Mind of the Raven: Investigations and Adventures With Wolf-Birds (40 page)

Two days later, I introduced two round, white PCV drainage tubes into the aviary, four feet long and four inches in diameter. The tube was a different kind than ones I had used in previous experiments. As they always do with new objects, both birds inspected this new tubing from up on their perches, craning their heads down, twisting and turning their heads rapidly. Fuzz made deep rasping caws, a normal response to feared predators or strange things. Then he came down to make an inspection. He stood sleek and tall, and jumped nervously all around the tube as if performing a dance. He leaned down with his head close to the ground and peered into one end. He walked the four feet to the other end and peered in from that end also. Houdi meanwhile watched him from her perch. When he had finished and had gone back up to the perch, she joined him without examining the tube herself. I left the tube, being satisfied that they knew or would soon learn that it was hollow, not a white log.

In the meantime, I had introduced them to snakes. They had learned that snakes are good to eat and that they slither. Weeks later, I brought a live, foot-long green snake. Holding it by the tip of the tail,
I dangled it in front of the white PVC. Then I dropped it. The snake slithered into the tube, and I stepped back. Both ravens had been watching me from their perches thirty feet away. Fuzz came down, walked to the mouth of the tube, looked in, then hopped rapidly the whole four feet around to the other side. He reached in, pulled the snake out, crushed its head, fed from it, and cached the rest, covering it with leaves. Houdi watched. A few minutes later, she went to Fuzz’s cache, retrieved the remains of his snake, and ate her fill also. Fuzz tolerated the theft because they were a pair by then, and he wasn’t very hungry. Later, with another group of birds, I dropped food into the same tube, now held up vertically. In that case, when I dropped food in front of them, instead of looking first from the perch at the end where they saw me put the food, they hopped down to the ground and went on their first try to the end where the food had ended up (snug on the ground and where it could not be seen except after digging). That is, they had anticipated its movement through the tube.

I wrapped a lump of butter in paper as the ravens watched me, and put it into the tube, stuffing wads of green foliage behind it. Fuzz did not hesitate to pull out all the foliage to get the butter. I then put an egg in so far that it could not be reached from either end. Fuzz checked into the tube from both ends, walking back and forth, for a total of eight inspections, first at one end and then at the other, as if not believing that what could be seen at one end could not be reached from the other. After the eighth look, he finally picked up one end of the tube. The egg rolled out, and he ate the yolk. One explanation for him picking up the tube might have been that in frustration he would try almost anything. Another is that he knew the egg would roll out. Not all apparently deliberate acts are as ambiguous.

A pair of wild ravens on the frozen carcass in front of my spruce blind were chipping little pieces of meat off one at a time by partially opening their bills and using the pointed tips of their lower mandibles as chisels backed by the force of the momentum of their swinging heads. In contrast, they pulled off softer meat in small chunks by grasping and pulling, using the small hook at the tip of the upper bill. Chunks
of meat were stacked piece by piece into a pile. Finally, the birds grabbed their whole pile and flew off with it.

Ravens in crowds always act differently than those alone or in pairs. They never stack meat, perhaps knowing that any loose piece would instantly be taken by another bird. They instead either fly off with only one large piece at a time as soon as they have detached it, or fill their throat pouch with small pieces before flying off.

A large chunk of beef suet in the woods in the back of my house could not be pulled apart into pieces like meat. The frost-hardened suet could, however, be handled by hacking into it, chipping off small, loose pieces similar to how woodpeckers, crows, blue jays, chickadees, and nuthatches invariably do it. Ravens normally feed on suet in this way as well. But one day, one raven did something imaginatively different.

The raven pair that fed there never allowed me to get close. They flew off even when they saw me near a window. I had gone to the food at the edge of the woods, as usual, to provide new food, and as I started to walk there, the raven that had been feeding flew up. I had not observed its feeding behavior directly, but it had left its tracks in the snow. Most interestingly, it had also left an intriguing record of what it had done. This bird, rather than randomly picking off small chips for immediate eating, had carved a groove around one corner of the fat. This groove was carved using precisely aimed blows. The object had obviously been to cut off a manageable chunk from a larger, immovable one. Many of the small pieces of fat that had been chipped off during the cut were not even ingested.

