陳蕙雅思教材 - 雅思閱讀精選 (Animals' Compasses)

Animals' Compasses

Researchers have foundthat migrating animals use a variety of inner

compasses to help themnavigate. Some steer by the position of the Sun.

Others navigate by thestars. Some use the Sun as their guide during the

day and then switch to star navigation by night. One studyshows that the

homing pigeon uses theEarth's magnetic fields as a     guide infinding its

way home and there areindications that various other animals from insects

to mollusks, can      also make use of magnetic compasses. It isof course very

useful for a  migrating bird to be able to switch to a   magnetic compass

when clouds cover theSun; otherwise it would just have to land and wait

for the Sun to comeout    again.

Even with the Sun orstars to steer by, the problems of navigation are more

complicated than theymight seem at       first. For example, aworker honeybee

that has found a richsource of nectar and pollen flies rapidly home to the  

hive to report. Anaturalist has discovered that the bee scout delivers her

report through acomplicated dance in     the hive, inwhich she tells the

other workers not onlyhow far away the food is, but also what direction to

fly in relation to theSun. But the Sun does not stay in one  place all

day.  As  theworkers start  out to gather  the food,         theSun may already

have changed its positionin the sky somewhat. In later trips during the

day, the Sun will seem tomove farther and farther toward the west. Yet the

worker bees seem to haveno trouble at all in finding the food source.

Their inner clocks tellthem just where the Sun will be and they change

their coursecorrespondingly.

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嚮導來找到回家的路。  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

果烏雲遮日，它可以以磁場為嚮導繼續飛行，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複雜得多。

例如，一隻工蜂 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裡跳了一段極為複雜的

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。

當蜂群出發採食時，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。