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.
中考英语满分作文:未来的生活
初三英语作文:谈谈运动
初三英语作文:乒乓王子孔令辉
初三英语作文:Colorful Life
初三英语作文:Buying pictures
中考英语满分作文:我爱我的家
初三英语作文:写给同学的信
中考英语满分作文:A meaningful Mid-autumn Day
初三英语作文:Going online
初三英语作文:孩子的独立教育
初三英语作文:No smoking, please
初三英语作文:初中写作中常见的十二种句型2
初三英语作文:Young volunteers
中考英语书面表达精品习作欣赏 1
“十字箴言”帮你搞定中考英语写作
初三英语作文:初中英语书面表达易错表达大全 1
初三暑假英语周记 4
中考英语书面表达精品习作欣赏 2
初三英语作文:再见 祝你好运
初三英语作文:Books and I are good friends
初三英语作文:快乐暑假
中考英语满分作文:An old pear tree
初三英语作文:My views on English
初三英语作文:Jane的国庆节之行
初三满分英语作文赏析
初三英语作文:做三明治的过程
中考英语满分作文:Bill的生活习惯
初三英语作文:Life in the dormitory
中考英语满分作文:My grandfather
初三英语书面表达写作常识 1
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |