As he sang, he raised his head high, often turning and gazing in all directions, alternately preening, stretching, picking at twigs, and gulping bills full of snow. I talked to him, telling him how beautiful his raven song was—that it was the most beautiful thing I’d ever heard. He didn’t know precisely what I said, but I venture he got my message; he would have responded differently if I had made sharp, rapid yells toward him. As I had intended, he showed me not the slightest visible attention. He continued to sing, rising to another loud, rasping crescendo, then fading into a series of soft chuckles and gurgling sounds. A second recent releasee was engaged in a similar monologue far down the hill in the nearby woods, where it was also all by itself. I had never once heard these raven songs where there was a large audience, at a carcass, for example.
An anthropomorphic biased view could be that the birds sang because they were overjoyed to be released from the cage. If it had been freedom, then they all should have started to sing when first let loose. They knew they were free, because they perched in the woods all around, then returned into the cage, onto it, and all around it before dispersing. None of the twenty-two had, to my knowledge, sung at all during the whole previous year while they were in the crowd. On another occasion, I released three birds out of four, and the bird remaining alone in the cage was the one that erupted in song. I concluded that they started to sing because the others were gone. As previously mentioned, dominant birds may totally silence others of their own sex.
Their expressions of anger are usually directed toward another raven and hence they are a potentially far more immediately useful signal than expressions of joy for self. The raven’s anger is expressed most palpably in those individuals that know their enemies and are brave and knowledgeable enough to defend the nest. When a human or presumably other predators approaches their nest, these birds violently hammer branches, tear off and toss twigs and cones, and give deep, long rasping caws that convey that the caller is powerful and serious. A raccoon trying to raid the nest would read this display correctly, and a human may do so as well.
One out of a myriad of other examples of ravens expressing anger occurred in the aviary complex where the wild-caught birds had become thoroughly used to my bringing them food. When I set food down, they always flew right over and started feeding. One day, I happened to be blocking the door to the side aviary with C48 inside, who wanted to get out by me to get to the food. He came up to me, looked me in the eye, and erupted in the same long, deep rasping alarm or anger calls that greet me when I intrude at nests with young. This demonstration would have been unthinkable earlier in the year, when he was still fearful of me and always yielded. Fright always won out over all other considerations. This time, he did not fear me and he dared to show his emotions. Given the circumstances, his message was clear to me: “Get out of the way—I want to get past you to the food.” Without the context and my personal experiences with ravens, his vocalizations would have been meaningless. They would have contained no message.
He would not have given his message if he did not feel he had a chance of making me yield. He had in effect talked with me, because his message was directed at me only. I heard, understood, and stepped aside. He immediately slipped by.
Alert and confident.
Body language is also extremely important to ravens. Obviously, actions speak louder than words with them. Contrary to numerous accounts in the literature, I have never heard a raven give an alarm call when I have come near a feeding crowd. If only one bird of the group sees me and flies up in alarm, the others also fly up almost instantaneously. I have on several occasions been hidden from the feeding crowd when a bird that is flying overhead sees me and changes the rhythm of its wing-beats, usually in rapid backpedaling of its wings. Without one vocalization being given, the crowd instantly flies up and scatters, even though they may have been feeding out of my view over the rise of a hill.
Since ravens are much smarter than insects, they don’t need a long song and dance, as do honeybees, to alert them when one of their fellows has found food. Information is contained in simple action. Suppose a group of four to five ravens who know where there is food eagerly leave the roost thirty minutes before sunrise. Since all the birds who know where food is go first of all to feed in the early morning, these birds may realize that something is up when others leave so eagerly and so early. Not knowing where food is, the hungry birds follow those who demonstrate strong motivation.
My speculation is not without data. I spent one winter getting up every day hours before dawn to climb tall spruce trees near baits I had put out. Aside from the pure enjoyment of climbing snowy trees in the dark at subzero temperatures, I did it to count birds. I found that the first big crowds at a carcass always arrived before light. On succeeding days the birds came increasingly later and in smaller groups, even as individuals and pairs. Once feeding had begun, birds knew where the food was. From then on, they did not have to follow any other bird, and they did not have to leave the roost long before dawn when the first birds left. They were free to come on their own at any time. Some would say the ravens were not conveying information, and that this was information-parasitism instead. That implies that one benefited at the expense of the other. In the case of the ravens described above, both followed and follower birds benefited; they both got to feed by overcoming territorial defenders and/or reducing their fear of the food. So it was a communication, even if nonvocal.
Seventeen of the Most Common Vocalizations
of Fuzz, Goliath, Houdi, and Whitefeather
1 = loud, hollow-sounding carks that were given singly or widely spaced in time
2 = soft mm-sounding intimate calls
3 = low honks
4 = nasal honks
5 = rapidly repeated caulk-sounding calls
6 = very rapidly repeated rap-rap-rap calls
7 = deep, short rasping calls
8 = long, undulating territorial advertisement calls
9 = long, deep, loud rasping calls
10 = loud begging yells
11 = knocking calls, like stick in a bicycle wheel
12 = oo-oo-sounding calls
13 = dog whine-like calls
14 = cheow-sounding calls
15 = soft upward inflected calls given singly
16 = whine-thunks
17 = continuous sing-song monologues
Typical male macho display, showing “ears,” elevated head, spread shoulders, and puffed-out throat feathers.
