托福TPO11 Lecture1

TPO11 Lecture 1 Biology Narrator Listen to part of a lecture in a Biology Class. The class has been learning about birds. Professor Ok, today we are going to continue our discussion of the parenting behaviors of birds. And we are going to start by talking about what are known as distraction displays. Now if you are a bird and there is a predator around. What are you going to do? Well, for one thing you are going to try to attract as little attention as possible, right? Because if the predator doesn’t know you are there, it is not going to try to eat you. But sometimes certain species of birds do the exact opposite. When a predator approaches, they do their best to attract the attention of that predator. Now why would they do that? Well, they do that to draw the predator away from their nest, away from their eggs or their young birds. And the behaviors that the birds engage in to distract predators are called distraction displays. And there are a number of different kinds of distraction displays. Most of the time, when birds are engaging in distraction displays, they are going to be pretending either that they have an injury or that they’re ill or that they’re exhausted. You know something that’ll make the predator think: Ah… here is an easy meal. One pretty common distraction display is what’s called the broken-wing display. And in a broken-wing display, the bird spreads and drags a wings 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. And these broken-wing displays can be pretty convincing. Another version of this kind of distraction display is where the bird creates the impression of a mouse or some other small animals that’s running along the ground. A good example of that kind of display is created by a bird called the purple sandpiper. Now what’s the purple sandpiper does is when a predator approaches, it drags its wings but not to give the impression that its wing is broken but to create the illusion that it has a second pair of legs. And then it raises its feathers, so it looks like it’s got a coat of fur. And then it runs along the ground swerving left and right, you know like it’s running around little rocks and sticks. And as it goes along, it makes this little squealing noise. So from a distance it really looks and sounds like a little animal running along the ground trying to get away. Again to the predator, it looks like an easy meal. 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. 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. And they time it that way because that’s when they’ll have made the greatest investment in parenting their young. So they are not going to put on their best performance just after they laid their eggs, because they haven’t invested that much time or energy in parenting yet. The top performances are going to come later. Now you have some birds that are quiet mature, are 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, because once the babies are hatched, they can pretty much take care of themselves. And then you have others birds that are helpless when they hatch. In that case, the parent will save its best performances until just before the babies get their feathers.