible items and eagerly seek out the edible ones. Thanks to the object occupation game, they experienced learning their surroundings. Since, under normal conditions, the crows' parents still feed them at this age, they could afford this seemingly pointless behavior, the benefit of which is only revealed after a while.

While the young birds are learning to distinguish between an edible and an inedible "toy", they are also improving and consolidating their nesting skills. At first, they just place some of the items that attract their attention, indiscriminately, next to other objects. Then they begin to partially hide them in crevices. And after a month or two these young birds, still dependent on their parents, begin to cover the objects with waste. Since these young crows usually deposit their hoards in front of their brothers and parents, who stay for a few months after they reach the age when they learn to fly, the other brothers often take what has been hidden. We wondered if the game of burying the inedible items helps them acquire the ability to predict how others will behave so that in the future they can hide their precious food and protect it successfully.

When testing whether experiences at a young age affect adult behavior, one of the problems that emerge is the difficulty of controlling the experiences of a particular bird, and it is difficult to build a control group for them anyway. But we noticed that the birds were also watching His son And they raided the "caches" of food that we, acting as their parents and companions, hid from them. And we can control our own behavior! In the experiment we conducted, we labeled one of us as a "thief", who always steals the objects that the young birds had buried in open play, while the other consistently examined the birds' caches of objects, but never took anything from them. In the test situation, we provided the crows, who had already grown up a bit, with food instead of inedible objects. This time one of the two people, the thief or the observer, stood by and just observed the behavior of the birds without interfering.

When the potential thief was present, the crows significantly delayed the food cache (as if waiting for the thief not to look), and the caches they had prepared earlier were emptied when the man walked by them. In contrast, the presence of the harmless human, who did not steal previously buried objects, did not delay burial, and the birds ignored him even when he approached their caches. The experiment therefore showed that the birds not only improved their food-hiding skills, after experiencing raids by others on their hoards, but they also distinguish between individuals (humans, in this case).

discriminate against the "in the know"

As we described, crows in the wild usually feed in flocks and spend a lot of time burying food for future use. In this state of affairs, it is almost impossible for any bird to chase away any other bird that happens to wander near one of its caches, which sometimes number dozens. However, adult ravens greatly reduce the possibility that their competitors will see them as scavengers, and reduce the need to expel possible robbers from the place by spreading their valuable prey over a large area of ​​many square kilometers. But inside our birdcage, no individual can escape the watchful eyes of his competitors. Thanks to these circumstances we had the opportunity to test whether the birds are able to discriminate between competing crows based on what they might know, just as they discriminated between the different individuals.

In this series of experiments we relied on the knowledge that crows differentiate between individuals of their own species (and also those who are not of their own species, like us for example). We made sure that there would be "knowing" birds, birds that saw where the caches of a given bird were, and "non-knowing" birds, those that could not possibly have seen where the caches were. Then we matched the burrowing crow with its knowing and unknowing competitors, similar to how we tested the young birds' response to thieves and non-thieves. However, in this case, the experimental design required us to make changes to the cage.

One large section of the cage was used as a dumping ground. We separated the burying section with an airtight wall from a smaller section and opened a small peephole in it, in front of which stood a pole on which a bird could stand and look through a net at the bird burying in the main section. Adjacent to the peek-a-boo section, there was a similar section that also had a bird, but the peek-a-boo window was covered with a curtain. In this way, two birds could hear the nesting bird, but only one of them could also see it.

The two crows in the small sections were allowed to enter the burial area after a short time (five minutes) and look for food there. They therefore had good reason to observe the burying crow. Indeed, the bird that knew often sat on the pole and watched the burial, and the one that didn't know, the one in the section with the curtain, tried to lift the curtain and look (it turned out that the curtain had to be tied so that they couldn't move it). After the scavenger crow had made three caches, we removed it from the large section and returned it there five minutes later to empty its food caches. We let the burrowers empty their hides when they were alone, in the presence of a knowing bird, and in the presence of an unknowing bird. (Birds of a lower status than the buryer's were chosen for these two roles, so that he would not be afraid to protect his loot from them.)

Hoarders usually pull out the food they have stored when they think it is about to be stolen. Indeed, the experiments showed that when a knowing bird was attached to the hoards, they emptied significantly more hoards than the number of hoards emptied when an unknowing bird was attached to them or when they were alone. Furthermore, when a knowing bird approached within two meters of the camouflaged food, the depositor chased it away, while when an unknowing bird did so it was ignored. We hypothesized that the cachers remembered who the birds were that were looking at them when they cached a particular cache and discriminated against them later, as if attributing knowledge to those that were looking. They seem to have anticipated the intent of the watching crow and defended themselves against the expected plunder. But the women who knew were also protected from the defensive behavior of the hoarders: they did not, in their presence, approach the hoards directly, but waited for them to move away a little. The results of this experiment indicate knowledge attribution and response prediction.

