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

旁白：听一个生物课的讲座。

Professor: Now usually when we talk about birds flying long distances, we're discussing seasonal migration.

教授：现在通常当我们谈论鸟类长距离飞行的时候，我们讨论的就是季节性迁徙。

But there's some species that fly long distances not as part of a migration but as part of their regular foraging for food.

但也有一些物种飞跃长距离不是迁徙的一部分，而是常规觅食的一部分。

A great example is the albatross.

一个很好的例子就是信天翁。

Albatross are seabirds that nest on islands and forage for food out in the open sea.

信天翁的在岛上筑巢的海鸟，在开阔的海上觅食。

And you have one species that forages an average of a thousand miles from its nest.

有一种从巢穴平均飞出1000英里去觅食。

And I read in another study where one albatross left a chick in its nest and went out in search of food.

我在另一个研究中读到，信天翁留雏鸟在巢穴里，自己出去觅食。

And by the time it got back to the nest, it has flown nine thousand miles. Yes, Bob?

当它返回巢穴的时候，已经飞了9000英里。是的，鲍勃？

Student: But why don't they just build their nest closer to their food supply?

学生：但是为什么不把它们的巢建在更靠近食物供给的地方呢？

I mean, for one thing, they must burn up a lot of energy flying back and forth and also the parents are gonna have to be away from the nest that much.

我的意思是，一方面，它们来回飞得消耗大量的能量，而且父母不得不离开巢穴那么长的时间。

Aren't the chicks gonna be pretty hungry most of the time?

难道小鸟不会在大部分时间里非常饿吗？

Professor: Ok, good question.

教授：好，好问题。

The chicks are capable of going for long periods of time without food,

小鸟能够长时间不吃东西，

which works out nicely since as you point out, they may not get to eat that often.

因为正如你指出的，它们可能不经常吃到东西。

As far as the parents go, well, first, they typically can't get enough food in a single location.

就父母而言，首先，它们通常不能从一个地方获得足够的食物。

So they have to visit several places on the same foraging trip.

所以它们必须在一次觅食中去好几个地方。

And the locations of good foraging grounds tend to be very far apart.

而好的觅食地点通常相距很远。

And second, they can't always nest on an island that's closest to the best feeding ground because some of those islands have too many predators on them.

其次，它们不能在距离最好的觅食地近的岛筑巢，因为其中一些岛上有太多捕食者。

Predators that would just love some little chicks to snack on.

捕食者很喜欢捕食这些小鸟。

So I don't think they have much choice.

所以我不认为它们有很多选择。

But it still works out because albatross fly using a technique called dynamic soaring,

但是这些问题仍然解决得了，因为信天翁飞行用的技术叫动力滑翔，

which enables them to cover very long distances while expending very little energy.

能够使它们飞跃非常长的距离，然而只消耗非常少的能量。

If it weren't for that, you'd be right.

如果不是这样的话，你说的就会是对的。

They would probably burn up all their energy just flying back and forth.

它们可能仅仅来回飞就消耗了所有的能量。

Another factor is albatross lay only one egg at a time.

另一个因素是信天翁每次只下一个蛋。

So when the parent returns with the food that one chick doesn't have to share it with a lot of other chicks.Yes, Nancy?

所以当父母带着食物返回的时候，那一只小鸟不需要和其它小鸟分享食物。是的，南希？

Student: So you're saying that they might easily fly a thousand miles over the open ocean when they're looking for food?

学生：所以你是说当它们寻找食物的时候，它们可能很容易地在开阔的海域飞1000英里？

Professor: That's right.

教授：没错。

Student: Then how do they know how to get to the food?

学生：那么它们怎么知道如何获得食物？

I mean, which direction to take to get to the food and how do they find their way back home?

我的意思是，去哪个方向获取食物，以及怎么找到回家的路？

Professor: Good point. And the truth is we are not sure. It's very difficult to keep seabirds in captivity where you can study them.

教授：问得好。事实是我们不确定（它们是怎么做到的）。很难将海鸟囚禁起来研究，

And it's very difficult to study them in the wild, you know.

也很难在野外研究它们。

But we think that a lot of what we've learnt about songbirds probably applies to seabirds as well.

但我们认为，很多我们研究到的关于鸣禽的知识也可能适用于海鸟。

So we're thinking that albatross could make use of two different kinds of compasses if you will, a magnetic compass and a celestial compass.

所以我们认为信天翁可能利用了两种不同的指南针（如果你愿意这么称呼的话），磁罗盘和天文罗盘。

The magnetic compass somehow makes use of Earth's magnetic field, much the way a standard compass does.

磁罗盘在某种程度上利用的是地球磁场，差不多像标准罗盘仪那样。

But to prove this, we would have to find some kind of magnetic sensory organ in birds. And we are not sure that we have.

但为了证明这点，我们得在鸟的器官里找到某种磁场感应器官。我们不确定我们是否找到了。

We have found in birds a mineral called magnetite, which we think might be somehow related to this, because magnetite is a natural magnet.

我们在鸟身上找到了一种矿物质，叫磁铁矿，我们认为可能和这个有关系，因为磁铁矿是一种天然磁石。

But the problem is that we've also found magnetite in non-migratory birds, which suggests that it may in fact serve a completely different function,

但问题是，我们在不迁徙的鸟身上也找到了磁铁矿，这表明它可能实际上提供一个完全不同的功能，

not related to navigation at all.

和导航一点关系都没有。

Um, and the other compass, the celestial compass makes use of the stars, more or less the same way humans have historically used the stars to navigate in the open sea.

另一个指南针，天文罗盘利用星星，或多或少和人类历史上用星星航海差不多。

So that's the way we think albatross navigate.

所以这就是我们认为信天翁导航的方式。

So anyway, you know, think about it, how about if you had to go a thousand miles every time you wanted to get a bite to eat?

所以不管怎么说，大家想想看，要是你们不得不每次走上1000英里，就是为吃点东西呢？

Student: Yeah, and we complain about having to walk all the way across campus to get to the cafeteria.

学生：是的，我们连不得不穿越校园去食堂都会抱怨。

Professor: Yeah.

教授：是的。