Mind of the Raven: Investigations and Adventures With Wolf-Birds

by Bernd Heinrich

  We have no clue who the apparently very rare “helpers” at raven nests might be. They could be neighbors defending their nearby nests, grown offspring that have not dispersed, strange males seeking friendship for eventual extra-pair copulations, and/or neighbors who have joined in a coalition for mutual defense.

  Carsten Hinnerichs at the University of Potsdam in Germany told me that late one winter, at a time when ravens get ready to breed, he saw six ravens at different occasions over two weeks regularly flying together as a group of three pairs. The pairs had fuzzy head feathers, made glug-glug-glug calls, and acted like typically courting birds. Although juveniles gambol in crowds throughout the year, nobody had ever before reported seeing ravens engage in mating displays as a group—only as isolated pairs.

  The six ravens that Carsten saw as an apparent group of pairs at nesting time were an anomaly that excited me greatly, because it could shed light on the flexibility of social arrangements. Carsten found three fresh raven nests in “a little colony” in the pines nearby at the edge of a big dump. By April, each of three nests held an incubating bird. The spacing of the raven nests so close together that they were virtually a small colony seemed extraordinary. Here was concrete evidence for an amazing shift in territorial behavior from that which Grünkorn had documented in northern Germany (Chapter 7) and from what I had been used to seeing in ravens in New England. These nesting birds, like some others on an oceanic island (Noglaes, 1996), apparently were tolerant of each other. In Maine, even a small food item such as a dead snowshoe hare is fiercely defended, and other ravens coming into the vicinity are aggressively chased for miles. A larger food item such as a calf or a deer carcass is also fiercely defended; but, at least in the aviary, after the bird’s bellies are full, their intolerance toward at least familiar individuals almost vanishes. The German ravens’ extraordinary tolerance might not be so unusual at all. Perhaps it was a common response to a rare situation.

  The place, the Zehlendorf dump, was a raven’s Shangri-la. There was no end to good food, and it came reliably and without end, delivered by dump trucks day in and day out, all year from one year to the next. Perhaps this steady food supply was sufficient to enable communal nesting. But then all three nests that had eggs ultimately failed. Carsten found eggshells strewn on the ground below the nests, as well as torn-out nest lining. A study by Lo Liu-Chih from Taiwan, at the University of Saarbrücken in Germany, provides one hint of what might have gone wrong.

  Liu-Chih’s detailed analysis of many hundreds of raven nests compared nest success in different ecological sites in Germany. One of these sites was at the Rostocker heath, and another was in the area around the Grevesmühler dump. Like Carsten, Lo found a virtual colony of ravens in the pine forest within one hundred meters around the dump. Surprisingly, despite the large food supply, nesting success at the dump was much poorer than in the wild heath area. Birds started later, many nests were not finished, and three-quarters of all nesting attempts failed altogether. The “successful” nests averaged only three young, as opposed to five, typical in the nearby areas. What was even more strange, the young had thin thigh muscles, characteristic of birds that had received inadequate amounts of food. Lo thought that although food was more plentifully available at the dump, the adults living there had to spend so much time defending their nests, they had less time to forage.

  But defending the nests from whom? Was there really strife among the closely nesting pairs? It seemed to me that an equally plausible hypothesis was one diametrically opposed—that the pairs cooperated. Perhaps they even defended “their” dump and their nests from the hordes of nonbreeding juveniles that are invariably present at all dumps. Near the time of the three nest failures seen by Carsten, there had been a sudden influx of about fifty ravens that took up residence at the dump. Eventually, in mid-May, the crowd had swelled to nearly five hundred. Perhaps it was they who destroyed the nests. Perhaps the decreased nesting success of pairs at the large food bonanzas that Lo and Carsten had described was not so much an indication of strife among the pairs as conflict with the ever-present nonbreeders. To try to find clues, I asked Carsten to show me the Zehlendorf dump, and my visit there in July 1997 was the highlight to my visit to Germany.

  Playing detective, I sensed two strange things. First, the coincidence of the nest failures with the arrival of hundreds of juvenile vagrants; and second, the extraordinarily close placements of the nests right next to the dump, with the much more distant placement of the vagrant’s sleeping roosts. I paced off the distance between the three nests next to the dump (100 to 160 paces), and closely examined the ground under each nest. In Maine, I had on four occasions (years) seen the ground littered with nest lining after a crowd of juvenile vagrants had been in the area. In spring 1998 in Vermont, when I had a large feeding crowd by the house, both local raven nests failed for the first time. As in New England, the ground under each nest at this dump was littered in all directions with tufts of nest lining. Normally, nest predators take only the nest contents. No animal other than another raven would so systematically engage in such strange behavior as tossing tufts of nest lining all around. Here was more circumstantial evidence that the strife was not among the pairs, but between the nonbreeding vagrants and resident breeders.

  When I visited the Zehlendorf dump, there were still about five hundred ravens there. Opposite the pine trees on the other side of the permanently stocked feeding place, dump trucks roared in and the wind swept up a large mound of sand on top of which crowds of presumably well-fed juvenile unmated bachelor ravens gathered to play in the wind. As we watched the large queues of ravens on the crest of the sand bar, one after another would spread its wings, be lifted up, fold its wings, and be gently let down again, riding the air waves like surfers on a beach. Many others used the high thermals instead. They came flying in from miles away. With raucous cries, they circled, dove, and tumbled among the cumulus clouds. At night they gathered in a noisy raucous throng about a mile into the pine forest from the edge of the dump in a communal roost where the ground for over an acre was littered with feathers, pellets, and mutes.

  Something still didn’t add up. Why did five hundred ravens fly as much as a mile to roost at night, when they could have roosted directly at the dump itself? Why instead did the multiple pairs always nest directly at the dump, when they could have nested isolated from each other and this crowd, ten or more miles away from all the bustle? Why did the nests fail in one case in the egg stage already? I suspected there was a reason for the proximity of the nests to each other and their location directly at the dump. As my aviary experiments had shown, ravens’ tolerance for one another increases markedly both as a function of amount of food they have available and the length of time of their mutual association. It was almost certain that the three neighboring pairs nesting at the Zehlendorf dump knew each other, opening up the possibility of a mutual alliance.

  Vagrants are very often successful in overpowering pairs. Why not vice versa? Why could neighboring pairs not team up when they no longer need to compete for food? By sharing the dump, the two to three pairs would still have more food than needed, but it could make a huge difference to their nesting success if they could repel vagrants that destroy nests. As this book was going to press, Carsten informed me that the small colony of three raven pairs at the dump had now increased to nine! Had more been allowed to join the club, as more individuals had gradually gotten to know each other due to their continuous association at the permanent food.

  More food means less competition and less aggression (or more, depending on circumstances), whereas less food provides more competition and leads to more aggression. A small or medium-sized carcass is worth defending, and in the forests of Maine, neighboring pairs meeting at a rabbit carcass are induced to fight over it. Fighting would destroy mutual trusts and sharing. Yet sharing would be mutually beneficial at a large “permanent” food pile such as a moose carcass, because meat shared by one pair with another would have a mi
nor immediate negative impact on the sharers, but a major positive immediate impact on the recipients. If the recipients were to act in the same way at a future carcass, then all would benefit in the long run. Ravens may live for decades (Clapp et al., 1983), and they nest at the same site year after year. I wondered, therefore, if or how neighboring pairs might get to know each other, so that sharing at a future potential moose carcass could be possible for mutual benefits? Might it be in such aerial play as I had commonly seen among adjacently living pairs, which reminds me of interdepartmental touch football?

  Raven hanging by its bill from a long, thin, flexible branch (left), and hanging by feet from rope (right).