SEVENTEEN
Prestige Among Ravens
WHEN ANY GROUP OF JUVENILE ravens is put together in an aviary for the first time, they immediately challenge each other, and they soon sort themselves out into a dominance hierarchy. Notwithstanding the dominance switch between Fuzz and Goliath, and later Red and Yellow, changes of status are rare. In general, a low-status bird may improve its status only by leaving its associates and joining another group. The reverse, resulting in a loss of status, can happen as well, as the following incident indicates.
A raven crowd had slept in the thick fir grove a hundred yards from calf carcasses, but only ten birds came to feed at them on March 1, 1993. One was a new bird I had never seen before, with a long, curved upper bill that projected about a half inch in front and then curled down. “Hawkbill” contrasted with others that had appeared on occasion, including “No Bill” (half of upper mandible missing), “Peg Leg,” “One Eye,” and “Crump Leg,” and still others who may have been victims of gunshots or traps. Hawkbill, being new among this crowd, was confident, launching into a knocking call duel with another female.
Female raven in power display, making knocking calls.
Suddenly, a violent chase ensued through the forest surrounding the carcass. The chaser had singled out a specific bird with whom it stayed relentlessly, weaving in and out among the trees and past all the other birds. I suspect the chased one was Hawkbill, because she was then missing from the feeding crowd. When she returned only twenty minutes l
ater, she stayed at the periphery of the crowd, where she was ignored. I watched the feeding crowd for another half hour. Throughout this time, she stayed well out of the others’ way, maintaining a submissive posture. She had changed from an apparently dominant bird when she first arrived to one who always yielded to the others. Since the chase, she had not made a single knock.
In the male peacock and most other male birds, the showy and self-aggrandizing behaviors are under the control of hormones, principally testosterone. To maintain high output of testosterone, the testes increase some thirty times in size. In ravens, high-status birds suppress the sexual development of others of their sex, not just their behavior. I wondered if the dominants’ brains might be testosterone-soaked at an early age. To find out, Michael Romero, an endocrinologist now at Tufts University, and I collaborated in making a probe into raven’s blood hormone profiles.
After only one winter and innumerable imaginable and unimaginable mishaps later, I managed to get sufficient blood samples from ravens of known status. I sent the raven blood, and for fun and curiosity a sample I had taken from myself, to Romero, then at the University of Seattle, for the hormone assays. The results were exciting, because I had not anticipated them. The blood samples had been taken in late winter, the breeding season for birds (although ours were not breeding). I had sampled adult (black-mouthed) and juvenile (pink-mouthed) birds of both sexes and of both high and low status. Testosterone levels were low, and we detected no statistically significant difference in testosterone levels in the blood between the birds’ status and sex. The big dominant black-mouthed males had only slightly greater testosterone level than the pink-mouthed immature females. Testosterone is therefore not the hormone involved in maintaining status in ravens. Nor can it be involved in achieving status, because ravens sort out relative status within minutes after they meet and size each other up. Unfortunately, reviewers of our manuscript felt our results would “confuse” the current ideas rather than support them, so it was not accepted. I, on the other hand, felt that if they had supported them, they would not have been newsworthy.
We had also assayed corticosterone levels. Corticosterone is a hormone that is released into the bloodstream with increased stress. Unlike testosterone, this hormone can be released quickly, in minutes. We sampled within a minute of capture and later, and found, as expected, a quick rise in blood corticosterone levels after the birds were captured, then this hormone again as quickly declined to basal levels. There were no differences either in basal or rise in stress hormone levels between the birds at the bottom or the top of the pecking order. I was pleased to see the birds’ physiological stress response decline so quickly, and also to learn that low-status birds did not seem to be more stressed than high-status birds.
Dominance in ravens is not maintained by hormones, but by body size. In birds, real size is not easily apparent, because they are enclosed in a thick layer of feathers. The feathers may be fluffed out or depressed, making a bird seem any of a number of sizes. During the initial greeting ceremonies of males, the newcomer to a group often flaunts his size, walking slowly and deliberately, strutting with his head held in a grand, self-assertive manner accentuated by gestures. The head is held high with the bill angled up, which adds considerably to the birds’ stature. The elevated “ears,” partially puffed-out head feathers, and greatly broadened neck with extended throat hackles enhance his apparent bulk. The throat hackles glisten from reflected light and vibrate from swallowing motions, thus drawing attention to the neck, which seems inflated to nearly the thickness of the body. Bulk at the lower end of the body is accentuated by covering up the skinny stick-like legs with long, hanging belly feathers that cover the legs like trousers. Approaching a possible rival, the male may forcefully snap his bill and also flash his strikingly white nictitating eye membranes like headlights turning on and off. He walks, as one raven-watcher quipped, “with an air of cockiness that makes him resemble a street tough hogging a sidewalk.”
