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旁白：请听一段生物课的课堂讲解。

Narrator: Listen to part of a lecture in a Biology class.

教授：好的，今天，我们来讲一种爬行动物，这种食肉动物在过去的七千万年中都没有太大的进化。

Professor: OK. For today, let's look at a reptile, a predator that hasn't evolved much in the last seventy million years.

提到爬行动物就一定会谈到鳄鱼。

No discussion of reptiles would be complete without some mention of crocodiles.

现在我们通常认为鳄鱼是一种孤僻的动物，它们隐藏在沼泽中，令人感觉十分神秘。

Now, we tend to think of crocodiles as, uh, kind of solitary, hiding out in a swamp, uh, kind of mysterious creatures.

但是我们发现鳄鱼并不像大家想象的那样孤僻。

But we are finding out that they aren't as isolated as they seem.

实际上，鳄鱼之间的互动方式多种多样。

In fact, crocodiles interact with each other in a variety of ways.

其中一种就是发声法，也就是动物发出的声音。

One way is with vocalizations, you know, sounds generated by the animal.

整个鳄鱼族类都是如此，包括短吻鳄。

This is true of the whole crocodile family, which includes crocodiles themselves, alligators, etc.

如果在繁殖季的沼泽中，你就会听到各种声音此起彼伏，低沉的咕噜声，嘶嘶声，这些声音都是雄鳄鱼发出的。

If you were to go to a swamp during the breeding season, you'd hear a chorus of sounds, deep grunts, hisses, these are sounds that male alligators make.

而有的声音大到可以引起水的震动。

And some of them are powerful enough to make the water vibrate.

可以向其它雄性发出走开的信号。

This sends a strong, go-away message to the other males.

这样它就可以专注的通过水来发出其它的声波，而由于这种声波的频率很低，我们大家都无法听到。

So the alligator can focus on sending other sound waves through the water, sound waves that you and I couldn't even hear since they are at such low frequency.

但是雌鳄鱼可以接收到这种声音，找到并与雄鳄鱼交配。

But they do reach the female alligator, who then goes to find and mate with the male.

发声法，嗯……也用在其它的原因，比如说引起注意，或者只是嗯……让其它鳄鱼知道它们很忧虑。

Vocalization is um...well, it is used for other reasons, like getting attention or just, um...letting others know you are distressed.

新生的鳄鱼或刚孵出的小鳄鱼与母鳄鱼之间的沟通。

New-born crocodiles, or hatchlings and their interactions with their mothers.

当小鳄鱼刚出生的时候……它们会在巢穴中发出一种压抑的声音。

When they are born, croc... baby crocodiles have a sort of muffled cry while they are in their nest.

刚孵化的小鳄鱼十分脆弱，尤其是面临鸟类和小型的哺乳动物的威胁。

Hatchlings are really vulnerable, especially to birds and small mammals when they are born.

但是它们的妈妈在附近守夜，听到它们的叫声后，就会将它们转移到安全的地方，也就是水中。

But their mother, who has been keeping vigil nearby, hears their cry for help and carries them to safety, meaning, to water.

卵是一起孵化的，所以母鳄鱼要照顾40只刚刚出生的小鳄鱼。

Uh, uh, all the eggs hatched at once, so she has about forty newborns to look after.

她一次可以转移15只，将小鳄鱼放在她的嘴里带到附近的水中。

Well, she takes about fifteen out of the nest at a time, carrying them in her mouth to the nearby water.

当她将第一批新孵化的小鳄鱼送到水里是，其它的小鳄鱼就等待着她回来。

While she is taking one load of hatchlings, the others wait for her to come back.

但是你想它们会安静的等着妈妈回来吗？当然不会。

But do you think they are quiet about it? No way.

它们大叫着引起妈妈的注意，尖叫着就像是说别忘了还有我呢！

They are clamoring for the mother's attention, sort of squeaking and practically saying-don't forget about me!

上个星期我在电视上的一个有关鳄鱼的节目上看到了不少这样的例子。

I heard some great examples of this on the television program on crocodiles last week.

