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

by Bernd Heinrich

  The ravens’ preoccupation with little round objects presented a less trivial problem when those objects were the eggs of the endangered least tern in California. A group of researchers (Michael L. Avery, Mark A. Pavelka, David L. Berman, David G. Decker, C. Edward Knittle, and George M. Linz) tried to solve this problem with negative conditioning. They set out Japanese quail eggs, which resemble tern eggs, treated with methocarp, a nonlethal chemical that makes birds ill. The ravens, not to be outsmarted, soon learned to distinguish between treated quail eggs and untreated tern eggs, and continued to eat tern eggs. Not to be outsmarted again, the researchers refined their tactics. They placed the methocarp-treated quail eggs at the tern colony several weeks before the terns nested. It worked—the territorial ravens soon learned that “all” the eggs at that site made them ill. When the terns finally laid their eggs, they had a brief respite. The resident ravens, who otherwise would have been shot, had now become an ally in conservation. By chasing away naive and as yet uneducated vagrant ravens who would have eaten the tern eggs, they inadvertently protected the tern colony.

  The ravens’ behavior rings true to us because we can see so many resemblances to our own behavior. My son Eliot at about one year in age behaved almost identically to the several-month-old ravens. He was strongly attracted to all objects that were new to him—spoons, cans, lids, an egg beater, film vials, bottles, a metal box, a knife. He would examine all items, if given a chance. All would soon be tossed aside, then ignored. The difference between Eliot’s and the ravens’ behavior is that the birds are only in this stage for a month or two, whereas the human baby’s behavior may continue for several years. Parents soon find that their living rooms, halls, garages, barns, and yards become littered with ever larger piles of obsolete plastic junk.

  Ravens’ curiosity declines with age. By the time they are four months old, they are already becoming shy of most novel stimuli. As they mature, that initial attraction to novel things reverses. They become increasingly fearful of novel objects. I once tested a crowd of wild-caught juveniles with all kinds of objects that my young birds found irresistibly fascinating—film canisters, bottles, cans, silverware, and the like. They ignored the items until they got really hungry. The older birds reminded me of my father. He saw a peanut butter and jelly sandwich for the first time when he was fifty-five years old. It may have amused him, but he would not eat one then, or ever. He “knew” butter doesn’t come out of peanuts, unless it was very inferior butter, and that was that.

  Two pictures of a raven cliff nest in Vermont with young about a week and two weeks old. Note feces (white) in raven’s bill due to nest hygiene, and the iridescent plumage.

  SIX

  The Fate of Young Ravens

  BLACKJACK WAS A MARKED WILD raven, Number 21, who fledged from a nest by the lake a few miles from my cabin. He was still in his clumsy postnestling stage when he examined a hamburger grill at the Mount Blue State Park beach. His left leg slipped through the metal grill. Perhaps startled, he jumped sideways. The metal didn’t yield but his young leg bone did, and he later lost that leg. Blackjack recovered and did fine minus one leg. By late August, he was still a picnic-junkie, and an entertaining one. Once, while rummaging inside a lady’s picnic basket near the same beach, he received another fright when the owner returned to reach into her basket, although she had a comparable shock, judging from her screams.

  Blackjack was fairly tame in early August, but became shy of people by early September. David Lidstone, a friend and volunteer raven watcher, kept track of him and other marked raven youngsters with a spotting scope. David continued to put food out at his campsite, and that was taken primarily by the young ravens whom David had helped John Marzluff and me tag at the local nests. Early one morning, when Blackjack made an appearance at the accustomed food source, he was viciously attacked by three current-year young from the nest just at the other side of the lake. The dispute could have been over the daily food bonanza, or perhaps Blackjack was a target because he was at a disadvantage with only one leg. The wild young ravens never attacked Jack, a vigorous young tame raven at my cabin. Nor did he attack any of them, although he once waddled up behind a Hills Pond nest youngster and pulled its tail. Soon after his scuffle with the neighbors, Blackjack was gone.

  Young raven with a little fuzz still on top of its head.

  I have often wondered what happens to young ravens after they leave their parents and their home area. Where do they go? Do they ever come back? What are their chances of survival? We have little more to go on than statistics derived from studies of marked birds in Europe, and they paint a bleak picture. Typically, only half survive their first year. These juveniles constitute a “floater” population without a fixed home. They are largely expendable as far as the nesting population is concerned, because they cannot breed unless a resident with a territory dies, thereby opening up a breeding slot. Adults can remain in residence for decades, and unmated floaters as old as seven years have been documented.

  Resident ravens in New England start to defend their nest territory in late fall. By mid-February, in the middle of winter, they begin building their huge stick nests lined with fur and shredded bark on some crag or conifer, generally a pine tree. The female raven, like other corvid females, lays a clutch of four to seven heavily speckled, greenish-blue eggs that she incubates for twenty-one days. At birth, the young are pink, blind, and naked, possessing only a few loose tufts of down feathers and weighing only about 25 grams. They cannot yet regulate their body temperature and are continually brooded by the female as they grow rapidly on the food that the male brings. In eight days, they have increased their body weight by about twelve times. In six weeks, they have reached the adult weight of 1,100 to 1,500 grams, when they leave the nest and begin to follow their parents, staying with them for the next six to eight weeks as they learn to forage. For the young birds in my aviaries, the prospects for survival during the first year would be much better than the odds they would face in the wild; I presumed all of my birds would live, with my care and protection.

