NARRATOR:Listen to part of a lecture in a biology class. The class has been learning about birds.
FEMALE 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 was 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's not going to try to eat you.But sometimes, certain species of birds do the exact opposite.When the predator approaches, they do their best to attract the attention of that predator.[not a question]Now why would they do that?Well, they do that to draw the predator away from their nests, away from their eggs or their young birds.And the behaviours 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 injury…or that they are ill…or that they are exhausted…You know something that will make the predator think, “Oh, here’s 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 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.And these "broken-wing displays" can be pretty convincing.
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.A good example of that kind of display is created by a bird called "the purple sandpiper".Now what the purple sandpiper does is when a predator approaches, it drags its wings, but not to give it the impression that its wings 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 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.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’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.The top performances are going to come later.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.Because once the babies are hatched, they can pretty much take care of themselves.And then you have other 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.
另外一种版本的分散注意力，是鸟类制造了一种假象，好像有老鼠等小动物正在周围。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。当一个捕食者在周围时，紫矶鹞做的是，拖拽着翅膀但并不是要假装翅膀断了而是为了制造一种（翅膀下面）有另外一双脚的错觉。然后它竖起羽毛，看起来好像有一层皮毛。然后它沿着地面左右旋转，你知道就像它绕着小石头和树枝跑。当它前进的时候会发出一些吱吱的声音。所以从远处看，的确很像是一个小动物在地上逃跑的样子。同样，这会让捕食者觉得，这是一顿能轻易得手的晚饭。有趣的是鸟类对这些分散注意力的表现有不同程度的表现。它们并不是每次都拿出它们最高超的的手段示人。它们在风险达到顶峰的时刻才会使用最厉害的方法，而当幼鸟即将出巢并且有了自理能力的时候，它们所使用的分散注意力的手段就会是（比较粗糙，甚至有点）冒险的。因为保护幼鸟需要合理地投入精力。所以当鸟类刚下蛋后，它们不会花太多精力做分散注意力的行为，因为它们还有花费更多的精力去哺育幼鸟。高招要稍后再出。而现在，一些幼鸟已经长的比较成熟了，也将在被孵育出的一刻能够自理，这种情况下，它们的父母将上演最显眼的分散精力术，在幼鸟即将破壳之前。因为一旦它们破壳而出，就可以照顾自己了。还有其他的鸟在孵化的时候是无助的。这样，父母就会将最好的分散注意力术一直上演到幼鸟长出羽毛。