Mind of the Raven: Investigations and Adventures With Wolf-Birds (33 page)

Unlike the pair that McEneaney watched and the many pairs I also have watched, ravens in
crowds
in the field almost always cache food very far from where they get it. I have seen ravens from these crowds in the wild make many thousands of caching trips, but I’ve seldom seen them actually make a cache. Most likely, the ravens near the food pile do not get to see others making caches, either. That’s probably no accident. Ravens may have to make their caches far enough
away so that other ravens don’t find them. Watching from the top of a tree, as a raven might, I sometimes see the birds carrying meat fly off out of sight, over the next ridge, down the valleys. When I’ve found cache sites—tracks and scrapes in the snow—it has been only by walking at random in the woods. Caching close to a carcass not only invites thieving by other ravens, it also poses another danger. Such keen-scented carnivore scavengers as coyotes, fox, fisher, raccoon, and weasel, as well as other animals from bumblebees to squirrels, concentrate their search for food near where they previously have been successful. That is, if dozens of ravens put their caches in the same area, all the caches would be in greater jeopardy than if they were spread out.

All of my observations of raven-caching behavior indicated more flexibility than had ever been observed in any other animal. I wanted to get publishable results, and turned to more experimental conditions for a tighter focus on specific aspects of the caching behavior, such as memory, using fifteen individually identified wild-caught birds who were kept in one of the side areas of the aviary off the main complex. From this pool of birds, I would capture from two to four birds at a time and place them into a second side area of the aviary. Continuously well fed birds don’t cache food (Gwinner, 1965), so I kept them without food for two days to induce the caching response. After the two days, they were allowed into the large experimental enclosure where a pile of chopped meat chunks had been placed on the snow. Up to an hour commonly elapsed before the birds ventured to contact the food, but after they did, they usually began caching immediately. I allowed them another half hour of feeding and caching, then chased them back to their side aviary. I waited for different durations, from one day to one month, before I would let them back into the experimental area to see if they could recover their caches. If the memory interval to be tested was more than two days, the birds had to be fed in the meantime, and then again allowed to go without food for two days before the retrieval part of the experiment, so that they would be motivated to recover caches.

I found that the birds easily remembered caches made a day or two before. They had poor ability to remember caches made two weeks
earlier, and they were virtually unable to recover month-old caches. As usual, some of the details of these experiments, which I began in February 1992, were more interesting than the general results.

In one experiment, White Slash and Blue Diamond (names referring to symbols painted on wing tags, which I’ll here shorten to Slash and Diamond) were allowed on February 4 to feed and to make caches. For the first two and a half hours, Slash spent most of her time flying about. She fearfully approached the bait—chopped pork lung—dozens of times, doing jumping jacks with her bill open in fright. Finally, she edged close enough to grab a piece. Diamond had perched nonchalantly during that time, but after Slash got a piece of meat, he suddenly became active. He followed her as she fed briefly. She eventually cached her piece of meat, but not until Diamond was almost but not quite out of sight at the opposite end of the aviary. Immediately after Slash cached, Diamond flew over and dug in the snow at her cache site for three minutes. The snow was deep, and he apparently had not watched closely enough to succeed in recovering Slash’s cache. A few minutes later, Slash herself showed no problem recovering her own cache. She then continued feeding.

I left them without food for another day, hoping they would become more motivated to make multiple caches. In the morning session, they both acted uninterested in the pile of chopped pork lung. In the afternoon, Slash approached the meat within one minute after I put it down. She fed, and then again made a cache in the snow. As on the previous day, Diamond immediately flew there to dig. Strangely, Slash did not intervene. Instead, as Blue was preoccupied in trying to dig up her first cache, she erupted into a virtual caching frenzy, making seven caches in seven minutes while Diamond remained thoroughly preoccupied with his digging. Finally, he again gave up, then came back to watch Slash, who abruptly stopped caching, instead flying round and round the aviary with a chunk of meat in her bill, as if suddenly not knowing where to put it. She finally cached it only when Diamond once again resumed trying to dig up her
initial
cache, the only cache he watched her make. This time, Diamond was finally successful in finding the meat. After eating it, he came to the bait pile
himself. When Slash was preoccupied in feeding there also, Diamond suddenly made four caches in three minutes. Afterwards, I chased both of them out of this portion of the aviary into the adjoining aviary in order to learn if they could recover their caches the next day.