In another version of the same experiment, we sought to rule out the possibility that the informants unintentionally provided subtle cues that the impersonators could pick up and interpret, and not that the impersonators actually knew that the informants had seen them. That's why they let a man, who was standing by as a passive observer, bury the food. As we predicted based on the results of the first experiment, knowledgeable birds were quick to plunder the man-made caches when there was another knowledgeable bird in the cage with them. And in contrast, when a competitor was attached to them Dominant which knows nothing (which would attack the robber to steal her loot), they extended, on average, 10 times the time it took until they approached the cache, and waited until the dominant crow was busy and distant. These results don't entirely rule out the possibility that the raptors were giving away some subtle, unknown cues that betrayed their knowledge and caused the prey to prey, but it's unlikely that such signals were given, and the findings are pretty solid evidence that these birds display incredibly complex behavior based on the ability to interpret or anticipate the actions of others.

What are the crows thinking about?

Studying the mental states of animals, who cannot tell us what they are thinking, is fraught with difficulties. And in practice we do not know, and perhaps we will not be able to know, what is going on in the mind of another animal, and perhaps not in the minds of other individuals of our species. But if we adopt the principle of Occam's razor and adopt the simplest explanation, according to the best scientific tradition, we can conclude that the experiments we conducted provide consistent confirmation of the hypothesis that crows use some mental representation that guides their actions. The results of the tug-of-war experiments require the use of logic. And the tactics of robbery and guarding against it show that the crows remember the things that their competitors noticed and they estimate the expected threat as a result. They attribute to their competitors the ability to know, and combine this knowledge with the dominance status, to make strategic decisions about establishing food caches and emptying them.

Learning does exist, but it cannot explain all the observed behavior, because this behavior is manifested very quickly, almost immediately, without trial and error at all. We therefore hypothesize that the crows start with a game behavior pattern inherent in them from birth that produces the experience that is a necessary condition for learning. The learning may then be translated into conscious awareness, that is, the ability to use logic. Such an ability is useful in the highly unpredictable social environment of predators and competitors, and it can also be transferred and applied to any other state of affairs, such as pulling up food hanging on a string.

We don't know how unusual behavior like that of the crows is among animals. But we hypothesize that, although it is probably not rare, it is usually limited to certain types of tasks, because there is a rich variety of basic instincts and learning tendencies that are precisely adapted to the animal's living environment. However, in crows it may be more general than in most other animals. We think so because we don't know of any game-loving bird like the crow that is exposed to such a wide variety of unexpected scenarios. Perhaps thanks to these tendencies, the crows became the bird whose natural distribution is the largest in the world, a bird that inhabits the same continents as humans, and integrates easily, like them, in many different habitats.


Overview Intelligence of crows

Although the clever behavior of crows convinces most people that they are intelligent birds, there is no proof that they can consciously weigh options and choose the best of them all.

About the authors

Bernd Heinrich (Heinrich) and Thomas Bugnyar (Bugnyar) are fascinated by the intellectual skills of crows. They studied the birds together when Bognier was a research associate at the University of Vermont where Heinrich has been a professor of biology since 1980. Heinrich received his doctorate at UCLA and spent 10 years in the Department of Entomology at UC Berkeley before moving to Vermont. He authored several well-known books, including "Crows in Winter" (Simon & Schuster Publishing, 1989) and "The Mind of the Crow" (Harper-Collins Publishing, 1999) which is about to be re-released in a new edition in the summer of 2007. This is his seventh article for Scientific American. Bognier received a doctorate from the University of Vienna for research he conducted on crows at the Konrad Lorenz Research Station in Gronau, Austria. Today he is a lecturer at the School of Psychology at the University of St. Andrews in Scotland.

More on the subject

ravens, Corvus corax, Differentiate between Knowledgeable and Ignorant Competitors. Thomas Bugnyar and Bernd Heinrich in Proceedings of the Royal Society London, Series B, Vol. 272, no. 1573, pages 1641-1646; August 22, 2005.


Testing Problem Solving in Ravens: String-Pulling to Reach Food. Bernd Heinrich and Thomas Bugnyar in Ethology, Vol. 111, no. 10, pages 962-976; October 2005.


Pilfering Ravens, Corvus corax, Adjust Their Behavior to Social Context and Identity of Competitors. Thomas Bugnyar and Bernd Heinrich in Animal Cognition, Vol. 9, no. 4, pages 369-376; October 2006

The article was published with the permission of Scientific American Israel

5 תגובות

  1. An anonymous user did a similar thing with domestic cats and discovered very interesting things (despite all the pampering they get at home outside they still remain amazing carnivores)

  2. You can attach a plate to a crow or a rat and record them for several hours or a day. This can be edited as a drama series or a format called "slow TV"

  3. If crows were vegans they wouldn't reach such levels of intelligence. Lucky that vegans eat insects (accidentally) in their high vegetable diet.

  4. I wonder how it is possible to explain that they have such abilities (like a developed primate) with such a small brain?

    By the way, I haven't read the article yet, but there is a nice experiment where they put a peanut at the bottom of a narrow tube and they realize on their own that they have to fill it with water so that the peanut will float up and they can reach it.

    Here are some nice experiments that demonstrate the wisdom of crows:

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