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  3. Bird Brains Cracking Walnuts The scene: a traffic light crossing on a university campus in Japan. Carrion crows and humans l

Bird Brains Cracking Walnuts The scene: a traffic light crossing on a university campus in Japan. Carrion crows and humans l

admin2010-08-21  25
问题                                            Bird Brains
Cracking Walnuts
    The scene: a traffic light crossing on a university campus in Japan. Carrion crows and humans line up patiently, waiting for the traffic to halt. When the lights change, the birds hop in front of the cars and place walnuts, which they picked from the adjoining trees, on the road. After the lights turn green again, the birds fly away and vehicles drive over the nuts, cracking them open. Finally, when it’s time to cross again, the crows join the pedestrians and pick up their meal.
    Biologists already knew the corvine family--it includes crows, ravens, rooks, magpies and jackdaws--to be among the smartest of all birds. But this remarkable piece of behavior would seem to be a particularly acute demonstration of bird intelligence.  Researchers believe they probably noticed cars driving over nuts fallen from a walnut tree overhanging a road. The crows already knew about dropping clams from a height on the seashore to break them open, but found this did not work for walnuts because of their soft green outer shell.
    Other birds do this, although not with quite the same precision. In the Dardia Mountains of Greece, eagles can be seen carrying tortoises up to a great height and dropping them on to rocks below.
Do Birds Have Intelligence?
    Scientists have argued for decades over whether wild creatures, including birds, show genuine intelligence. Some still consider the human mind to be unique, with animals capable of only the simplest mental processes.  But a new generation of scientists believes that creatures, including birds, can solve problems by insight and even learn by example, as human children do. Birds can even talk in a meaningful way.
Good Memory
    Some birds show quite astonishing powers of recall. A type of North American crow may have the animal world’s keenest memory.  It collects up to 30,000 pine seeds over three weeks in November, and then carefully buries them for safe keeping across over an area of 200 square miles. Over the next eight months, it succeeds in retrieving over 90 percent of them, even when they are covered in feet of snow.
Making and Using Tools
    On the Pacific island of New Caledonia, the crows demonstrate a tool-making, and tool using capability comparable to Paleolithic man’s. Dr Gavin Hunt, a New Zealand biologist, spent three years observing the birds. He found that they used two different forms of hooked "tool" to pull grubs from deep within tree trunks. Other birds and some primates have been seen to use objects to forage. But what is unusual here is that the crows also make their own tools. Using their beaks as scissors and snippers, they fashion hooks from twigs, and make barbed, serrated rakes or combs from stiff leathery leaves. And they don’t throw the tools away after one use--they carry them from one foraging place to another.
    Scientists are still debating what this behavior means. Man’s use of tools is considered a prime indication of his intelligence, is this a skill acquired by chance? Did the crows acquire tool making skills by trial and error rather than planning? Or, in its ability to adapt and exploit an enormous range of resources and habitats, is the crow closer to humans than any other creature?
    Dr Hunt said this of his research: "There are many intriguing questions that remain to be answered about crows’ tool behavior. Most important would be whether or not they mostly learn or genetically inherit the know-how to make and use tools. Without knowing that it is difficult to say anything about their intelligence, although one could guess that these crows have the capability to be as clever as crows in general."
    The woodpecker finch is another consummate toolmaker; It will snap off a twig, trim it to size and use it to pry insects out of bark. In captivity, a cactus finch learnt how to do this by watching the woodpecker finch from its cage. The teacher helped the pupil by passing a ready- made spine across for the cactus finch to use.
Communication Ability
    Another sign of intelligence, thought to be absent in most non-human animals, is the ability to engage in complex, meaningful communication. The work of Professor Irene Pepperberg of the University of Arizona, Tucson, has now shown the general perception of parrots as mindless mimics to be incorrect.
    The captive African grey parrot Alex is one of a number of parrots now believed to have the intelligence and emotional make-up of a 3 to 4 year old child. Under the tutelage of Professor Pepperherg, he acquired a vocabulary of over 100 words. He could say the words for colors and shapes and, apparently, use them meaningfully. He has learned the labels for more than 35 different objects; he knows when to use "no," and phrases such as "come here," "I want X," and "Wanna go Y."
    A bird’s ability to understand, or speak, another bird’s language can be very valuable. New Zealand saddlebacks occupy the same territory for years. They have distinct song "dialects" passed on through the generations. New territory vacancies are hard to find, so young males are always on the look-out for new widows into whose territory they can move. While they wander around the forest, they learn the different dialect songs, just as we might learn a language or develop a regional dialect. As soon as a territory-owning male dies, a new young male may move in to take over within 10 minutes. He will immediately start singing the dialect of the territory he is in.
Possessing Abstract Concepts
    Intelligence--if this is what scientists agree these birds possess--is not limited to the birds we always thought of as "bright." In recent experiments at Cardiff University in Britain, a pigeon identified subtle differences between abstract designs that even art students did not notice. It could even tell that a Picasso was not the same as a Monet. The experiment seems to show that pigeons can hold concepts, or ideas, in their heads. The visual concept for the pigeon is Picasso’s painting style.
Social Necessity Makes Birds Smart.
    Scientists believe it is not physical need that drives creatures to become smarter, but social necessity. The complexities of living together require a higher level of intelligence. Corvids and parrots, along with dolphins, chimps, and humans are all highly social--and smart--animals.
    Some ravens certainly apply their intelligence for the good of the flock. In North America, they contact other ravens to tell them the location of a carcass(动物尸体). Ravens are specialized feeders on the carcasses of large mammals such as moose during the harsh winter months of North America. The birds roost together at night on a tree, arriving noisily from all directions shortly before sunset. The next morning, all the birds leave the roost as highly synchronized(同步地) groups at dawn, giving a few noisy caws, followed by honking. They may all be flying off in the direction taken by a bird, which had discovered a carcass the previous day. This bird leads the others to his food store, apparently sharing his finding with the rest of the flock.
    Ravens share information about their findings of food carcasses because dead animals are patchily(散落地) distributed and hard to find. Many eyes have a better chance of finding a carcass, and once one has been located, the information is pooled(共享的). Although the carcass now has to be shared between more individuals, the heavy snowfall and risk of mammal scavengers (食腐动物) taking the food mean that a single bird or a small group could not eat it all alone anyway.
Intelligence Inheritance
    The level of intelligence among birds may vary. But no living bird is truly stupid. Each generation of bird’s that leaves the protection of its parents to become independent has the inborn genetic information that will help it to survive in the outside world and the skills that it has learned from its parents. They would never have met the challenge of evolution without some degree of native cunning. It’s just that some have much more than others.  
The example of the Japanese carrion crows at the beginning of the passage is a demonstration of the ______.
选项 A、kindness of people
B、harmonious living conditions
C、ecological stability
D、bird intelligence
答案D
解析 由“Cracking Walnuts”部分第二段第二句“But this remarkable piece of behavior would seem to be a particularly acute demonstration of bird intelligence．”可见乌鸦借助交通工具轧碎核桃的行为是鸟类具有智慧的例证。故本题正确答案为D项。
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