1986年高中英语(第三册补充阅读6)

Supplementary Reading 6 Mysteries of Migration

Winter weather comes with its extreme coldness and low supply of food. Since most animals can not survive in it, they either sleep through it or migrate.

The urge to migrate is very strong in some birds. Each year the tern can produce offspring only during a two-month period. During those two months the tern lives in the region near the North Pole. In the ten months between this time and the next, he flies all the way from the North Pole to the South Pole, and then back north again. That is a distance of about 22,000 miles. To accomplish this, the tern must fly about 75 miles every day for ten months!

What causes birds to migrate? How do they know when to migrate? How do they find their way on such long trips? And why do they come back from those warm comfortable places?

Studies in New York State show that it is the bird's biological time clock that causes a bird to migrate. A bird specialist kept some birds in a planetarium. He was surprised to find that they didn't pay any attention to the stars in the ceiling when migration time came. But then he gradually gave them periods of false daylight, making the days shorter and shorter, as they are in the fall. Within a few weeks the birds tried their best to fly south. He also found that the birds navigate by the North Star once they get the urge to migrate. In fact, when the North Star was removed from the false sky, the birds became completely confused and flew in all different directions.

Some birds find their way by the position of the sun in the sky. But most birds migrate at night. Apparently they migrate by the stars just as pilots of ships do.

This was shown scientifically by some studies in Germany recently. Native song birds were kept inside a planetarium. In the center of the floor of a planetarium a machine shoots lights on to the ceiling, making small points of light to look like stars. The operator can imitate the night sky over any part of the earth by changing the machine. Inside the building the birds all became excited on the day of their usual migration. They all tried to fly south to Africa to their winter home.

Then the experimenters changed the lights so that the sky on the ceiling was like that in Russia. At once the birds changed direction in the building to face what would have been the direction of Germany if they had been in Russia. When the false "sky" was slowly changed so that it was again like the one over Germany, the birds again turned to face Africa, trying to escape and fly a thousand miles.

If things are so good in the warm climates that birds return there every winter, why do they come back north every spring? The warm region is crowded with birds, and the short winter stay of the migrants puts space and food on short supply. The area also has many turtles, snakes, and other animals that steal from bird nests, so birds return north to lay their eggs.

Bird migration is the most familiar migration. But other animals migrate too. Every fall monarch butterflies all over Canada and the United States take an extremely long migration trip. They start out singly, then join others in crowds, moving in great numbers through the skies. Sometimes the butterflies fly in a single line, and other times they crowd together in thick black clouds, then stop in trees, making the covered branches move as if they were living.

When you hold a butterfly in your hand and see the thin wings, you wonder how the butterflies can make these long trips. But they fly thousands of miles, often ten to forty miles an hour. No one knows how they find their way to the same places in California, Florida, and Mexico — but they do. And, as did their parents and grandparents, they not only go to the same towns for the winter, but sometimes even land in the same trees. In the spring the butterflies leave the trees and return north again. There they lay their eggs on young plants that are just coming up above the ground. After they lay their eggs, they die.

Other creatures migrate too. Clouds of locusts sometimes cover the sky and eat everything visible. Eels leave the streams of Europe and America in the fall and travel as far as 5,000 miles to reach the Sargasso Sea in the Atlantic Ocean near Central America. Green turtles that live in Brazil set out every two or three years and travel across more than a thousand miles of open sea to lay their eggs on tiny islands in the South Atlantic Ocean. Salmon return to their home streams to lay their eggs, as do other fish.

Many other animals migrate, some short distances, some to the other side of the world.

Man, too, has been a great migrator. Many forces have kept man on the move — wars, religions, food, sickness. The most commonly known migrators were the groups who moved with the changes of seasons. These groups followed the animals north in the spring and south in the fall. For example, the American Indian followed the buffalo for centuries.

Man started his life upon the earth moving from one place to another. Moving frequently, looking for food, hunting here, picking fruit there — this was the earliest human way. That urge to move is still in most of us, but it is also balanced with the opposite and newer urge to farm and build cities.

