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w关键词：bird/鸟，migration/迁移，experiment/实验，magnetic/磁的
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w目录：Culture/文化 |
w话题：鸟类，实验 |
w类型：说明文 |
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w难度级别：
初级 |
w词汇要求：700 |
w文章词数：380 |
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How do the birds
find their way
on these enormously long journeys? |
The
migration of birds
鸟类的迁移
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作者：Unknown |
来源：www.englishfree.com.cn |
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日期：2008-4-1 |
责编：Emma |
Here is a scientific experiment
on the homing of birds. Seven swallows were caught near their
nests at Bremen in Germany. They were marked with a red dye on
some of their white feathers, so that they could easily be seen.
Then they were taken by airplane to Croydon near London; this is
a distance of 400 miles. The seven swallows were set free at
Croydon. Five of them flew back to their nests at Bremen.
How did the birds find their way
on that long journey, which they had never made before? That is
the great puzzle. Perhaps migrating birds are the greatest
mystery of all. Swallows leave England in August and September,
and they fly to Africa, where they stay during the winter season
of England. The swallows return to England in the spring to
nest. There are other birds too that leave England in the late
summer for the south. A lot has been found out about the
journeys of migrating birds by marking the birds with aluminum
rings put on one leg. An address and a number are put on the
ring.
Swallows from England go as far
as South Africa. From England to South Africa is a journey of
6,000 miles. And the birds not only return from Africa to
England next spring, but often they come back to nest in the
very same house where they nested the year before.
How do the birds find their way
on these enormously long journeys? The young birds are not
taught the road by their parents, because often the parents fly
off first. We have no idea how the birds find their way,
particularly as many of them fly by night, when landmarks could
hardly be seen. And other birds migrate over the sea, where
there are no landmarks at all.
It has been
suggested that birds can sense the magnetic lines of force
stretching from the north to south magnetic poles of the earth,
and so direct themselves. In order to test this hypothesis,
magnets were attached to the birds' heads in some experiments to
see whether their direction-sense was confused. It was found
that the birds' direction-sense was indeed confused. Other
experiments also seemed to show that birds can take their
direction from the stars.
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