On February 6, I allowed both birds back into the enclosure to find out who would recover which cache, and how fast. Although Slash had acted frenziedly the previous day while caching, she was calm and composed today. Nothing seemed to disturb her, not even me. She calmly went to one of her caches and ate the piece of meat retrieved from it. Then she flew to the next one, and so on.

Diamond, who had the day before made only four caches of his own, first went to where Slash had made three caches and probed briefly in the snow. He did not seem to know the precise locations and recovered no meat, although for Slash he was probing too close for comfort. She flew over. Diamond apparently knew Slash’s intent to punish his intended trespass, because he made a submissive display before she even got there. He had never made submissive displays to her before. Slash did not attack. Instead, she walked by him and simply reached down into the snow and pulled out her cached meat to hide it elsewhere.

The observation done, I opened the gate leading to the main aviary where the raven crowd was feeding on a food pile. Slash instantly flew in to join them at their feast, grabbed a piece of meat, and came right back into the part of the aviary from which I had just chased her! Although she was a wild-caught bird, she perched with her back to me. She held the food in her bill and all the time watched Diamond instead of me, probably waiting for an opportunity to cache when her competitor was not looking. Neither paid much attention to me. Their attentions were on each other and where to cache their food so that the other could not see them.

In another experiment on February 10, I observed recoveries of caches that Yellow O and Diamond had made the day before. Diamond had made thirty-three caches, and Yellow O only two. In one hour, Diamond recovered eight of his but made ten mistakes—six unsuccessful recoveries of his own caches, and four apparent recovery
attempts where there was no cache. Yellow O, in contrast, recovered both of his caches plus two more of Diamond’s, and made no mistakes. Although the birds probably were capable of recovering many more caches, they had no need because they were soon satiated, so I chased them out to continue the experiment the next day.

Later in the month, on February 27, Number 106 Blue and White Blank were tested for their ability to recover the caches they made two weeks ago. White Blank had made five caches, and today went to all five. Number 106, a new bird from the same group, had made thirteen and tried to recover only three. He dug for a full eight minutes at one site, before he got his piece of meat.

I later allowed four birds to cache simultaneously, removed them from the aviary, and let them back in one month later. Only two of these birds had cached, and these two walked continually all over the enclosure giving the impression of searching. Perhaps they knew the food was in this enclosure somewhere, but they didn’t seem to know exactly where. Meanwhile, the two birds who had done no caching at all sat quietly, hardly moving. They acted like birds in the control experiment.

The control consisted of forty food caches that I made in the birds’ absence (while they were out of sight in a side aviary). I marked the locations of those false caches in snow with branch sprigs and twigs. Then I let the birds in. None of the forty false caches was recovered by them. I recovered them all myself after one day.

My experiments were the first to prove that any bird could remember others’ cache locations, and my anecdotes consistently demonstrated that ravens also have counter-strategies that foil the considerable cache-parasitism capabilities of their fellows in a crowd. In experiments to test this three years later, in 1995, I provided Fuzz, Goliath, Houdi, and Lefty with piles of food when they were either all four together as a group, or when they were each provided food in isolation, one at a time. In the first situation, when I put down a pile of food chunks, all four instantly descended onto it, grabbed all they could, and started caching immediately. Their caching trips were short. Each bird
attempted to return immediately to the food pile to get another load of meat, as if to carry it away before the others might get it. Only the bird who eventually got the very last piece of meat from the pile invariably did not cache that piece immediately. Instead, it carried the last piece about, leisurely fed from it, and eventually cached what remained of it with great deliberation. Similarly, when only one bird at a time was given access to the same amount of meat, caching proceeded at a leisurely pace. The birds therefore appeared to monopolize as much of the temporarily available food as possible, and caching was their way of choice. If that was all, they should have cached closer to the source when they were in a crowd than when alone, to increase caching speed. Instead, with others present, they went farther to cache, going into the side aviaries where they could cache in private. The results made sense if the birds also attempt to take the uncached food away from others and to hide their caches from their sight.