精准翻译

冬天来临，严寒肆虐，食物匮乏。大多数动物无法在这样的环境中生存，于是要么冬眠度过，要么迁徙他方。

某些鸟类的迁徙冲动极为强烈。北极燕鸥每年只有两个月的繁殖期。这两个月里，它生活在北极附近地区。在两次繁殖期之间的十个月里，它从北极一路飞到南极，再飞回北方。全程约两万两千英里。为了完成这一旅程，燕鸥必须在十个月里每天飞行约七十五英里！

是什么促使鸟类迁徙？它们如何知道何时启程？在如此漫长的旅途中，它们靠什么辨别方向？又为什么要从那些温暖舒适的地方返回北方？

纽约州的研究表明，是鸟类的生物钟引发了迁徙。一位鸟类专家把一些鸟养在天文馆里。他惊讶地发现，当迁徙季节来临时，这些鸟对天花板上的星星毫不在意。但当他逐渐给它们人为缩短光照时间，让白天越来越短，就像秋天一样时，几周之内，这些鸟就拼命想往南飞。他还发现，鸟类一旦产生迁徙冲动，就靠北极星导航。事实上，当假天空中的北极星被移走后，鸟儿们完全迷失了方向，四处乱飞。

有些鸟靠太阳在天空中的位置辨别方向。但大多数鸟类在夜间迁徙，显然它们像轮船领航员一样靠星星指路。

最近德国的一些研究科学地证明了这一点。研究人员把本地鸣禽养在天文馆里。天文馆地板中央有一台机器，把光投射到天花板上，形成小星星一样的光点。操作员可以通过调节机器，模拟地球上任何地方的夜空。在馆内，这些鸟在通常迁徙的那天都变得兴奋起来，全都试图向南飞往非洲的越冬地。

随后实验人员改变了灯光，让天花板上的星空变成俄罗斯上空的样子。鸟儿们立刻在馆内改变了方向——如果它们真的在俄罗斯，那就是朝向德国的方向。当假"天空"被缓慢调回德国上空的样子时，鸟儿们又重新转向非洲，试图飞出千里之外。

既然温暖的气候那么好，鸟儿每年冬天都回去，为什么每年春天又要飞回北方呢？因为温暖地区鸟类密集，候鸟短暂的越冬停留让空间和食物都变得紧张。那里还有许多乌龟、蛇和其他动物会偷食鸟巢里的东西，所以鸟儿要飞回北方产卵。

鸟类迁徙是最常见的迁徙现象。但其他动物也会迁徙。每年秋天，加拿大和美国各地的帝王蝶都要进行一段极其漫长的迁徙之旅。它们起初独自出发，随后成群结队，铺天盖地地飞过天空。有时蝴蝶排成单列飞行，有时聚成厚厚的黑云，然后停在树上，让被覆盖的树枝像活了一样晃动。

当你把一只蝴蝶捧在手里，看着它那薄薄的翅膀，不禁会想，蝴蝶怎么能完成如此漫长的旅程。但它们能飞行数千英里，时速常常达到十到四十英里。没人知道它们是如何找到去加利福尼亚、佛罗里达和墨西哥那些相同地方的路——但它们确实做到了。而且，就像它们的父母和祖父母一样，它们不仅冬天去相同的城镇，有时甚至落在同一棵树上。春天，蝴蝶离开树木，再次飞回北方。它们在刚破土而出的幼苗上产卵，产完卵后便死去。

其他生物也会迁徙。蝗群有时遮天蔽日，所到之处寸草不留。鳗鱼在秋天离开欧洲和美洲的河流，跋涉五千英里，到达中美洲附近大西洋中的马尾藻海。生活在巴西的绿海龟每隔两三年出发一次，横渡一千多英里的公海，到大西洋南部的小岛上产卵。鲑鱼和其他鱼类一样，回到自己出生的河流中产卵。

许多其他动物也会迁徙，有的短途，有的则远至地球另一端。

人类同样是伟大的迁徙者。战争、宗教、食物、疾病——诸多因素驱使人类不断迁移。最广为人知的是随季节变化而迁徙的族群，他们春天追随动物北上，秋天又南下。例如，美洲印第安人几个世纪以来都追随着野牛群生活。

人类在地球上的生命始于不断的迁移。频繁迁徙，寻找食物，这里狩猎，那里采摘——这是人类最早的生存方式。这种迁徙的冲动至今仍存在于我们大多数人心中，但它也与另一种相反的、更新的冲动——耕种和建造城市——保持着平衡。

语法简析

1. 强调句型："it is the bird's biological time clock that causes a bird to migrate" 是 It is...that... 强调句型，被强调部分是主语。去掉框架后句子仍完整：The bird's biological time clock causes a bird to migrate.

2. as if 虚拟语气："making the covered branches move as if they were living" 中 as if 引导方式状语从句，用虚拟语气 were，表示"好像活了一样"，与事实不符。

3. as 引导倒装："as did their parents and grandparents" 是 as 引导的倒装结构，did 代替前文的动词 find their way，表示"正如它们的父母和祖父母一样"。

4. 并列省略结构："some short distances, some to the other side of the world" 是独立主格式的并列省略，完整形式为 some migrate short distances, some migrate to the other side of the world，简洁有力。