Clever Ravens Masters of Deceit
Ravens can toboggan, ride other animals and spy on their enemies. Their life as cadgers stealing prey from wolves, eagles and bears has made them outstandingly intelligent. But do ravens know what they're doing and why? Austrian biologists want to find out.
Those ravens! Their newest form of entertainment is wild boar rodeo. Biologist Mareike Stöwe swears she often sees ravens trotting through the enclosure on the backs of irritated wild boars.
"Ravens like to make an impression," Stöwe says. The birds are always out to perform unusual tricks likely to impress their kin. Dangling head-down from a branch is another popular past-time of theirs.
Ravenologists always have something to laugh about. They're currently observing some common ravens (corvus corax) in large aviaries at the Konrad Lorenz Research Center in Grünau, Austria, where Stöwe works. The play instinct displayed by the birds is tremendous. In the winter time, they tumble down snowy hills. The especially courageous ones grab a boar by the tail and let themselves be towed through the snow on their backs, as if by a drag lift.
And yet the questions explored in Grünau are serious. The most important one is: How intelligent are the animals really?
Their skills when it comes to tricking and cheating, for example, have not been thoroughly explored. Ravens are cunning enough to set up mock hiding places in order to distract their thievish fellows from their real food stores. They're generally very inventive when it comes to tricking those who would snatch away their food. But how much truth is there to reports according to which ravens play dead next to carcasses in order to simulate a case of food poisoning?
Stöwe's colleague Thomas Bugnyar hesitates to believe such reports: "Many animals play dead in stressful stituations," he says. "But when it comes to ravens, everyone always suspects some hidden intention." Bugnyar has been examining numerous winged wise guys, partly in collaboration with US ravenologist Bernd Heinrich. They found that corvus corax has plenty of surprises in store even under strictly controlled laboratory conditions.
One of the trickiest challenges consists in making the raven sit on a bar with a piece of meat suspended vertically below it by a long string. What can the raven do to get at the dangling meal? There is only one solution: The raven has to use its beak to carefully pull the string a short way up. It then has to shape the string into a loop and place one talon on that loop. Then it has to pull the string up a little further and repeat the process. Done properly, the procedure allows the raven to gradually move the meat upward.
Too much trouble for a bird? The smartest ravens examined in Grünau patiently considered the challenge and then pulled the meat up. They discovered the right procedure right away. It seems they mentally rehearsed the problem before getting started.
Quiet premeditation and reflection on possible action represent a pretty high level of intelligence -- one that even primates struggle with sometimes.
The researchers ran a second experiment to rule out errors: The ravens were shooed from the bar the moment they had seized on their dangling booty. Stupid birds would have held on to the meat even though it was still tied to the bar. But most ravens were happy to let it drop: They apparently knew it wouldn't be lost for good. The researchers were finally convinced following a further experiment in which the string was unfastened from the bar. Once the string had been unfastened, the birds flew away with the meat.
The ravens have now passed so many tests the researchers are wondering what purpose all this cleverness serves. Other birds get through life just fine with far less intelligence. A congenital program tells them how to build elaborate nests and sing cheerful songs. But intelligence is -- from a biological view -- laborious and costly. Those who think make mistakes. The question is: Why has evolution made ravens so smart? Why don't they have the luxury of just doing the right thing automatically?
Ravenologist Heinrich has a simple answer: "The right thing hardly exists for ravens." The birds lead an extremely changeful life. In the wild, they live mostly off carrion slain by larger predators. Their survival depends on whether or not they reach the scene of the slaughter in time to grab whatever is there -- usually in the presence of the predator.
It's difficult to imagine a more precarious situation. Wolves, bears and foxes are easily angered when a pesky animal wants to eat their food. One casual snap of the jaws, and things are over for the raven. The bird needs to be able to assess just how far it can go at any moment. It always needs to consider the question of what is going through the minds of the larger beasts whose food it is stealing.
In such dangerous situations, where nothing is predictable, a rigid program of behavior would spell certain death. That's why ravens already acquire the art of flexibility during the first weeks of their lives. Barely fledged, they display an almost pathological curiosity for everything that can be pecked at and tweaked. Most importantly, they're driven by a powerful desire to annoy dangerous predators. The squabs repeatedly land near bears or wolves and approach them quietly from behind.