I want to indicate briefly why I was so excited about the seemingly trivial fact of a raven carving a groove in fat, when birds are capable of infinitely more complex innate behavior, such as weaving ornate nests or navigating by sun-compass, using an internal clock. That the raven had carved the groove was a fact, and given that no other birds and perhaps only a very rare raven would do such a thing, it was a highly singular fact. One robin does not make a spring, but this one fact was visible proof that the bird had forgone immediate gratification for a reward later on. That’s planning. There were no secret raven trainers
out there in the woods, it was not a learned plan. It was a plan derived from mental visualization. It was an invention. It made the raven’s life easier but was hardly necessary. Given the constraints of the alternative interpretations, what the raven had done was news. I felt it should be splashed across the front cover of
Nature
and
Science
. Of course I knew it would not be. As expected, it was rejected several times for publication because it was “just an anecdote.” Science, to be publishable, is almost defined as that which is strictly replicable, and there was no way that anyone could drop off a hunk of suet and expect a raven to slice a piece off by hacking a groove through it. Not even my aviary birds would do it. This was a raven Einstein.

The record of peck marks in the suet seemed to suggest that the raven not only had thought ahead, but also had acted on that thought and shown intelligence. Intelligence is not merely consciousness or awareness alone. It is not just complex behavior. Intelligence is not just super-detailed memory, rapid learning, complex vocal communication, play behavior, or tool use. Intelligence may or may not be related to all of these things, and some kinds of intelligence require them, but they are not what intelligence
is
. Intelligence is doing the right thing under a novel situation, precisely as this bird had done. Intelligence is understanding the world, and reacting appropriately to it, not just perceiving it. Intelligence is about awareness, and about testing responses in the head rather than the “real” world, where such activity may be time-consuming, harmful, or fatal.

R
AVENS HAVE RELATIVELY LARGE
brains, and they do many things that look intelligent, but there was still no experimental proof that they
are
intelligent. I needed new ideas to get out of a rut, but really new, novel ideas, seldom come to us by forethought or design. They come by mucking around even as we try not to. I got my idea for a new approach on examining raven intelligence by leafing through a copy of
Ranger Rick
magazine, a present to my then young son, Stuart.

The magazine contained a short article on the “clever” things you can watch birds do, like pulling up food suspended by a string. I could not believe that chickadees could actually do that. If they did, it seemed to me, they would have to be trained. And if you trained them first, then insight or mental visualization needed to perform the task could follow the task, but could not precede it. I dismissed the whole
“intelligence” aspect of this, as I had with so many other stories I had heard.

My next thought was that if ravens were as intelligent as they sometimes seemed to be, it was possible that a rare individual among them might figure out how to pull up food on a string without having to go through lengthy trial-and-error learning. That is, insight might precede or accompany learning to produce the same behavior. The bird might evaluate the situation, play out a mental scenario in its mind, and from that insight perform the task quickly.

Testing experimentally for the existence of insight—the evaluation of different choices to make an intelligent decision without overtly trying them—may seem impossible to do because everything that an animal does includes prewired responses and learning. Neither of these can be simply excised from its brain.

Any one behavior is a combination of innate programming of blind or unconscious responses, learning, and insight. For example, our sexual preferences are largely innate, but giving flowers during courtship—preferably daisies rather than skunk cabbages—takes insight as modified by learning. There is no apparent limit to the complexity of animal behavior that can be innate or learned, provided it relates to the same conditions the animal has encountered predictably over millions of years. Insight requires consciousness, but it is more. It is the mental visualization of alternative choices that then guide judgment of new situations at the moment. It could be common in all sorts of behavior, but we can only
assign
it to play a likely role in behavior when it fulfills three criteria: First, to eliminate the innate component, it has to be extremely rare and
exclusive
of what the animal normally encounters and does. Second, it has to solve a problem. Third, it can’t be a learned response.

In the wild, ravens’ food is never found dangling on anything that resembles a string. String-pulling could therefore not be hard-wired into the innate behavioral repertoire by natural selection over millions of years of foraging experience. The behavior might, of course, be learned in incremented steps by tedious repetition where you reward the first step that contributes to the correct solution, then you reward the
second step, and so on until the bird ultimately strings together a dozen or more steps. My captive ravens had never before even seen string. I had a unique opportunity to do a useful experiment. I doubted they could perform the task, but if they did, then innate programming or learning could both largely be excluded, leaving either insight or random chance as the prime contender for an explanation.

As I contemplated the problem of how a bird would get food dangling from a string, I saw a unique opportunity for testing insight, a mental capacity that defines at least one of several proposed kinds of intelligence (Gardner, 1998). First, food should give a strong emotional motivation to induce a bird to try to get the food the easiest, quickest way. The bird might try to sever the string, fly at the food directly, or attempt to knock the food off. Yet, given a secure string, there was only one sure and easy way to get the food—pull it up in successive steps, hanging on to each pulled-up loop of string.

