新托福听写训练 第14期（在线收听）

As a way of illustrating our discussion of group behavior of animals. We are going to watch which I think is a fascinating video tape about the eland, one of the two major species antelope in Africa. They live in herds about 200 individuals. But first let's go over some of the general advantages animals get from group association. Probably the most important advantage is defense against predators. Simply being in a large group it decreases the chances that any individuals will would be the victim of predator. Cooperated defense further increases the chances of survival survivor for individuals and species. You will see in the video that when the herds are attacked by the hyenas, the elands deliberately drive their young into the center of tightly patched group, the center being safer than the periphery. The herd act in a way that increases the chances of survival of the offspring. Cooperated defense may even take the form of offense. Some species of small birds will join together in groups to attack predator like owls and hawks. Another advantage to live in the groups is a commonsense notion that many eyes are better than a single pair. It has been demonstrated that large herds detect predators at greater distance than do individuals. Of course there is a downside to live in groups also. But let's watch the video before we get into that.