The art of flexibility
Bernd Heinrich has repeatedly seen young ravens tweaking the tail of a wolf and then immediately jumping away with wings flapping. That way, the birds gradually determine the point at which audacity becomes life-threatening -- as well as acquiring a sense of how far the animal they are taunting can jump in one leap. Young ravens engage in these activities despite the fact that they are visibly terrified of the predators. "It's not a senseless game," Heinrich concludes, "but a congenital drive."
Grown ravens are already so skilful at interpreting the behavior of other animals they usually get most of the prey. Up to 90 percent of the slain animal goes to the black-feathered nags. "So far, ravens have been grossly underestimated as carrion consumers," says Thomas Bugnyar. "They don't just grab the leftovers: They get almost everything."
It seems that from the point of view of the winged slyboots, large predators are little more than simpletons. Wherever such predators have slain their prey, ravens are quick to appear on the scene, as efficient as a clean-up squad. They don't even waste any time eating. Whatever they can get their beaks around is swiftly taken away and carefully hidden in the surrounding landscape - to be enjoyed later. That's why even large carcasses have often already been fully ransacked within half a day.
Ravens especially like working with wolves. Sometimes they'll croak loudly to direct a pack of wolves to weak game they couldn't themselves attack. Researches who have examined this kind of cooperation even suspect wolves are driven to hunt in packs mainly because of the ravens. The predators are good sprinters and could theoretically slay game the size of deer alone or in pairs. But they would harldy get any meat for themselves during the feast that follows the slaying, due to the superior number of ravens.
When ravenologist Heinrich once experimentally placed two cow carcasses on the ground, he counted a total of 500 ravens that arrived to feast on the meat. "Some of them must have arrived from hundreds of miles away," Heinrich says. "The restaurant was obviously well advertized."
The mobile younger ravens, who ramble about in loose flocks, are in charge of spreading information. When they discover carrion, they immediately begin croaking to their companions, who rush to the scene. It's only that way that the young ravens stand a chance against their elders, life-long pairs of which rule over vast territories. The gangs of young ravens bet on the power of superior numbers, and the rulers of the local territory are often left out to dry.
But companionship ends as soon as the prey has been secured. There is no sharing. Every animals puts as much meat aside for private consumption as possible. What is more, the smarter ones prefer letting others work for them, spying on their hiding places in order to plunder them as soon as an opportunity arises.
But few ravens are stupid enough to just let themselves be watched as they hide their prey. So the lurking thief must under no circumstances arouse the suspicion of its victim: "He has to restrain himself with iron discipline until the other has finally left," says Bugnyar. "That's an incredibly difficult thing for an animal to do."
Ravens can do it. They have a long evolutionary process of espionage and counter-espionage to build on, in the course of which they became masters of deceit and problem-solving. They got better and better at guessing the intentions of others and concealing their own. "Ravens are cognitively equal to a two-year-old child," says Bugnyar.
The birds are highly sophisticated when it comes to assessing their adversary's degree of knowledge and considering it for the purpose of their deeds and misdeeds. They won't attribute much brainpower to a wolf, for example. "When ravens discover a wolf burying a piece of meat, they watch him openly, "Bugnyar reports. "And when he leaves, they just dig it up." But when it comes to their conspecifics, who are prepared for such tricks, they act demonstratively uninvolved, grooming their feathers and stilting about as if bored.
Bugnyar discovered that thieving ravens even spy on each other when searching for goods to steal. A raven will remember the other ravens that, together with it, witnessed the hiding of the meat. On top of that, it remembers which raven is likely to have seen which hiding place, and acts accordingly: Hiding places not far from other ravens who may also be in the know are plundered first. The others can wait.
Such intricate strategic planning requires ravens to consider things from various points of view. It's almost a question of seeing through the eyes of others. That's a skill ravens share with the cleverest primates. But do ravens also know what they're doing and why? Or have they just developed an extraordinary cunningness in the struggle for food during the course of their evolution?
In search of an answer to this question, Bugnyar next wants to investigate whether the birds also display intelligence in other contexts. At the research center in Grünau, things look very much as if that were the case. Ravens cultivate a rich social life, especially prior to sexual maturity, when they live in groups. And they deliberately forge alliances in their quest for certain positions. Ravens that have befriended each other stick together in conflict situations, and they don't steal from each other quite as unrestrainedly.
Ravenologist Stöwe has even observed gestures of consolation. When one raven has lost out in an argument, the other appeasingly runs its beak between the loser's feathers. "It's touching to see what gentleness these mighty beaks are capable of," says Stöwe.
The biologist is a long way from growing bored of the lively birds with their searching spirit. "They look at everything we do so carefully," Stöwe says. "We're really the ones under observation."