生命的进化（1979）

最好是一直到等早上
So the Straits of Gibraltar each spring and autumn
因此直布罗陀海峡的每个春季和秋季
are visited by thousands of bird travellers on their way to or from Africa.
都有成千的鸟类旅行者经过， 要么去非洲，要么从非洲回来
The nearby mountains and the rock itself, warming in the Mediterranean sun,
附近的山和岩石，被地中海的太阳烤热了
produce particularly strong upcurrents of air,
在空气中产生特别强的上升气流
and Africa lies only a few kilometres away across the strait.
穿过海峡，离非洲就只有几公里远了
A kestrel, taking a rest on its long journey.
一只鹰，正在它长长的旅行中休息
Honey buzzards from much of Europe congregate here and share the thermals.
从欧洲来的蜂鹰聚集在这儿， 享受这种上升气流
These great invasions of tourists infuriate the local residents.
这些大型的入侵者激怒了当地的原有者
Sometimes, on dull days, the short-toed eagles can't get the lift they need
有时，在天气阴暗的日子里， 这些短趾雕不能达到它们想要的高度
for launching off to Africa and fly around Gibraltar harbour.
为了飞向非洲，它们在直布罗陀海峡附近盘旋
The local gulls don't care for such intrusion and mob them.
当地的海鸥并不担心那些入侵者， 并且成群滋扰它们
Sometimes they drive them down into the water.
有时，把它们赶往水里
Just another hazard in the risky business of migration.
仅仅是危险的迁徙过程中的另一项危险
A black kite on its way back to Africa after breeding in Europe.
在欧洲出生之后回到非洲的路是艰难的
September in Gibraltar is a marvellous place for the birdwatcher
九月的直布罗陀对鸟类观察家来说 是一个神奇的地方
as travellers congregate at this international crossroads of migration routes.
对迁徙者来说这儿是一个国际的十字路口， 旅行者都聚集在这儿
One of the best places to watch is from the top of the rock.
观察鸟的最好的地方是暗礁的顶端
It's coming to the end of the day and it's been a good one for the migrants.
到最后一天，对迁徙者来说已经是最好的了
Parties of big birds, 30, 40, 50-strong, have been passing the rock
一群大型鸟，30只，40只也许有50只， 刚刚飞过暗礁
and gathering to get one last lift from a thermal in Europe
集中在一起， 从欧洲的上升气流中最后一次升高
so they can gain altitude and glide across the straits to Africa, 12 miles away.
因此它们能够获得更高的海拔， 穿越海峡到达12英里远的非洲
But how did they find their way here?
但是它们在这是怎么找到路的呢？
Some undoubtedly used geographical landmarks.
毫无疑问，一些利用地理界标
They come along the coast.
它们沿着海岸
Others follow prominent river valleys.
其他的随着显眼的河谷
But that can't be all there is to it,
但是并不是所有都这样
because young birds that have never made the journey can do so by themselves.
因为那些从来没有进行过旅行的幼鸟 必须靠它们自己
So they must have some kind of inherited map in their minds.
因此，在它们的脑子里一定有某种遗传地图
Other birds manage to use the sun in some way
其余的靠太阳指路
because they can cross large expanses of sea and even featureless land.
因为它们要穿越 宽广无垠的大海和一马平川的陆地
But the sun has one drawback as a navigational aid.
作为航行的帮助工具，太阳有一个缺点
It moves, so if you want to find your way by it,
它是移♥动♥的，如果你想通过它找到你的路
you have to know what the time is.
你必须知道时间
So those birds, presumably, must also have a clock in their minds.
可假定这些鸟的脑子里还有一个钟
But in the evening, of course, the sun goes down, it gets dark,
当然，到了晚上太阳下山了，一切变得黑暗
and you may no longer be able to see geographical landmarks.
你再也不能看见那些地理标志
What happens then?
会发生什么事呢？
The answer can be found here in the air traffic control tower at the rock.
我们可以在暗礁上的 空中交通管理塔那儿找到答案
Gibraltar is of great strategic importance in the defence of Western Europe
在西欧的防御中直布罗陀海峡 是一个非常重要的战略要地
and close watch is kept by radar of all aircraft movements around it.
雷达监视着所有周围移♥动♥的飞机
But radar can show up flocks of birds just as it can show up aircraft.
雷达能显示鸟就像显示飞机一样
And in the autumn and spring, the information that can come from these screens
在春季和秋季，这种信息能够在显示屏上出现
about what goes on in the skies at night is spectacular indeed.
事实上晚上的天空是非常壮观的
A few hours of an autumn night can be condensed into a few seconds.
几个小时的一个秋季晚上可以被浓缩到几秒钟
The numbers of birds crossing the straits into Africa
大量的鸟穿过海峡到达非洲
can be estimated from the mass of black dots moving south-west.
从大量向南移♥动♥的黑点估计
On this night, up to 200,000 birds at one time are represented on the screen.
一个晚上，多达二十万的鸟 在同一时间里出现在屏幕上
It's estimated that 5,000 million cross the Mediterranean each autumn.
估计一个秋季就有五计亿的鸟穿越地中海
How do they find their way?
它们怎样找到它们的路的呢？
Well, some birds seem to fly by the stars.
