Mind of the Raven: Investigations and Adventures With Wolf-Birds (20 page)

Preliminary studies revealed that ravens were indeed near or sometimes even in fields where sheep or cattle were giving birth, which was proof enough for those wishing for a cash reimbursement for dead cattle. In northern Germany farmers were, unlike in former times, allowing calving to occur out of doors in the winter, and farmers got cash
for dead calves or lambs. Ever more livestock was found in the pastures with their eyes and tongues pecked out, and ravens were as before in attendance. It was an opportunity with something for everyone—the news media, the farmers, the Jäger, the politicians, and even the biologists. When asked to give comments and advice, I said that at least one documentation of a raven killing a cow might be handy. Ravens would feed on afterbirths and on dead or dying lambs. Luckily, our cattle and sheep in New England give birth inside barns, so that ravens cannot be blamed for the innumerable calves that die on their own during birth.

Ravens and other corvid birds have long been persecuted in Germany by the Jäger, a well-organized group that proudly think of themselves as keepers of the natural order. In a disturbed ecosystem that no longer has its natural predators, they do indeed justifiably control deer and boar populations that would otherwise inhibit regeneration of trees, remove underbrush, disturb soil, devastate crops, and affect breeding bird populations. They traditionally also persecute the corvid birds because they are nest predators on other birds. With this latest uproar, the Jäger were clamoring to have the raven taken off the endangered list, so that they could again be shot as in former times, when they were almost totally obliterated from the whole country.

When I visited Germany in 1996, ravens were still getting bad press, and Dieter Wallenschläger, professor of animal ecology and nature conservation at the University of Potsdam, undertook an investigation. We corresponded about the public menace. I personally was dubious of the killer raven stories, because the ravens I was familiar with are cautious even of unattended carcasses. Finding one, they jump up and down in front of it, as if to provoke a reaction. Although I suspect veterinarians have even better means of detecting life, the raven’s method neatly discriminates healthy from just barely alive or dead animals. They would not normally touch a calf that moved, although it is possible that if ravens were to feed often enough on dead or nearly dead calves, they might eventually learn to feed on half-dead ones with less hesitation. Seeing a bird in the act of picking an eye from a dying calf, one might well believe the raven was the cause of the calf’s death.

Dieter heard I was visiting Berlin, and invited me to come to Potsdam. Not only that, he organized a mini-symposium with the title, roughly translated: “Killer Ravens in Brandenburg—Legend or Occupation of a New Ecological Niche?” I was glad to attend. After the introductions, a farmer, Frau Breme, talked of the results of her recent 1996 questionnaire of raven damages that she had sent out to 141 farmers. She got seventy-one returns. Of those, fifty farmers saw ravens, and 41 percent of those saw “
Veränderungen”
(changes) of animals; i.e., ravens feeding on an animal. In the ensuing discussion of this report, I mentioned the high mortality of calves in New England and the high percentage of
Veränderungen
of these calves by my ravens, despite absolute proof that these ravens had not killed the calves. German nature conservation people agreed that there was so far not one proven case of a raven causing the death of a healthy calf.

The government had by now eventually insisted on proof of cause of death before making cash reimbursements. Veterinarians were consulted to make autopsies. Certain examinations of lungs and eyes of newborn calves could determine if the animal had been able to stand when born. Given the examinations, almost all of the calves
verändert
by ravens had something wrong with them to begin with. They were mostly found to belong to careless farmers who did not take adequate care of their animals. Good farmers didn’t have a raven problem. After the government finally insisted on proof, and after none was forthcoming, the raven damage subsidy became unavailable. Money to study ravens evaporated as well.

The ravens’ dependence on large animals is central to their biology. When we were hunters, ravens were revered companions who inspired poets and engendered creation myths. The presence of ravens meant large animals were near. They meant meat and merriment. All that changed when we became settled herders. Ravens soon became a suspected destroyer of lambs, and prophets of doom and gloom. They were relentlessly persecuted because they were
associated
with death, although not, as it now seems since scientific study, because they caused it. Ravens’ physical power to kill had been overestimated; and the subtleties of their responses, where their real power lies, underestimated.