  TWENTY-FOUR

  Play by Ravens

  PLAY IS NOTORIOUSLY DIFFICULT TO define. We can all recognize it at the extremes, but we cannot fit it into an exclusive category of behavior. According to most definitions, it is behavior that is seemingly purposeless, but behavior may seem purposeless simply because the observer hasn’t figured out what the benefit is. Benefits could be long-delayed and have many repercussions, not just one. For example, play fighting may function to develop skills for later use, establish important social relationships with peers, and build muscle tone and coordination needed to escape predators. However one may define play, young animals are not likely motivated to perform play for the rewards they ultimately may get from it. Play is often nonstop action with bizarre twists that has its own phychic reward, like hanging upside down by the feet. I have not attempted to organize my observations into such categories as “object manipulation,” “social play,” or “play fighting.” Rather, in the following I report activities as they occurred, in specific snippets of time.

  On November 11, 1993, I saw Lefty dangling upside down from a thin branch of the pine tree in the aviary with her head held horizontally. Within a few seconds, she let go with both feet, turned in the air, and landed right side up on a branch below her. She regained her previous perch, flipped over backwards to hang again, then let go and flew off.

  With time, she incorporated more variety into this oft-repeated stunt. Two weeks later, she hung with only one foot, grasping a piece of bark in the other. She repeated her upside-down hanging maneuver three times in about two minutes, always holding the same piece of bark either in the bill or a foot. At last she landed on the ground, where she picked up a bark chip and stuck it into a hollow plastic tube. She lifted the tube at one end till the bark slid out the other end. She repeated this maneuver three times. After she dropped the bark chip, she scraped freshly fallen snow off twigs with her bill. Within fifteen minutes, she picked up another bark chip, picking at it, carrying it, and at last caching it under a log. Goliath, seeing her hide something, came and dug in the ground nearby. So did Fuzz, but neither bird found anything of interest. Then Lefty chased Houdi, stopping often to wipe her bill on branches and singing a gurgling-gargling song with head fuzzed out and throat hackles puffed out. Lefty then resumed chasing Houdi.

  In early December, I again saw Lefty hanging upside down. She was dangling from a very thin and flexible branch with her right foot while her left foot held a wood knot. While still hanging upside down, she passed the knot back and forth between her bill and the free foot. Sometimes with the knot in her bill, she hung with both feet. She flew up to the same branch three or four times in succession with the knot in her bill, then transferred it to the other foot before flipping over. Meanwhile, Houdi, Goliath, and Fuzz were dragging sticks on the ground and didn’t seem to pay her any attention. For a few seconds, Houdi fluttered from a swaying perch, hanging with her bill only. Within the next half hour, Houdi had twice more tried to dangle by her bill from the same branch, whereas Lefty hung upside down by one foot, holding a small rock in the other. She picked up a pebble, and while holding it in her bill, turned over frontwards on another twig, continuing to manipulate the pebble in her bill. The pebble eventually fell or was let go. Then she let go with her feet to fall and then fly.

  Two days later, I saw Houdi pick up a foot-long thin twig and carry it all over the aviary, occasionally stopping, holding it with her feet, pecking at the ends. After five minutes, she dropped this stick and snapped another off the pine tree in the aviary. This twig was two feet long. Fuzz tried to take it away from her right away, and Houdi gave it up without any resistance, then walked over to a calf carcass to feed. Lefty then picked up Houdi’s first stick but dropped it in less than thirty seconds. Fuzz, too, dropped his long stick.

  All birds were then without sticks. Goliath snapped off another long branch, and Houdi came over and pecked at the exposed stub where the branch had snapped off. Fuzz and Lefty meanwhile had a tug-of-war with a gray squirrel skin. Goliath had broken the stick off, then Houdi got it because Goliath dropped it. He then pecked at the place where the branch had snapped off, where Houdi had pecked before him. Goliath joined Fuzz and Lefty at the squirrel skin; the latter then both departed and Goliath quickly lost interest. Lefty resumed picking on the squirrel hide, while Houdi joined her. Lefty flew up onto a long perch that somehow loosened and fell down. All birds became frightened and flew into their sleeping shed, where they stayed for a minute. After venturing out, they refused to go near the fallen stick, and only after one hour and thirty-six minutes did they come down to the ground. I gave them a new toy, an aluminum can. Within seconds, they approached it, just gently touching it with their bills and then doing jumping jacks. Soon they jabbed it vigorously—all except Lefty, who showed no interest. The can was soon torn apart. Houdi ended up with the bottom part, and Fuzz had the top part. Both parts were shredded ever finer.

  Four months later, when I gave them another beer can, Goliath got it first and hammered it for five minutes before losing interest and dropping it. Houdi grabbed it, but Lefty gave chase. For about one hour Houdi, with beer can in bill, was chased at intervals about the aviary. Finally, she dropped it. Did Lefty then swoop down to grab it? No! She let it lie. So did the others. Houdi went on to hang upside down with her right foot, while gurgling her raven song. Goliath rolled on his back on the ground, holding a branch up in his feet.

  Lefty hung by both feet, then by only the right foot. After looking all around, she smoothly turned back up to the branch by going forward, assisted with wing-beats. She made her head fuzzy and called hoarsely, then did the same sequence again, this time dangling by one leg before letting go and dropping, after pecking the branch she had perched on.

  One day in May, at the age of one year, Houdi repeatedly peered into an eleven-inch-long, square, brown plastic tube. After peering into one end, she picked up a green tennis ball, another long-neglected toy, and stuffed it down into the hole. It fit snugly, and she pounded it in by hammering it with her bill. When I looked into the aviary the next day, the ball was loose. Houdi retrieved it and again shoved it into the hole, stuffing dead leaves behind it. She then pulled the leaves and ball out, and repeated the process twice more. Fuzz began to take interest, pulling the leaves and ball out, pounding the ball back in, shoving debris behind it, pulling all out, and repeating the process twice. At first, Fuzz had some trouble getting the round ball to fit into the snug, square hole. He braced the tube with his foot to hold it fast while he pounded the ball in. When he was finished, Houdi came back and inspected what he had done. Fuzz came back and inspected also, putting more leaves behind the ball. Then he pulled it all out again, pounded the ball in deeper with his bill, then pulled it back out and pushed it into the other end of the tube, again stuffing leaves behind it. In the afternoon, Fuzz took the ball out of the tube and hid it under leaves nearby. By then, I had become satisfied that they were not afraid of this new object, the tube, and that they had learned it was hollow. Perhaps they had been productive. I then did tests to find out if they could put their knowledge of the nature of the tube to use, to see if they might keep track of objects within it that they could no longer see with their eyes.

  Their antics were always fresh, unpredictable, lively, and constant. Nothing
seemed to stop them, even when at the end of January temperatures dipped to minus 45 degrees Fahrenheit. In the morning, they were almost white-headed. Moisture from their warm, exhaled breaths instantly turned to ice crystals and condensed onto their fluffed-out head feathers. The birds started attacking a plastic milk container that had already received a thorough pounding the day before. Their only visible concession to the cold were their belly-feathers, fluffed out so that they reached down to their toes when they stopped to perch.

  They often played “catch-the-stick,” but the most popular activity going was snow-bathing. In its simplest form, this involved skooching down and flapping their wings, just like bathing in water. But there was more. They also slid forward on their breast and belly feathers, being assisted not only by wing-flapping and leg-flailing, but also by gravity. Houdi twice rolled completely around sideways down a short bank of snow. Goliath, Fuzz, and Lefty did only partial rolls. As always, these ten-month-old birds were vocal throughout, making nearly constant soft utterances. They pushed themselves forward in the snow on their bellies and went through all the motions used for bathing, especially after a new fluffy snow had fallen; but snow play was not restricted to fresh snow. There had been snow on the ground for well over six weeks by Christmas 1995, and on the evening of December 24, I gave Fuzz and Houdi a “present”—I made a two-foot-high snow pile in their aviary. As I had anticipated and hoped, both birds appeared to enjoy their new toy the next day. They perched on it and pulled out several loose sticks that had gotten packed in. Houdi slid down and turned one complete roll. She repeated the maneuver six consecutive times. Fuzz didn’t try it, although he was by Houdi’s side almost continually.