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1 .<-NARRATOR:->Listen to part of a lecture in a biology class. The class has been learning about birds.
1 .<-FEMALE PROFESSOR:->OK, today we are going to continue our discussion of the parenting behaviors of birds.
2 .And we are going to start by talking about what are known as "distraction displays".
3 .Now if you are a bird, and there was a predator around, what are you going to do?
4 .Well, for one thing, you are going to try to attract as little attention as possible, right?
5 .Because if the predator doesn't know you are there, it's not going to try to eat you.
6 .But sometimes, certain species of birds do the exact opposite.
7 .When the predator approaches, they do their best to attract the attention of that predator.
8 .[not a question]Now why would they do that?
9 .Well, they do that to draw the predator away from their nests, away from their eggs or their young birds.
10 .And the behaviours that the birds engage in to distract predators are called "distraction displays".
11 .And there are a number of different kinds of distraction displays.
12 .Most of the time, when birds are engaging in distraction displays, they are going to be pretending…either that they have injury…or that they are ill…or that they are exhausted…
13 .You know something that will make the predator think, “Oh, here’s an easy meal.”
14 .One pretty common distraction display is what's called the "broken-wing display".
15 .And in a broken-wing display, the bird spreads and drags a wing or its tail, and while it does that, it slowly moves away from the nests, so it really looks like a bird with a broken wing.
16 .And these "broken-wing displays" can be pretty convincing.
1 .Another version of this kind of "distraction display" is where the birds create the impression of a mouse or some other small animals that's running around the ground.
2 .A good example of that kind of display is created by a bird called "the purple sandpiper".
这种行为的一个很好的例子是由一种叫做紫矶鹞（purple sand piper）的鸟类演绎的。
3 .Now what the purple sandpiper does is when a predator approaches, it drags its wings,
4 .but not to give it the impression that its wings is broken,
5 .but to create the illusion that it has a second pair of legs.
6 .And then it raises its feathers, so it looks like it's got a coat of fur.
7 .And then it runs along the ground swirling left and right, you know like it's running around little rocks and sticks.And as it goes along it makes a little squealing noises.
8 .So from a distance it really looks and sounds like a little animal running along the ground trying to get away.
9 .Again, to the predator, it looks like an easy meal.
10 .Now, what's interesting is that birds have different levels of performance of these distraction displays.They don't give their top performance, their prime time performance every time.
11 .What they do is, they save their best performances, their most conspicuous and most risky displays, for the time just before the baby birds become able to take care of themselves.
12 .And they time it that way because that's when they'll have made the greatest investment in parenting their young.
13 .So they’re not going to put on their best performance just after they’ve laid their eggs, because they haven’t invested that much time or energy in parenting yet.
14 .The top performances are going to come later.
15 .Now you have some birds that are quite mature, quite capable, almost as soon as they hatch. In that case, the parent will put on the most conspicuous distraction displays just before the babies hatch.
16 .Because once the babies are hatched, they can pretty much take care of themselves.
17 .And then you have other birds that are helpless when they hatch.
18 .In that case, the parent will save its best performances until just before the babies get their feathers.