Pulling up food dangled on a string involves many steps that must be executed in a precise and nonarbitrary sequence. The bird must 1) perch above the dangled string that is attached to the food, 2) reach down below the perch, 3) grasp the string with its bill, 4) pull the string up and over the perch, 5) place the pulled-up loop on the perch, 6) lift one foot, 7) step on the loop of pulled-up string with the lifted foot, 8) press down with the foot hard enough to prevent string slippage, 9) release the bill’s hold on the string, but only after the foot is already firmly pressing the string down on the perch, and 10) repeat the whole sequence a variable number of times depending on the length of the string and the amount of slippage of the string.

I arbitrarily chose a string length of two and a half feet because I felt it would present the birds with a sufficiently challenging problem. The process would have to be precisely repeated at least five to six times, or perhaps many more times if the string were to slip. In all, dozens of discrete steps had to be assembled into one precise sequence needing constant updating as it progressed. Any one step by itself could of course be learned and/or innate, but the critical behavior was not any one individual step or steps. Instead, it was the placing of these steps into a unique sequence that would solve a unique problem.
It was practically implausible that the correct sequence of dozens of discrete steps would emerge by random chance.

The beauty of the string-pulling test was that 1) it greatly reduced the possibility that the solution could be arrived at by random chance, 2) there was no plausible genetic programming that could have coded this very specific unnatural behavior because there is no conceivable reason for it to have evolved in the wild, and 3) my ravens had been hand-reared in captivity in an aviary and had no experience in string-pulling. They had not even seen string, hence, I knew they could not have had prior opportunity to learn the behavior.

My ravens, I presumed, would not be able to get meat by pulling it up on the string. If they did not, so what? Nothing would have been lost. On the other hand, if they did it from the start, a lot would be won. Invoking Occam’s razor, the rule in science that favors the simpler theory over the more complex one, a successful pull-up would suggest that the birds could solve a problem. That’s proof of insight and if one grants it is a difficult problem, then its solution is also a measure of intelligence as regards that problem. Furthermore, solving the problem by insight presupposes consciousness. And all I needed for this was a piece of string and a slice of meat—not exactly an impressive investment. It was worth the try.

When I first thought about doing the experiment, I recognized two complications. First, ravens are highly temperamental animals. They would be wary of the string. In one test out in the field, I hung a piece of meat on a white piece of twine from a branch next to a rock-solid frozen cow carcass where more than fifty wild ravens were feeding at temperatures near minus 25 degrees Fahrenheit. They had to work long and hard to chip off tiny bits of meat from the carcass, and every dawn the crowd came and all chipped for hours. Any
loose
piece of meat was a valuable prize, to be taken instantly and much fought over. So here was suddenly a morsel of choice food dangled next to them. What happened?

I was as usual well hidden in my blind of spruce and fir. I had put up the meat while it was still dark. At dawn, the birds came and instead of quickly descending to feed as they usually did, they stayed up in the trees, making angry, rasping alarm calls such as they make
to strange, frightening phenomena. Only about an hour later did one of them descend to the cow, leading the others in. They looked at the meat on the string as if it were an apparition. Not one went near it. I left it there. Two days later, it was still there.

I hoped that my aviary birds would be less spooked by such a strange thing, but I expected that they would be shy, since they had never seen or experienced food on string. If they did figure out a solution to reach the meat, they still might not demonstrate their insight because of fear of approaching the string. Ideally, I would test them one at a time, but that meant catching them and building another aviary to isolate them, which would cause much disruption, money, and time. Isolated aviary birds would likely stay away for days from something as unusual as food dangling on a string. The ravens would be much calmer if they remained together as a group. There was a negative aspect to working with a group of birds, because if one pulled up food, the others might simply copy the first, and/or chase away all others. Nevertheless, the first bird I tested had none other to copy, and I was interested in the phenomenon as such rather than in how many individuals could or could not do it. It made no difference to me whether ninety-nine percent or one percent of the population of ravens could solve the problem. If problem-solving—whether you choose to call it genius (in ravens), insight, or intelligence—proved to be present even in one bird, then it exists. Even if rare, it is no less interesting a phenomenon.

Hard salami was important for my test. I first offered pieces out of my hand to make sure they would want it; they ate it eagerly. I knew if I had used soft meat and a bird had flown at the suspended prize, grabbing it with its bill, it might have torn off a small piece. Being rewarded, the bird would be predisposed to try the same maneuver again and again; it would not find it necessary to try anything different. Hence my test would fail.

