OFFICIAL11 Why does the professor say this?

[00:00.00]Narrator: Listen to part of a lecture in a biology class. [00:04.18]The class has been learning about birds.
[00:07.14]FEMALE PROFESSOR: Okay. Today we're going to continue our discussion of the parenting behaviors of birds... [00:13.81]And we're going to start by talking about what are known as “distraction displays.”[00:19.02]Now if you’re a bird, and there’s a predator around, [00:22.73]what’re you going to do? [00:24.27]Well, for one thing, you’re going to try to attract as little attention as possible, right?
[00:29.62]Because if the predator doesn't know you’re there, it's not going to try to eat you. [00:34.12]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. [00:44.30]Now why would they do that? [00:46.64]Well, they do that to draw the predator away from their nest, away from their eggs or their young birds. [00:54.18]And the behaviors that birds engage in to distract predators are called “distraction displays.”
[01:01.65]And there are a number of different kinds of distraction displays. [01:05.72]Most of the time, when birds are engaging in distraction displays, they’re 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, “Oh, here’s an easy meal.”[01:22.61]One pretty common distraction display is what’s called the broken-wing display. [01:28.19]And uh, 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 nest. [01:39.96]So it really looks like a bird with a broken wing. [01:43.29]And these broken-wing displays can be pretty convincing.
[01:47.47]Another version of this kind of distraction display is where the bird creates the impression of a mouse or some other small animal that’s running along the ground. [01:58.60]A good example of that kind of display is created by a bird called a “purple sandpiper.”[02:05.04]Now what the purple sandpiper does is, when a predator approaches, it drags its wings–but not to give the impression that its wing's broken– but to create the illusion that it has a second pair of legs…
[02:20.96]And then it raises its feathers, so it looks like it’s got a coat of fur…[02:26.29]and then it runs along the ground, swerving left and right–you know, like it’s running around little rocks and sticks…[02:34.02]and as it, as it goes along, it makes this little squealing noise, [02:38.45]so from a distance it really looks and sounds like a little animal running along the ground, trying to get away. [02:46.06]Again, to the predator, it looks like a nice, easy meal.
[02:50.63]Now what’s interesting is that birds have different levels of performance of these distraction displays. [02:57.76]They don't give their top performance, their prime-time performance, every time. [03:03.41]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. [03:17.49]And they time it that way because that's when they’ll’ve made the greatest investment in parenting their young.
[03:23.91]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. [03:32.98]The top performances are going to come later.[03:36.01]Now you have some birds that are quite mature, quite capable, almost as soon as they hatch. [03:42.80]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 other birds that're helpless when they hatch. [03:58.37]In that case, the parent will save its best performances until just before the babies get their feathers.