Researchers have found that migrating animals use a variety of inner compasses to help them navigate. Some steer by the position of the Sun. Others navigate by the stars. Some use the Sun as their guide during the day and then switch to star navigation by night. One study shows that the homing pigeon uses the Earths magnetic fields as a guide in finding its way home and there are indications that various other animals from insects to mollusks, can also make use of magnetic compasses. It is of course very useful for a migrating bird to be able to switch to a magnetic compass when clouds cover the Sun; otherwise it would just have to land and wait for the Sun to come out again. Even with the Sun or stars to steer by, the problems of navigation are more complicated than they might seem at first. For example, a worker honeybee that has found a rich source of nectar and pollen flies rapidly home to the hive to report. A naturalist has discovered that the bee scout delivers her report through a complicated dance in the hive, in which she tells the other workers not only how far away the food is, but also what direction to fly in relation to the Sun. But the Sun does not stay in one place all day. As the workers start out to gather the food, the Sun may already have changed its position in the sky somewhat. In later trips during the day, the Sun will seem to move farther and farther toward the west. Yet the worker bees seem to have no trouble at all in finding the food source. Their inner clocks tell them just where the Sun will be and they change their course correspondingly.
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2017届高考英语一轮单元复习精讲课件：第1部分 必修5 Unit5《First aid》（人教版新课标）
2017届高考英语一轮复习分层限时跟踪练：必修5-Unit 1《Great scientists》（人教版新课标含解析）
2017届高考英语一轮单元复习精讲课件：第1部分 必修2 Unit5《Music》（人教版新课标）
2017届高考英语一轮复习分层限时跟踪练：必修3-Unit 5《Canada－“The True North”》（人教版新课标含解析）
2017届高考英语一轮复习分层限时跟踪练：必修5-Unit 5《First aid》（人教版新课标含解析）
2017届高考英语一轮复习分层限时跟踪练：选修6-Unit 2《Poems》（人教版新课标含解析）
2017届高考英语一轮单元复习精讲课件：第1部分 选修7 Unit5《Travelling abroad》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 选修7 Unit4《Sharing》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修4 Unit3《taste of English humour》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修3 Unit1《Festivals around the world》（人教版新课标）
2017届高考英语一轮复习分层限时跟踪练：必修3-Unit 2《Healthy eating》（人教版新课标含解析）
2017届高考英语一轮单元复习精讲课件：第1部分 选修8 Unit3《Inventors and inventions》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修5 Unit4《Making the news》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修5 Unit3《Life in the future》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修3 Unit2《Healthy eating》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 选修6 Unit3《Ahealthy life》（人教版新课标）
2017届高考英语一轮复习分层限时跟踪练：必修5-Unit 2《The United Kingdom》（人教版新课标含解析）
2017届高考英语一轮单元复习精讲课件：第1部分 必修4 Unit1《Women of achievement》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 选修8 Unit1《Aland of diversity》（人教版新课标）
2017届高考英语一轮复习分层限时跟踪练：必修5-Unit 4《Making the news》（人教版新课标含解析）
2017届高考英语一轮单元复习精讲课件：第1部分 选修8 Unit2《Cloning》（人教版新课标）
2017届高考英语一轮复习分层限时跟踪练：必修3-Unit 1《Festivals around the world》（人教版新课标含解析）
2017届高考英语一轮单元复习精讲课件：第1部分 选修6 Unit1《art》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修5 Unit1《Great scientists》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修3 Unit4《Astronomy the science of the stars》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修2 Unit4《Wildlife protection》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 选修6 Unit2《Poems》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修5 Unit2《The United Kingdom》（人教版新课标）
2017届高考英语一轮单元复习精讲课件：第1部分 必修4 Unit5《Theme parks》（人教版新课标）
2017届高考英语一轮复习分层限时跟踪练：必修4-Unit 2《Working the land》（人教版新课标含解析）