  Normally, the young begin to wander away from their home area in late summer and fall. That’s when the heavy mortality begins. Since I wanted to keep Goliath and his cohorts, I needed to confine them in an aviary. When the proper time came, I hoped they would nest inside and become residents there. Then I would let them fly free because I hoped they would stay bound to their adopted home, having skipped the dangerous wandering stage when most deaths are likely to occur.

  Most of the 463 ravens we have captured temporarily and tagged at feeding aggregations at my study site in Maine have dispersed. We have seen few of them return. We had hoped that by marking them, we would be able to identify all the ravens we would see for many years, and we would thus have the basis for studying their social interactions. It did not turn out as we had hoped. On the contrary, if a large food bonanza attracts one hundred ravens, it is unlikely to contain more than one or two tagged birds, and these are usually adults from local nests. Most of the others, who are unmarked, must be from somewhere else. What has happened to all the birds with white, yellow, red, blue, or green patches on their shoulders? Where have they gone?

  Occasionally, someone may see a tagged raven. Very rarely, the person may even hear of the study and report back to me. The range of the eight nonlocal (beyond fifty miles) reports I have received was south to Boston, north to New Brunswick, Canada, east to Nova Scotia, and west to western New York State. The total area covered by these eight sightings is over two hundred thousand square miles. It is a wonder that I have received even one report from such a vast area, which, judging from the few returns, must be a minimum area. The main conclusion that can be drawn from the effort of capture-mark-release work is that in northeastern America, the birds do indeed travel very extensively.

  Map showing the recoveries and sightings of 12 of our 463 ravens that were marked in Weld, Maine. (The four dots near Weld represent resident adults that were frequently observed a
t the same site; all of the others are single recoveries or sightings.)

  There is nothing absolute or specific about these distances. In some areas, the birds presumably travel much more; in others, much less. How far birds travel is driven by the search for food. The more sparsely food is distributed, the farther the birds must fly to find it. But do they travel in sibling groups, alone, or with friends? A set of explicit observations at the time that the young become independent could yield insights.

  When I found myself with three recent college graduate volunteers eager to do raven work, and nine radio transmitters, the project was on. The question that seemed feasible and relevant was simply to ask if and/or how much the several young of any one nest stay together and/or intermingle with the young of other nearby nests. Do the young aggregate or overlap in their foraging ranges? To answer these questions, we would have to monitor at least two sets of young during the summer.

  I chose my first nest from the white pine grove at the edge of Weld village. This was a pair Marzluff and I had years earlier captured and which had raised young in our aviary. The next-nearest nest was located about a mile and a half from the first. Both nests were in tall, straight, white pines that were limbless for twenty to thirty feet, then had dead, brittle limbs most of the way up to the thick live branches in the crown where the nests were located. As always, it was a white-knuckle experience for me to reach the nests.

  The young at the first nest peered down at me over the edge when I got close. They were ready to fledge. And fledge they did the moment I reached the nest edge. I managed to grab two of the five young and put them into my knapsack to take them down to the ground, where I could attach the radios. The other three young landed a bit lower in nearby pine trees on their maiden flights. After descending to the ground and attaching a radio onto the large tail feathers of the first two birds, I climbed up after the others. Again, they flew off when I got near them. With each clumsy flight, they landed lower, and eventually they reached the ground, where I caught them. The process was repeated almost exactly at the second nest, except that this nest held only three young. We used up all but one of our radios. I was jubilant, though exhausted. It had been a great day.

  During the next week, I monitored the young by checking on their radio locations, and walked into the woods to locate them visually. On May 31, the members of both groups were perched close together on low branches. They were still within two hundred feet of their nests, but they flew off as I came within fifty feet of them. Three days later, the young were no longer near the ground, but instead perched high in the pine trees, now within a quarter mile of their nests. All eight radio transmitters were working, the birds were healthy and flight-capable, and the experiment was in place. As I left on a long trip, I felt confident that my very eager soon-to-be helpers would be able to carry on the project and we would then see interesting results.

  The first volunteer who took over after we checked on the birds during my two-week absence got radio signals from six of the eight transmitters. The notes he took said, “The birds are consistently in the general vicinity of their nests,” “They are not yet flying great distances, just making small movements in the nest vicinity,” and “They are extremely hard to locate visually.” All was as expected, which was why I didn’t question the data just then.

  Starting June 18, the next volunteer spent five days doing nothing but tracking. Anticipating that the birds would still not have wandered out of radio contact, I asked him to take a compass reading every three to four hours and to write down the directions of the radio signals from specific predetermined spots. In this way, the movements of the birds could be determined more consistently.

  He collected a hefty sheaf of data in five days. He had dozens of radio contacts with each of the same six birds the first helper had found, plus one additional bird. Curiously, the additional bird was found only three times.