A subordinate bird—here in process of blinking, as the white nictitating membrane is sliding across the eyeball, forward to back.
If the bird that is approached is smaller and is suitably impressed by all this show, it backs down by pulling its head tight into its shoulders and pointing its bill down. That usually settles the encounter. In contrast, if a more confident bird is approached, it may rise to the challenge with a similar self-aggrandizing display. If both are suitably puffed up, a physical contest may ensue where the two antagonists grapple and fight. Full use of the bill, a potentially lethal and powerful weapon, is seldom instigated. The contest is lost by the bird who is first to show subordinate gestures.
Do smaller birds “cheat,” and try to bluff larger birds? The answer is, not much. Any individual who puts on a show is sure to be challenged by others who consider themselves a notch or two above. A prestige display (as could potentially be stimulated by testosterone) in a weaker bird can be costly, because it will be challenged. A status display in ravens is thus generally an “honest” advertisement of size and power. It is not a testosterone puff, and cannot be one.
One of the elegances of raven behavior, as I’ve mentioned, is that the birds reveal something else entirely besides their confidence and rank and prestige when they first meet and size each other up. They simultaneously reveal their sex. That is, there are two prestige displays, one for males and one for females. As a result, since male and female ravens have to our eyes identical physical appearances, only those ravens who have high rank are allowed to reveal their sexual identity. As shown in the following example, the chronically low-ranking birds remain effectively genderless.
In April 1992, I had a group of wild-caught birds in the aviary that included White Slash, a female (so name for a wing mark designation), and Blue Diamond, a male. They perched together, preened each other, and the female always begged from him. They were the only solidly mated pair of the group, and they never offered their preening favors to any other bird. Blank White, another female, was loosely “going with” No Tag, who had previously preened with several others. Yellow 0, as named earlier, a big juvenile male, preened Green once, and she preened him back. Otherwise, he made no displays to any birds, nor did any females sidle up to him. He seemed genderless and anonymous. That changed in minutes after a little mix-up.
I tried to chase some birds out of the side aviary and into the main aviary for an experiment on caching behavior (see Chapter 22). During this transfer, Yellow 0, the silent unassuming male, was left behind alone with a female, One Dot. It wasn’t planned. They simply didn’t make it out in the rush. To avoid causing more disturbance than necessary, I left them there. Once they were alone, they put on quite a show. I had never seen anything like it from those two before, when they were with the others. Both were juveniles with bright pink mouths who had not yet molted into their glossy feathers, yet from their behavior now it might have been easy to presume they were fully adult. The two perched side by side. He stood tall and erect with his bill up in the air, his throat hackles puffed out, his flank feathers and wings spread broadly to the side, making himself look big. He erected the feathers on his head. At times, he also erected his “ears” in the typical fashion of a dominant male. He flashed the white nictitating membranes of his eyes at her, and went through the male vocal repertoire of choke sounds, gurgles, bill-snaps, grunts, honks, and quorks of high and low pitch. He gave inflected, deep, and nasal quorks, deep rasping quorks, and hollow gong sounds. Apparently impressed, One Dot bowed with fuzzy head and made the typical female knocking sounds. Since the sexual displays look virtually indistinguishable from the social display of dominance, I now understand why they did not perform them in the company of the crowd; Blue Diamond and others would have instantly attacked to squelch them. Here, both could strut their stuff without interference.
If the largest birds can more easily display to defend food, secure mates, rear offspring, and keep warm at very low temperatures (because large body size aids in co
nserving body heat), why isn’t there runaway selection for ever larger body size? In ravens, as in all others, everything has a cost. Like a male peacock’s tail, a male raven’s dominance is at times highly beneficial, but most of the time it probably has negative value. The energy cost of achieving and maintaining a large body mass may not always be obvious, because at large carcasses where ravens feed, food is unlimited, even to large dominant birds.
Perhaps when the food resources that support large size and dominance are removed, then the potential payoff is gone and the smaller subordinates “win.” That there is a cost to the raven’s dominance as achieved through size was suggested during an unplanned experiment. I had left a group of fifteen captive ravens and one crow to be cared for by a responsible neighbor-friend when I had to leave for three weeks. To make it easier for Ron, my helper, I procured five calf carcasses, dragged them up the hill, and put them in cold storage in a pit in the ground. I covered the pit with an insulating layer of last fall’s maple leaves to make sure the meat would last. I also left several bags of potatoes that could be boiled and fed to the birds. I had explained the necessity of cutting the calves open to expose the meat, and I left a sharp knife for the task. The welfare of the birds assured, I left feeling that all was in order.
Mind of the Raven: Investigations and Adventures With Wolf-Birds Page 24
