Researchers have found that migrating animals use a variety of inner compasses to help them navigate. Some (1) by the position of the Sun. Others navigate by the stars. Some use the Sun as (2) guide during the day, and then (3) to star navigation by night. One study shows that the homing pigeon uses theEarth’s magnetic fields as a guide (4) finding its way home, and there are indications that various other animals, from insects to mollusks (软体动物), can also make (5) of magnetic compasses. (6) is of course very useful for a migrating bird to be able to switch to magnetic compass when clouds cover the sun; (7) it Would just have to land and wait for the Sun to come out again. (8) with the Sun or stars to steer by, the problems of navigation are more complicated (9) they might seem at first. For example, a worker honeybee (10) has found a rich source of nectar and pollen flies rapidly home to the hive to (11) :A、naturalist has discovered that the bee scout (12) her report through complicated dance in the hive, (13) she tells the other workers not only how far away the food is, but also what direction to fly in (14) to the Sun. (15) the Sun does not stay in one place all day.As the workers start (16) to gather the food, the Sun may (17) have changed its position in the sky somewhat. In later trips during the day, the Sun seems to move farther and farther toward the west. Yet the worker bees seem to have no (18) at all in finding the food source. Their inner (19) tell them just where the Sun will be, and they change their course (20) .
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