Official 47 Set 3

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Albatross

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What does the professor mainly discuss?
  • A. Long-distance seasonal migration of seabirds

  • B. Two major ways that seabirds navigate

  • C. A seabird that flies far in search of food

  • D. Reasons why seabirds often live on islands

显示答案 正确答案: C

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

    FEMALE PROFESSOR:Now usually when we talk about birds flying long distances, we're discussing seasonal migration.But there's some species that fly long distances not as part of a migration but as part of their regular foraging for food.A great example is the albatross.

    Albatross are seabirds that nest on islands, and forage for food out in the open sea.And you have one species that forages an average of a thousand miles from its nest.And I read in another study where one albatross left a chick in its nest and went out in search of food, and by the time it got back to the nest, it had flown nine thousand miles. [sees hand raised] Yes, Bob?

    MALE STUDENT:But why don't they just build their nest closer to their food supply?I mean, for one thing, they must burn up a lot of energy flying back and forth, and also, if the parents’re gonna have to be away from the nest that much, aren’t the chicks going to be pretty hungry most of the time?

    FEMALE PROFESSOR:Ok, good question.The chicks are capable of going for long periods of time without food, which works out nicely since, as you point out, they may not get to eat that often.

    As far as the parents go, well, first, they typically can't get enough food in a single location.So they have to visit several places on the same foraging trip, and the locations of good foraging grounds tend to be very far apart.

    Uh 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—predators that would just love some little chicks to snack on.So I don't think they have much choice.

    But it still works out, because albatross fly using a technique called dynamic soaring, which enables them to cover very long distances while expending very little energy.If it weren't for that, you'd be right—they would probably burn up all their energy just flying back and forth.

    Another factor is, albatross lay only one egg at a time, so when the parent returns with the food, that one chick doesn’t have to share it with a lot of other chicks.[seeing hand raised]Yes, Nancy.

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

    FEMALE PROFESSOR:That's right.

    FEMALE STUDENT:Then how do they know how to get to the food—I mean, which direction to take to get to the food—and how do they find their way back home?

    FEMALE 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, and it’s very difficult to study them in the wild, you know.

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

    The magnetic compass somehow makes use of Earth's magnetic field, much the way a standard compass does.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.We have found in birds a mineral called magnetite, which we think might be somehow related to this, because magnetite is a natural magnet.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, not related to navigation at all.

    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.So that's the way we think albatross navigate.

    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?

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

    FEMALE PROFESSOR:Yeah.

  • 旁白:请听生物课上的部分内容。

    教授:通常当我们讨论鸟类远距离飞行时,我们讨论的都是季节性迁徙。但是有一些品种的鸟类飞行长距离不是为了迁徙,而是它们日常寻找食物的一部分。一个绝佳的例子就是信天翁。

    信天翁是在海岛上筑巢,在远海中寻找食物的海鸟。这个品种的鸟会在离它的巢平均几千英里的范围寻找食物。我在另一项研究中读到过,信天翁会把雏鸟留在巢里,然后出去寻找食物,等它回到鸟巢时,它已经飞了九千英里了。Bob,请说?

    学生:但是它们为什么不直接把巢筑在离食物供给更近的地方呢?一来,它们往返飞要消耗很多能量,而且,如果父母们不得不远离巢穴,那么大多数时候,雏鸟们是不是会很饿呢?

    教授:问得好。雏鸟能够很长时间不进食,这非常有用,因为正如你指出的,它们可能没机会那么频繁地进食。

    就父母们而言,首先,它们一般在单一的地点找不到足够的食物。所以它们出去觅一趟食必须去好几个地方,而觅食场所的位置往往相差甚远。

    第二,它们不能总是把巢筑在离最佳的觅食地点最近的岛上,因为有些岛屿上有太多的捕食者——捕食者很喜欢吃小雏鸟。所以我觉得它们没什么选择。

    但这还是可以解决的,因为信天翁会用一种叫做动力翱翔的技巧飞行,这使它们能飞越很长的距离,同时几乎不消耗什么能量。如果没有那个技巧,你可能就是对的,仅仅飞个来回它们可能就会耗尽所有的能量。

    另一个因素是信天翁一次只下一个蛋,所以当父母带着食物回来时,雏鸟不用和很多其他雏鸟分食。Nancy,请说?

    学生:所以你说它们在寻找食物时也许能轻易在空阔的海面飞行上千英里?

    教授:没错。

    学生:那它们怎么知道该如何接近食物呢?我是说,它们怎么知道该飞往哪个方向才能找到食物,还有怎么找到回家的路?

    教授:问得好。事实上我们也不确定。要把海鸟关起来进行研究非常困难,而且在野外研究它们也很困难。

    但是我们认为我们了解的很多关于鸣鸟的知识可能也能用在海鸟身上。所以我们认为信天翁能使用两种不同的罗盘,一种磁罗盘和一种天文罗盘。

    磁罗盘在某种程度上利用了地球的磁场,就像标准罗盘所做的那样。但是为了证明这一点,我们必须找到鸟身上的某种磁感应器官,但我们不确定找到了。我们在鸟身上找到了一种叫做磁铁矿的矿物质,我们认为这也许和磁罗盘有某种联系,因为磁铁矿是一种天然的磁铁。但问题是,我们还在其他非迁徙的鸟类身上找到了磁铁矿,这说明它可能事实上发挥着一种完全不同的功能,和航海一点关系也没有。

    另一个罗盘,天文罗盘利用了星星,多多少少和人类在历史上使用星星在远海上航行的方法一样。所以我们认为这是信天翁导航的方式。

    不管怎样,你们可以想想,如果你们每次想吃点什么时都不得不走几千英里的话,会怎么样?

    学生:是啊,我们连必须一路穿过校园走到餐厅都抱怨个不停。

    教授:是啊。

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    题型分类: 主旨题
    原文定位:
    FEMALE PROFESSOR
    Now usually when we talk about birds flying long distances, we’re discussing seasonal migration. But there’re some species that fly long distances not as part of a migration, but as a part of their regular foraging for food. A great example’s the albatross. 
     

    选项分析:

    教授首先介绍albatross是一种每天要飞行很远去觅食的鸟,然后介绍它们为何飞行那么远的原因,最后探讨它确定方向位置的可能机制,对应选项C:A seabird that flies far in search of food。


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