Nghe TOEFL

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Listen to part of a lecture in a biology class. The professor is discussing the behavior of prairie dogs. Prairie dogs are social rodents that live in large colonies called towns. One of the most fascinating aspects of their behavior is their vocal communication. Researchers have found that prairie dogs have distinct alarm calls for different types of predators, such as hawks, coyotes, and snakes. For example, when a hawk is spotted, the prairie dog gives a specific call that causes others to dive into their burrows. But a call for a coyote, a ground predator, prompts a different response—prairie dogs stand upright and scan the horizon. Interestingly, these calls are not just simple signals. Studies have shown that prairie dogs can even describe the color, size, and speed of a predator. In one experiment, researchers played back recorded calls, and the prairie dogs reacted appropriately to the description, even when the predator was not present. This suggests a level of cognitive complexity that was once thought to be unique to humans and some primates.