標準環境・自然科学

Crows and Their Tools

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For a long time, using tools was thought to be something that only human beings did. Later, researchers found that chimpanzees push sticks into holes to catch insects, and the of a tool had to be made wider. Birds were not expected to join this group, because their brains are small. However, crows living on the island of New Caledonia in the Pacific Ocean have surprised scientists. They cut leaves into narrow shapes with sharp edges and use them to pull insects out of holes in trees. In one , a crow named Betty was given a small bucket of food at the bottom of a tube. Two pieces of were placed , one straight and one already bent into a hook. When another bird took the hooked away, Betty pushed the straight against the side of the tube and bent it herself. She then used it to the bucket out. She had never been taught to do this, and she repeated it many times afterward. Young crows do not know how to make tools when they are born. They stay with their parents for a longer than most other birds, sometimes for more than a year, and they watch while the adults work. At first they hold the leaves in the way and drop them, and in one study a young bird spent almost a hundred days practicing before it produced a tool that worked. Researchers have also noticed that crows in different valleys make tools of different shapes. This suggests that the birds copy the birds around them rather than alone. Not everyone agrees about what these findings mean. Some scientists out that most experiments are carried out with birds kept in cages, where the animals have plenty of time and food and nothing else to do. Wild crows may differently. Others that judging animals by how they act like humans may be the . A crow that cannot solve a puzzle designed by people may still be highly skilled at the problems that matter in its own .