一些鸟利用星星引航
If you release them in a planetarium where artificial stars have been twisted around,
如果你把它们释放到一个天文馆里， 在那里人造星星被扭转了方向
they fly by way of those.
它们沿看星星的方向飞行
Others are sensitive to electromagnetic waves.
一些对电磁波很敏感
It appears that a bird not only has to have a map of the land and a star chart and a clock,
可以看出来，鸟不但有地图、星图和时钟
but also a compass in its mind.
在它们的脑子里还有一个指南针
But the fact remains, there's still a great deal we don't know about bird navigation.
但事实说明，对于鸟类的飞行能力 我们还有很多都是不知道的
Gibraltar is only a halfway stage for most migrants.
对大多数迁徙者来说 直布罗陀海峡只是一个中途的落脚点
Arctic terns hatched in Iceland in July
在冰岛七月孵化出的北极鸥
are here in September,
在九月到达这里
but they still have 10,000km to go before they reach their destination.
但是在它们到达它们的目的地之前， 仍然有一万公里的路
Shearwaters move in a different direction,
海鸥向不同的方向迁徙
migrating east and west between the Mediterranean and the Atlantic.
东到地中海和西到大西洋
They're great travellers.
它们是伟大的旅行者
One returned to its nest in Wales, crossing the Atlantic in 12 days.
回到威尔士的巢穴需要在12天内穿越大西洋
This Arctic tern has now reached the southern tip of South America.
这种北极鸥现在到了南美的最南端
Having left the Arctic at the end of summer, when the sun never set,
当太阳不再升起，它们在夏季未离开北极
it's flying to the Antarctic summer, so it sees more daylight than any other creature.
它们飞往南极度过夏天， 因此它比别的动物看见了更多的白天
The African plains are the target for the storks.
非洲草原是鹳的目的地
By the end of September, they're feeding among game
直到九月末，它们在玩耍中进食
just as they did among dairy cows a few weeks earlier.
就像它们几周前在奶牛群中做的那样
So flight, the birds' supreme achievement,
因此，鸟类的最高成就，飞行
has carried them not only to all parts of the world,
带着它们不仅去世界的任何地方
but has made them into the greatest of all animal travellers.
还使它们成为所有动物中最伟大的旅行者
And yet, most surprisingly, some species have abandoned it.
然而，最令人吃惊的是， 一些种类已经放弃了飞行
The ostrich's ancestors could certainly fly.
鸵鸟的祖先肯定会飞
Its body still retains adaptations for flight.
它的身体仍然保留着适应飞行的特质
A beak instead of heavy teeth and jaws,
喙代替了笨重的牙齿和上下颚
and feathers on its wings that sprout in patterns needed for flight.
翅膀上的羽毛萌发着飞行必需的模式
But now they're used only for display.
但是现在羽毛仅仅被用来炫耀
Since the feathers need no longer support the bird in the air,
既然羽毛不再用于鸟在空中飞行
the hooks on the filaments have disappeared
细丝上的钩也消失了
and the feathers have a soft fluffiness
羽毛长出了柔软的绒毛
that is found to be alluring by other creatures as well as female ostriches.
被认为用于吸引其他动物如雌鸵鸟
But why should the ancestral ostrich have given up flight?
为什么古代的鸵鸟要放弃飞行呢？
Well, flying is a very demanding business.
飞行是非常有必要的
If there are no ferocious predators to drive birds into the air,
如果没有凶猛的食肉动物把鸟赶到空中
it's much easier to remain on the ground.
呆在地上更容易些
That often happens today on islands, and it happened once to the ostriches.
那种情况现在经常发生在孤岛上， 曾经在鸵鸟身上发生过
Ostriches belong to one of the most ancient of the bird families.
鸵鸟属于最古老的鸟类群体之一
When they first appeared, about 50 million years ago,
大约5千万年前，当它们第一次出现时
the dinosaurs and other giant reptiles had only recently vanished,
恐龙和其他大型爬行动物刚刚消失
and the position of ruler of the world was vacant.
地球上的统治者的位置还是空的
It seems that birds like that made a bid for it.
看起来好像那种鸟就为此制定了一个规则
There was one great flightless bird in North America
在北美，有一种大型不会飞的鸟
that had a huge, murderous bill,
有一个巨大的，危险的嘴
that looked as though it could kill any animal around.
看起来好像它能杀死附近任何的动物
And even looking at the ostriches, it's not hard to imagine how dangerous they might be
尽管看起来像鸵鸟，很难想象它有多么危险
if they suddenly acquired a taste for red meat.
如果它们突然闻到肉味儿
They could certainly outrun me, and one kick could knock me over and rip me open.
它们肯定能够追上我， 一踢就能把我踢翻，使我开花
But that bid for supremacy by the birds failed.
但是鸟类那个至高的规则失败了
There was another, unobtrusive, creature around at the time
另一种不起眼的动物生存在同时期
that also had warm blood.
也是温血动物
But it was descended from a different group of reptiles,
它遗传自一个特别的爬行动物种群
and it insulated its body not with feathers but with fur.
它不用羽毛而用毛皮来使它的身体隔热
That was the creature whose descendants were to inherit the earth.
那种动物的后代准备继承地球
That was the first mammal.
那是最早的哺乳动物