里面有几段非常有意思的画面。

但是你看节目的时候要仔细，抱着审视的态度。

But you know, uh, you have to be careful, think critically.

有时候我真不知道它们是从哪里请的专家。

Sometimes I don't know where these shows find their experts.

那，嗯……它们的叫声总能起到保护它们的作用吗？

But, um... does all that crying defeat the purpose?

我是说，难道它们的叫声不会引起其它食肉动物的注意吗？

I mean, doesn't it attract more predators?

我想如果小鳄鱼引起了母鳄鱼的注意，它们就是安全的。

I guess, well, I am guessing that once the babies have the mother's attention, they are safe.

母鳄鱼不会离开太远的。我想……你会去惹一只母鳄鱼吗？

She's never too far away, and, and I think...I mean, would you mess with a mother crocodile?

当母鳄鱼将小鳄鱼都转移完毕，它们还会继续叫嚷，跟其它的小鳄鱼还有它们的妈妈。

So after the mother transports all the youngsters, they still call to each other, and to their mother.

这种交流一直会持续到它们成年后。

This communication continues right through to adulthood.

鳄鱼能够发出18种不同的声音。

Crocodiles have about eighteen different sounds that they can make.

有低沉的咕噜声，嘶嘶声，咆哮声，还有许多不同的声音来交流或传递信息。

There's...um...um... you have deep grunting sounds, hisses, growls, squeaks,roars, so there are many different sounds to interact or send messages.

相比爬行动物，哺乳动物的声音交流更具代表性。

This is more typical of mammals than of reptiles.

我的意思是，在爬行动物中鳄鱼的大脑是最发达的。

I mean, crocodiles' brains are the most developed of any reptile.

在某种程度上，它们的大脑比其它爬行动物更接近哺乳动物。

In that sense, they are closer to mammals' brains than other reptiles' brains.

而据我们所知，哺乳动物，比如说狗，能发出许多种不同的声音。

And we know that mammals, dogs for example, dogs vocalize many different sounds.

而鳄鱼的发声相对复杂，这使它在爬行动物中十分独特。

Crocodiles have a similar level of, uh, vocal sophistication, if you will, which makes them unique among reptiles.

还有一种情况，如果一只新生的鳄鱼离开了它家族的巢穴，一旦达到一定距离，它的生存本能就会发挥出来，

Another thing would be, um, if a hatchling gets separated from the rest of its family, once the others get far enough away, its survival instinct kicks in.

它会发出很大的悲痛的叫声，如果它的兄弟姐妹听到了就会回应他，

It will make a loud distress call, which its siblings answer.

它们会来回叫直到它们找到对方。

And they continue calling back and forth until they all find each other again.

还有另一种情况，是我提到的电视节目中没有提到的。

Another thing, something that wasn't on that TV show I mentioned.

嗯……当母鳄鱼带领小鳄鱼从一个地方转移到另一个地方，比如说它们要寻找另一处水源。

Um... mother crocodiles lead their young from one area to another, like when they have to find a different source of water.

通常它们会在夜里行动，因为这时相对比较安全。母鳄鱼在前面领路并发出叫声以确认小鳄鱼是否跟着她。

Usually she will lead them at night, when it is safer for them, moving ahead and then letting out calls of reassurance so that they will follow her.

她的声音会鼓励小鳄鱼，让它们得到离开这个区域的勇气，出发去其它更适合它们生存的地方。

Her voice helps give the babies the courage they need to leave the area and go someplace that's a more desirable home for them.

According to the professor, what are two functions of the sounds made by male alligators?

Based on the discussion, what is one reason hatchlings make vocalizations to their mother while they are in the nest?

What is the professor's opinion about the television program that she mentions?

What happens when a hatchling makes a distress call?

