Animals' Compasses

 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 Earth's 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.

動物的羅盤

 研究人員已經發現遷徙性動物可以借助各種各樣的體內羅盤來校正方向。  有些動物借 助太陽的位置辨別方向，有些則依靠星星。

 還有的白天利用太陽，晚上利用星星。  有研究 發現信鴿以地磁場為向導來找到回家的路。  還有跡象表明許許多多其它生物，從昆蟲到軟

體動物，也能利用這種磁場羅盤。  具有這種磁場羅盤，對候鳥來說當然非常有用，因為如

 果烏云遮日，它可以以磁場為向導繼續飛行，否則它就只好著陸，等待太陽重新出現。  即 使是借助太陽或星星導航，其中的學問也比它表面看起來的要復雜得多。

 例如，一只工蜂 找到了花圃蜜園，急忙飛回蜂房報信。博物學家發現這只蜂探在蜂房里跳了一段極為復雜的

 舞，通過這段舞她不但告訴其它工蜂食物有多遠，而且報告了以太陽為參照的飛行路線。 但 太陽不會呆在天上不動。

 當蜂群出發采食時，太陽可能已經多少改變了它在天空中的位置。 出發得越遲，太陽就越偏西，可這似乎沒給尋找食物源的工蜂們帶來任何不便。  它們體內

的時鐘告訴他們太陽應在的位置，據此它們相應地改變前進的方向。

譯路通武漢翻譯公司

2012.7.20