  I eagerly plotted the data. Strangely, one signal, Number 8169, was picked up five times at one station only, but always from the same direction. It was not picked up at all during sixteen other readings at the same station. Number 8510 was picked up every single time the student looked for the birds. He found it from one station only, but from various directions ranging from 70 degrees to 28 degrees from magnetic north. The same applied to Number 9680, but at directions varying from 150 degrees to 350 degrees. In short, the data set said that the birds either had stayed at the nests or had moved only locally for very small distances. But most of the time, they were missing!

  As you may have guessed by now, the data didn’t make sense. I needed to enter a swamp and try to find the first and most faintly beeping transmitter with a raven still attached. Coming into a cover of evergreens, I heard a golden-crowned kinglet scolding. What would it be excited about, I wondered. It had found a saw-whet owl, I guessed. And so it was. The little owl made itself slim next to the stem on a spruce and peered down at me with its wide yellow eyes that seemed dark in the shadows.

  Soon I was in a beaver bog. The radio signal became weak all of a sudden; a hill was blocking the signal. A half hour later, I came to another beaver bog with a big lodge near the edge of the new pond the beavers had created. The lodge had freshly chewed sticks on it. A mourning cloak butterfly fed on oozing sap and spread its wings to the sun. A great blue heron fishing from the beaver lodge lifted off and disappeared around the bend of the valley.

  In twenty minutes, I was at the V of the confluence of two brooks. The signal sounded maddeningly close. I searched under a big fir tree and a big birch stump at the water’s edge. Three hours later, try as I might, I still had not found the transmitter. A pile of raven feathers lay right at the edge of the water by the roots of a big upright white birch stump under the tall fir tree. So I knew the bird that had carried the transmitter had probably been killed by a raptor. The signal was very strong next to the fir tree trunk, but my search turned up nothing except more feathers. I tried again. I got a very strong signal by the edge of the brook. I checked under the banks. Nothing. Now the signal was strong at a fallen log nearby. I dug. Nothing. Why did the signal strength keep changing? The signal seemed to be ever so slightly stronger when I tipped the antenna up. (You also get a signal by turning the antenna in the direction opposite to its source.) But I had already dug up the leaf litter and the stream-deposited debris all around. Did that mean the transmitter was up in the air rather than down in the ground? At such a short distance, perhaps alignment of antennae is more important than direction in causing slight changes in signal strength. I was not optimistic that I would find it up in the tree. The top was too dense, and not the place a large owl would choose to pluck its prey.

  Still, I climbed the tree. Halfway up, as I looked down, I realized that if the raven had been plucked up here, the feathers would not be within some five feet of each other below. They’d be scattered all over the place. Besides, the transmitter had a blunt heavy end and no rough spots to catch on limbs. How could it possibly get hung up in branches? The idea that the radio was up there made no sense at all, but I ascended anyway, because I had exhausted my store of logic. Doing stupid things would not, I hoped, prove me stupid. I found nothing, though.

  Later, in defiance of all logic, I climbed the tree once more, having again exhausted all other possbilities. When I got to the top this time, having searched all the branches, I happened to look down over the area below. Then I saw it. Next to the fir tree and just below me was the top of a twenty-foot-high dead birch stub. The transmitter lay balanced on top of the stub. The raptor, probably a great horned owl, must have plucked its prey on the stub, as they are wont to do.

  The next day, I tuned the receiver to another transmitter, heard its constant clicks, and gave chase at a trot. This time with a helper for support, I tried to set a proper field biologist example by traversing a succession of small valleys and hills, crashing through the underbrush. All of the area we traversed had been logged about ten years earlier, and it was a tangle of poplar
saplings, raspberries, blackberries, and fir trees, all sprouting through rotten slash. We sweated and swatted deerflies that burrowed into our wet hair. When we came to muddy brooks, I set a good example and jumped in and waded across. We soon came to old logging roads, where we ran. The signal got stronger as we came over a hill to another big beaver bog. The deerflies may have been bad, but when you’re distracted by mosquitos, mud, and tall wet swale grass, you notice them less. After only an hour, we picked the second radio up off the ground. This one was also attached to the remains of a raven. There were still four other radios to track down, so we ran on.

  All of these four radios, it eventually turned out, also showed similar signs of having lain still for some time. All were attached to long-decayed raven remains.

  In early August, Scott Lindsey, a local schoolteacher, and I climbed to the top of Mount Bald, Mount Tumbledown, and Mount Blue, to do radio surveys of the surrounding countryside. The two radios presumably still at large had at least four more months of life left. But we never got a signal again, even from the mountaintops. Perhaps two out of eight birds were still alive. The statistics that I knew so well were taking on new meaning. These were “my” raven friends and neighbors being killed.

  Raven male who has found a territory and is making his claim through calls that exclude competitors.

  SEVEN

  Settling in a Home Territory

  RAVENS LEAVE HOME AS JUVENILES, wander, and after extensive exploring, settle down to live by the means that their capacities and experiences dictate. Their area of residence becomes their home, and they remain true to it, as far as we know, for most or all of the rest of their lives. They remain true to home for probably the same reasons we do.