Ravens’ caching behavior relies on their capacity to “track” objects. If they see a piece of food put into the snow, they “know” it is there and may dig six or more minutes for it. As soon as I or another bird removes it, they stop. Their minds seem to be like a chalkboard. They have the capacity to register many locations on it, but with each retrieval they “erase” that site from further consideration. I saw something even more sophisticated in one probe. In four different trials, I showed three of my ravens two halves of a cashew nut, and as they watched me from a perch, I buried the halves next to each other in a bare patch of snow. White twice found one of the nuts in less than a minute, then left. Orange showed faith that there was more to be had by continuing to dig after the one piece had been removed. The pieces of nuts were difficult to find in the loose, powdery snow, and in two trials he dug for 3:15 and 2:40 minutes, respectively, without finding them. In the third trial, Orange got one piece in 75 seconds, and both Orange and White continued to dig for another 2:50 minutes before giving up. At the fourth trial, Orange got a piece of nut in five seconds, then Red joined in and they both dug for 70 more seconds.

Although it may seem logical to suppose that the ravens have awareness of others’ actions because they anticipate others’ responses
before they occur, not everyone agrees with that conclusion. The alternative supposition is that the behaviors are stimulus-response phenomena in an infinitely complex chain of unconscious reflex responses to stimuli, ad infinitum. Most behaviorists would be convinced of awareness if, as has been shown with some primates, ravens lie. What is a lie? I would argue that pretending to make a cache and then actually hiding the food someplace else amounts to a lie.

In deception, a signaler behaves in such a way that a receiver registers something that is, in fact, not occurring. As a result, the signaler benefits and the receiver pays a cost. That is a behavioral ecologist’s definition. To a psychologist, however, lying is not only the giving of false information. Lying, from the psychological perspective, implies that the giver of information is aware of the fact that he is giving false information and that he knows this information will be interpreted by an intended receiver. I have evidence that ravens lie when I wear my hat as a behavioral ecologist. However, as I have indicated, I attempt to go beyond that perspective in this book.

I had on numerous occasions seen ravens make false caches—bury food and then immediately recover it to bury it elsewhere—i.e., they lied. However, I had not necessarily interpreted that as conscious lying. As an ecologist, it seemed simplest for me to assume that proximally the birds were only playing or being fussy about their cache sites, with no conscious deception involved. Making false caches can function to deceive, since false caches are sometimes checked by others; but as much as I believed the birds were aware in some ways, I did not think this behavior, by itself,
proved
awareness. Maybe they always act as if they are being watched without having any conscious knowledge of their actions. Maybe making a false cache is beneficial and costs little to do, and they evolved complex programming to do it unconsciously.

In a complex animal, the results of any one experiment almost always encompass several realities or perspectives. To see the proverbial “elephant” described by several blind men who touch it in different places, especially one as huge as consciousness, it must be examined simultaneously at many points, and from many perspectives.
The jury is still out, but nevertheless the details of the ravens’ behavior indicate to me that the birds predict and anticipate the behavior of their conspecifics. That may be as close to exhibiting consciousness as it gets. To react flexibly and in an anticipatory fashion to a wide
range
of actions (as opposed to a few specific ones) before they have occurred makes the hypothesis that the animal knows what it is doing increasingly more plausible, and the idea that all of their behavior is unconscious, unlikely.