Narrator: Listen to part of a lecture in a Biology class. 
Professor: OK. For today, let's look at a reptile, a predator that hasn't evolved much in the last seventy million years. No discussion of reptiles would be complete without some mention of crocodiles. 
Now, we tend to think of crocodiles as, uh, kind of solitary, hiding out in a swamp, uh, kind of mysterious creatures But we are finding out that they aren't as isolated as they seem. In fact, crocodiles interact with each other in a variety of ways. One way is with vocalizations, you know, sounds generated by the animal. This is true of the whole crocodile family, which includes crocodiles themselves, alligators, etc. 
Take American alligators. If you were to go to a swamp during the breeding season, you'd hear a chorus of sounds, deep grunts, hisses, these are sounds that male alligators make. And some of them are powerful enough to make the water vibrate. This sends a strong, go-away message to the other males. So the alligator can focus on sending other sound waves through the water, sound waves that you and I couldn't even hear since they are at such low frequency. But they do reach the female alligator, who then goes to find and mate with the male. 
Vocalization is um...well, it is used for other reasons, like getting attention or just, um... letting others know you are distressed. Let's see. New-born crocodiles, or hatchlings and their interactions with their mothers. When they are born, croc... baby crocodiles have a sort of muffled cry while they are in their nest. Hatchlings are really vulnerable, especially to birds and small mammals when they are born. But their mother, who has been keeping vigil nearby, hears their cry for help and carries them to safety, meaning, to water. 
So she takes them out of the nest. Uh, uh, all the eggs hatched at once, so she has about forty newborns to look after. 
Well, she takes about fifteen out of the nest at a time, carrying them in her mouth to the nearby water. While she is taking one load of hatchlings, the others wait for her to come back. 
But do you think they are quiet about it? No way. They are clamoring for the mother's attention, sort of squeaking and practically saying-don't forget about me! 
I heard some great examples of this on the television program on crocodiles last week. Anyone catched it? It had a few interesting bits. But you know, uh, you have to be careful, think critically. Sometimes I don't know where these shows find their experts. 
Student: Excuse me. But, um... does all that crying defeat the purpose? I mean, doesn't it attract more predators? 
Professor: Hmm...good question. I guess, well, I am guessing that once the babies have the mother's attention, they are safe. She's never too far away, and, and I think...I mean, would you mess with a mother crocodile? 
So after the mother transports all the youngsters, they still call to each other, and to their mother. This communication continues right through to adulthood. Crocodiles have about eighteen different sounds that they can make. 
There's...um...um… you have deep grunting sounds, hisses, growls, are many different sounds to interact or send messages. This is more typical of mammals than of reptiles. I mean, crocodiles' brains are the most developed of any reptile. 
In that sense, they are closer to mammals' brains than other reptiles' brains. And we know that mammals, dogs for example, dogs vocalize many different sounds. Crocodiles have a similar level of, uh, vocal sophistication, if you will, which makes them unique among reptiles. 
Another thing would be, um, if a hatchling gets separated from the rest of its family, once the others get far enough away, its survival instinct kicks in. It will make a loud distress call, which its siblings answer. It calls again. And they continue calling back and forth until they all find each other again. Another thing, something that wasn't on that TV show I mentioned. Um... mother crocodiles lead their young from one area to another, like when they have to find a different source of water. Usually she will lead them at night, when it is safer for them, moving ahead and then letting out calls of reassurance so that they will follow her. Her voice helps give the babies the courage they need to leave the area and go some place that's a more desirable home for them. 
In that sense, they are closer to mammals' brains than other reptiles' brains. And we know that mammals, dogs for example, dogs vocalize many different sounds. Crocodiles have a similar level of, uh, vocal sophistication, if you will, which makes them unique among reptiles. 
Another thing would be, um, if a hatchling gets separated from the rest of its family, once the others get far enough away, its survival instinct kicks in. It will make a loud distress call, which its siblings answer. It calls again. And they continue calling back and forth until they all find each other again. Another thing, something that wasn't on that TV show I mentioned. Um... mother crocodiles lead their young from one area to another, like when they have to find a different source of water. Usually she will lead them at night, when it is safer for them, moving ahead and then letting out calls of reassurance so that they will follow her. Her voice helps give the babies the courage they need to leave the area and go some place that's a more desirable home for them.