Надо составить 12 вопросов к текст: some creatures have built-in compasses. imagine that you are sitting in a canoe on a dark and cloudy night in the middle of a big lake. you are completely lost. you have no idea of which way to paddle or where you might get by paddling in any one direction. while you are worrying about what you might do, think about the many other creatures that would have no problem at all. a long list of animals as different as birds, bees, fish, turtles, and whales would know right off what direction would take them home. for more than twenty years scientists have been seeking to understand the mystery of this “sixth sense” of direction. by trying out ideas and solving problems one by one, they are now getting close to an answer. one idea that is fun to think about is that animals might have a built-in compass. our earth is itself a big magnet. so a little magnetic needle that swings freely will line itself up with the big earth magnet to point north and south. when people discovered that idea about a thousand years ago and invented the compass, it became a new high-tech gadget. it allowed sailors to navigate on ocean voyages, even out of sight of land and under cloudy skies. birds find their way actually the idea of an animal compass came just from observing animals in nature. many birds migrate between their summer homes and their winter homes twice a year. some of them fly for thousands of miles and mostly at night. experiments have shown that some birds can recognize star patterns. but they can keep on course even under cloudy skies. how can they do that? a common bird that does not migrate but is great at finding its way home is the homing pigeon. not all pigeons can find their way home. those that can are very good at it, and they have been widely studied. one neat experiment was to attach little magnets to the birds’ heads. the idea was to try to block the magnetic sense—just as a loud radio can keep you from hearing a call to supper. on sunny days, that did not fool the pigeons. evidently they can use the sun to tell direction just as people can. but on cloudy days, the pigeons with magnets could no longer find their way. it was as if the magnets had blocked the birds’ magnetic sense. similar experiments with the same kind of results were done with honeybees. these insects also seem to have a special sense of direction. in spite of these experiments, the idea of an animal compass seemed pretty far out. how would an animal get the magnetic stuff for a compass?

bogdan345710    1   14.07.2019 02:50    2