I
N MANY SEABIRDS, BATS, AND OTHER
colonial species in which parents leave their young among others, there is much opportunity for accidentally feeding others’ young instead of one’s own. These animals have evolved to be capable of identifying their own offspring in a crowd, and they reserve their precious food offerings strictly for them. I wondered how ravens would react to missing or extra young. Could they count? Otto Koehler and his colleagues at Freiburg University in Germany had concluded that they could count to seven, having trained a raven to retrieve food under one of several covered vessels, after training it to expect the food in only one container that had the correct number of spots on the lid.

I played a numbers game with Houdi in Vermont, using her four young when they were already partly feathered-out toddlers at near-adult weight. While she was out foraging from a calf carcass I’d left nearby in the woods, I would rush out my bedroom window to her nest and bring two of them back inside. The little birds were still too young to be alarmed. They were at an age when they remained calm as long as they did not hear the parents’ alarm calls. Since Fuzz, her mate, was missing, I could be confident no parent had seen me handling the young. When she returned to the nest with half her brood missing, she fed her young in several seconds as always, then hopped to the water tray for a drink, perched nearby to preen and shake, and then went out of the aviary to the calf carcass for another load of meat. As soon as she was out of sight, I rushed out and took the other two young, replacing the first two. When she came back, she again made no vocalizations and showed no emotion. I offered her a chicken egg. She took it eagerly, cracked it, and fed the two young three times. After she left the nest, I replaced the second pair of young to complete the clutch to four. Houdi again showed no reaction to the sudden change in the number of her brood. For all appearances, Houdi didn’t count, didn’t care, and/or didn’t recognize the difference in appearance of a nest with two versus four young.

As I explained earlier, Houdi’s four young later were orphaned. The responsibility of tending to the ravenous quadruplets that required hourly attention was not on my agenda at that time. I sought to pawn off my responsibility and hoped to do an experiment at the same time. Goliath and Whitefeather in Maine had only two offspring, though much younger and still naked. Would they accept Houdi’s four orphans in spite of the age difference?

I drove to Maine on May 6, and delivered Houdi’s four feathered young into Goliath and Whitefeather’s nest in the middle of the night so that they would not see what was happening, temporarily replacing the two much younger offspring of Goliath and Whitefeather. I took their own young out because I feared the parents might compare the newcomers against their own, and then reject and harm them. I went into the nearby observation hut at dawn to watch what would happen.

By 5:10
A.M.
, it had been light for at least ten minutes, and the pair perched quietly in the shed by the nest. They could not help seeing the four new strange young in their nest, nor miss that their own two were missing, but they showed no visible reaction.

At 5:29, one young began to beg. Whitefeather stretched. Another young began to beg. Ten minutes later, when the sun first peeked over the ridge and shone directly into the nest shed, the adults suddenly stood immobilized like statues. The young were silent, and their blue eyes blinked as their heads rested on the nest rim. The adults stood as if dumbstruck, intently examining the young. Both moved their heads quizzically from side to side, looking at the young in their nest first with one eye, then with the other from a different angle. Several young soon stood up and begged. Whitefeather’s head then went fuzzy. She was agitated. At first tentatively, then vigorously, she started making
kek-kek-kek
alarm calls. The young, responding to her noise and movement, begged even more. She then made pecking motions at their heads, vigorously gesticulating her anger without hitting them. With her head still fuzzy, she partially opened her bill, as birds do when frightened or alarmed. This was not going as I had hoped. She was not happy. Goliath, in contrast, showed no reaction.

Five minutes later, both birds finally flew out of the nest shed and made long and rapidly repeated rasping alarm calls, such as when an intruder comes near. Whitefeather started hammering at branches in anger, and she also hung upside down by her feet from the wire screening. I had never seen her do either of these behaviors before. I then came out of hiding from my observation shed and sought to blunt their anger by bringing a roadkill. Both birds greeted me (and the dead beaver) without alarm, and both immediately fed. They then began to carry loads of meat up to the nest. The young begged unabashedly, and Whitefeather now readily fed them as if she had completely forgotten her alarm of a few minutes earlier. I was flabbergasted. The four strange young were apparently going to be adopted after all.

It then seemed safe and appropriate to return Goliath and Whitefeather’s own young back to the nest, making it a clutch of six. Would
the ravens now preferentially feed their own? To the contrary, in the first thirteen feeding trips to the nest, twelve by Whitefeather and one by Goliath, all of the food went to Houdi’s young, not their own babies. Whitefeather probably simply fed the loudest and most insistent beggars, apparently finding a big pink open mouth irresistible. After the young stopped begging, she stood at the nest edge looking at them, repeatedly making soft low
krr-krr
sounds that induce hungry young to gape. She was making sure they had enough. Goliath was soon also feeding all the young. The question, and my dilemma, had been resolved: Whitefeather and Goliath had totally accepted the newcomers. Throughout the next few months, I brought them other treats besides the beaver carcass, but the pair were now on their own, and they successfully reared “their” six young to independence.

The next year, in spring 1997, Goliath and Whitefeather had started to rebuild their nest in the aviary, but they later abandoned the breeding attempt. I brought other young ravens I was then rearing for later observations and experiments to test insight, curious to see if these would also be openly received. At first, I kept these youngsters inside the cabin. Goliath responded quickly to their loud begging when I fed them. He came and perched on the birch tree outside the cabin, making long, high-pitched, trilling, upward-inflected alarm calls. He came several times right next to the cabin, as if wanting to come in, exhibiting the male dominance display with fuzzy head, bill-snapping, and bowing simultaneous with flaring his tail and wings.

On this same day, I had seen him chase a red-tailed hawk, giving the rapid staccato calls normally given to aerial predators. When three turkey vultures had come by, he immediately flew to the nest by the aviary, making sharp alarm calls and fluffing himself out. Other ravens had come, and he had vigorously chased them off as well.

I finally brought two of the young, nearly grown ravens out of the cabin and let them hop around on the picnic table. As the young begged from me, Goliath, perched right next to me in the top of the dead birch, showed anger. He stared at the youngsters and made single long calls, one after another, with a high pitch and an upward-inflection normally given as a territorial advertisement. He flew over
the youngsters, who ducked and momentarily stopped their begging. Next, he perched forty yards away in a spruce tree, puffed himself out, and angrily attacked cones and branches, hacking them off. Curiously, he made no attempt to hop onto the table to harm the young.

Ravens and most other birds have not evolved behavior to reject young from their own nests, even when these young may look odd to them, because foreign young would normally almost never be deposited there. It is sometimes a different story with eggs that could become stranger’s young. An egg could be laid into a neighbor’s nest accidentally, and some bird species specialize in parasitizing other parents by dumping their eggs off to surrogate parents. They no longer build any nest of their own. The best-known examples of this are cuckoos in the Old World and cowbirds in the New.

As is usual in evolution, almost every strategy has a counter-strategy aimed at neutralizing it, and so on in a continuing tit-for-tat game that continues until a mutual balance is reached in a messy “real world,” or continuing until one of the contestants becomes extinct. In birds, the arms race between bird nest parasites and their hosts is played out largely with egg color. There is the strategy of color matching to deceive by the parasites, pitted against that of detection of color differences to recognize deception, in what is a classic example of coevolution, where one species evolves in response to another or others. The variety and the beauty of the coloring of birds’ eggs is one of the marvels of nature, and it is likely the outcome of the conflict between egg-dumping parasites and their hosts of those birds with open nests where the eggs are visible (most hole nesters have uncolored eggs).

