Vocabulary

Directions: Scan the following passage and find the words which have roughly the same meanings as those given below. The number in the brackets after each word definition refers to the number of paragraph in which the target word is.

     Do pigeons use their biological clocks to help them find directions from the sun? We can keep pigeons in a room lit only by lamps. And we can program the lighting to produce artificial "days", different from the day outside. After a while we have shifted their clocks. Now we take them far away from home and let them go on a sunny day. Most of them start out as if they know just which way to go, but choose a wrong direction. They have picked a direction that would be correct for the position of the sun and the time of day according to their shifted clocks.
     We have talked about one of the more complex experiments that lead to the belief that homing pigeons can tell directions by the sun. But what happens when the sky is darkly overcast by clouds and no one can see where the sun is? Then the pigeons still find their way home. The same experiment has been repeated many times on sunny days and the result was always the same. But on very overcast days clock-shifted pigeons are just as good as normal pigeons in starting out in the right directions. So it seems that pigeons also have some extra sense of direction to use when they cannot see the sun.
     Naturally, people have wondered whether pigeons might have a build-in compass—something that would tell them about the directions of the earth’s magnetic field. One way to test that idea would be to see if a pigeon's sense of direction can be fooled by a magnet attached to its back. With a strong magnet close by, a compass can no longer tell direction.