原文已被隐藏，你可用 快捷键 - 或点击 显示原文 按钮来查看原文
第1段
1 .Listen to part of a lecture in a biology class.
该句暂无译文！
2 .(professor) All right, any questions before we move on? Harry?
该句暂无译文！
3 .(male student) I saw this down at the beach and you know, sometimes hundreds of birds fly together in a large flock, and as they fly, all of these birds twist and turn and seem to move at the exact same time. It looks like the flock is one giant organism.
该句暂无译文！
4 .(professor) Spectacular, isn\'t it? We call that behavior coordinated group flight, and it takes many forms.
该句暂无译文！
5 .Sometimes it has a basis in aerodynamics. Um, for example, some bird species fly single file, one following the other; other species fly in V-formations. We think this has to do with aerodynamics.
该句暂无译文！
6 .Birds that fly single file create slip streams, you know, areas of decreased air resistance for the individuals behind them. While birds flying in a V-formation, take advantage of the rising currents of air from the wing tips of their neighbors.
该句暂无译文！
7 .(male student) But not all birds fly in a V-formation or in single file?
该句暂无译文！
8 .(professor) Right! Like the birds you saw at the beach. That\'s why researchers have traditionally accepted what\'s called the safety hypothesis.
该句暂无译文！
9 .You see with all the twist and turns you observed in their flight pattern. Birds can confuse predators quite a bit. So, predators won\'t attack.
该句暂无译文！
10 .One researcher observed that birds were most likely to be attacked when flying alone or in very small flocks.
该句暂无译文！
11 .Actually, surprisingly, she also found that they were likely to be attacked when in very large flocks.
该句暂无译文！
12 .(female student) When you say large flocks, do you mean like 100?
该句暂无译文！
13 .(professor) I\'m talking flocks with more than 500 birds. When in very large flocks, the birds might actually confuse each other instead of confusing the predator.
该句暂无译文！
14 .Anyway, this still supports the safety theory, because if the flocks contain an optimum number of birds, let\'s say, below 500, but more than just a few, predators are less successful in their attacks.
该句暂无译文！
15 .(female student) So, the safety hypothesis seems to make sense?
该句暂无译文！
16 .(professor) Well, yes. But the safety hypothesis can\'t explain everything.
该句暂无译文！
17 .Take starlings for example, it\'s common to see large flocks of these birds flying around above their roosting sites at night. Often for more than half an hour before landing.
该句暂无译文！
18 .(female student) Wow, that\'s like telling their predators here we are when they could have just landed and been safe.
该句暂无译文！
19 .(professor) Exactly. One proposed explanation for this is that maybe there are what we call bird leaders.
该句暂无译文！
20 .And maybe these other birds are just mindlessly following or imitating the leaders. Not for any particular reason as in the aerodynamic hypothesis, but maybe for no reason at all.
该句暂无译文！
21 .But remember, the birds at the front of the flock at one point, those that might be considered leaders can easily be at the back of the flock at another point.
该句暂无译文！
22 .(male student) So, you\'re saying that there really aren\'t any leaders of any kind?
该句暂无译文！
23 .(professor) Not during coordinated group flight.
该句暂无译文！
24 .(male student) Well, what if maybe birds are just programmed for coordinated group flight? You know, maybe it\'s all instinctual.
该句暂无译文！
25 .(professor) That\'s actually been suggested as a hypothesis. It\'s an interesting one.
该句暂无译文！
26 .Several computer programs have been designed to mimic flocks of flying birds with each individual computerized bird program to follow a few simple behavioral rules.
该句暂无译文！
27 .For example, maintaining enough distance to avoid colliding with other birds and attempting to fly the same speed in the direction of other birds.
该句暂无译文！
28 .And the results, well, one of these computer programs produce something so close to actual coordinated group flight. It was used in a Hollywood movie to create digital flocks.
该句暂无译文！
29 .But keep in mind that just because these computer simulations look like coordinated group flight, we can\'t say that real birds follow the rules that computerized birds do. We can\'t even say whether they follow any rules for sure.
该句暂无译文！
30 .Anyway, research continues. And what\'s so exciting is that we\'ve now got people from different fields, not just biology, studying coordinated group flight.
该句暂无译文！
31 .This is important because it\'s such a complex phenomenon that we need researchers with different kinds of expertise to approach things from different angles.
该句暂无译文！
32 .Um. For example, a group of physicists have been looking at bird flight as a statistical problem. Using special equipment, they filmed starlings in Rome and then statistically analyzed each bird\'s movements.
该句暂无译文！
33 .They found that when a bird changes direction, that affects the 6 or 7 birds closest to it, these 6 or 7 birds change direction, which affects more birds and so on.
该句暂无译文！