At the population level, color variety between
species
creates difficulties for the local nest parasites, and such differences could easily evolve. For example, if one parasite species specializes to dump its eggs into victims with blue eggs, say species A, B, C, and D, then an individual bird of one of these victim species C would be protected if it has a mutation that results in the production of eggs with purple speckles. That mutation would then quickly spread, and individuals of that species would eventually all have purple-speckled eggs.

At the present time in evolution, the arms race in egg coloring in songbirds has resulted in a great variety of egg colors. Most familiar to us in North America, for example, are robins with pale blue eggs, phoebes with pure white eggs, and kingbirds with white eggs spotted and blotched with purple, black, and lavender. Similar color variety among species exists in the eggs of European birds. In Europe, the common cuckoo is the main egg parasite. The cuckoo’s eggs closely match their hosts’ eggs. They need to. If cuckoos laid white eggs in Europe, they could not parasitize birds laying blue eggs, because those species, after a long history of parasitism, would instantly recognize a white egg among a clutch of their own that are all blue. The cuckoo would lose that unmatched egg, and that line of cuckoos who persist in laying white eggs into nests with blue eggs would go extinct. In Europe, the outcome has been that each female cuckoo lays eggs of only one color, and lays her eggs in only the “correct” species—the one with those colors that her eggs will match. However, the population of cuckoos has different individuals who lay different-colored eggs, and who dump their eggs in species providing an appropriate match. Of course, as expected, the eggs don’t always match perfectly—and some of the hosts, some of the time, are able to detect an off-color egg and toss it out, because in Europe the chances of an off-color egg being a cuckoo’s is great. The host’s chances of making a correct choice—tossing out the cuckoos’ and not their own egg—increase enormously if it does two things: memorize what its first-laid egg looks like, and have all eggs of its own clutch look nearly alike. That is the case.

Ravens have greenish-blue eggs variously mottled with grays and blacks. They are often, but not always, quite variable within any one clutch, so given the rationale explained above, it seems unlikely that raven egg coloration has been standardized to provide a uniform background against which a strangers’ eggs would stand out. In North America, there are no raven nest parasites, so there is no reason to suppose that common ravens have evolved egg-rejection behavior. They might still recognize a strange egg, but they face no risk of raising a stranger’s young and the cost of making a mistake and ejecting one of their own is great. Evolutionary logic therefore dictates that
while they should defend their nest from possible egg-dumping females, a strange-looking egg should
not
be ejected, because it is most likely one of their own.

I decided to experiment with egg recognition. I began by trying to climb to the raven nest at the Melcher farm, where I knew the birds should be incubating, and to give them a chicken egg. At Melcher’s barn, I stopped to talk with Paul about his raven nest, then crossed his large rolling field, still covered with snow, and went on down to the brook at the other side. The brook was gurgling loudly underneath bridges of ice. Crossing one of these ice bridges, I ascended the steep hill on the other side through woods shaded by tall hemlocks. A pair of ravens had built their nest for tens of years in a grove of tall white pines near the top of the hill. Having seen the pair circle over the hill earlier in the spring, I expected to find the nest again.

The birds’ staccato
kek-kek-kek
alarm calls commenced as I came close to the pines. To my surprise, the huge stick structure was on the very same spot it had been several years ago.

When I finally made it up to the solid live branches just beneath the nest, I was exhausted, but my spirits soared. The nest contained six eggs. These, like most raven eggs, were in a deep nest cup of shredded cedar bark and tufts of deer and cattle fur, all mixed together with the shredded inner bark of dead ash trees. The eggs were greenish-blue with a variety of irregularly shaped gray and black spots and blotches. Some of the dark spots had an olive tint, others were faintly purple. The spots and blotches varied from a smoky haze of gray to black, and ranged in size from much smaller than a pinhead to larger than a housefly. Little Houdi’s, the six eggs were individually distinct. Some of them showed a background color of light blue-green, and in others most of this background was obscured by dense blotching of dark olive green. I could hardly imagine anything more beautiful, nor could I suppose any more tangible evidence that these birds likely did not have a long history of egg parasitism. These eggs were too variable in color.