The salami was three months old, having dried in the refrigerator to a leather-like consistency. The ravens would not be able to tear it off by flying at it, grabbing it with their bills, and then dangling from it by holding on to it with their bill, behaviors I was sure they would try if they tried anything.

I notched a slice of salami and tied it onto the end of tough woven string, then tied that onto one of the horizontal perches in the aviary so that the prized food item was suspended about six feet off the ground and two and a half feet down from the perch. I rushed back into the house to my desk by the window to watch.

All of the birds looked at this new thing. The dominant pair came closer and tilted their heads and stared at the salami. They looked at the string wound round the perch, then hopped up and down on the perch doing nervous jumping jacks, as they would do in front of a feared carcass. The string and the salami jiggled. After a while, and more looking, they cautiously approached. One of them pecked at the loop of string tied around the perch and quickly jumped back. They kept craning their necks to look down. One gave the string a few tugs as if trying to rip it off the branch. The meat jiggled some more, but the string was tough and did not break. The birds then seemed to lose interest. I went back out to remove the string with the salami. I would have them try it again some other day. “Just what I expected,” I thought. “No way will these birds get that meat.”

When I put the meat out the second time the two birds again eyed it warily, but looked less nervous than the first time. Abruptly, one of the birds, Matt, flew up to it, and to my utter amazement performed the entire sequence with only minor fumbling. I shouted for joy and pounded on the window to startle him so he would drop the food. I wanted to make sure his reward was only mental. Not having eaten, would he go through the entire sequence again right off?

This bird knew very well what he had done. After I shooed him off, he returned within several seconds, pulling the meat up in great haste. Again and again (six times) I chased him off before he had a chance to eat. Interestingly, he never tried to fly off with the salami after pulling it up. Furthermore, he always dropped it even when I rudely startled him and later when I literally had to push him off his perch after a meat pull-up when he held the meat in his bill. In contrast, when the birds get a piece of loose meat they
always
fly off with it.

After the sixth repeat of the pull-up behavior, I knew it had not been a fluke. Matt really did know how to pull up meat. As a reward
after all those “empty” repeats, I finally allowed him to eat salami. My reward was an adrenaline rush, and the chance to do a series of experiments that built on these original observations. I was hooked. I was convinced that I had blundered upon an insight for testing insight in ravens.

Eventually, I saw other naive ravens do the pull-up of the same length in as little as six minutes from the time of first presentation of the meat on string into the aviary, and after as little as thirty seconds after they first contacted the string. Given that many of the birds were shy of strings, the time required to pull up the meat successfully probably greatly underestimates the amount of time it takes them to do the task, after they see meat on string. The presence of the other birds turned out to be a big problem (which I solved in another set of observations with another group of birds) because whenever a dominant bird who knew how to pull up meat saw a subordinate near meat on string, it tried to chase the bird off.

I eventually tested five different groups of ravens and two crows. In no case did any naive birds ever show any interest in pulling up, or even approaching a string without food attached to it. In all groups of ravens, but not the crows, several individuals performed the whole sequence with little or no fumbling right from the start. Two patterns were seen. In one pattern, the “direct pull-up,” the bird stayed in place to pull up successive loops carefully, stepping as the loops pulled up. In the other, the “side-step,” the bird pulled string laterally onto the perch before stepping on it, then pulling up again, and so on. On the other hand, a group of four three-month-old ravens, like the two crows, were incapable of reaching the meat, although they showed no fear.

To me, the most convincing point of the experiments that showed insight (because it excluded both observational learning and trial-and-error learning) was that those birds who didn’t pull up meat, but who seized meat on a string that I or another bird had pulled up, tried to fly off again and again with that meat. Of course, since it was still attached to the string, it was rudely yanked out of their bills. They didn’t seem to catch on until at least six trials. Those birds who
did
pull the meat up, on the other hand, never once in thousands of trials
flew off with it so long as they were left on their own. I had difficulty shooing them off the perch after they had pulled up the meat, and when I did succeed in getting them to leave, they almost always dropped their piece of meat before flying off. The ravens that had pulled up the meat acted as if they knew, from the very first time they pulled it up, that to try to fly off with the meat would involve having it ripped out of their bill in flight. The significance of the remarkable behavior of
not
flying off was that it was a
new
behavior that was acquired without any learning trials. They acted as though they had already done the trials. The simplest hypothesis is that they had—in their heads.