英语听力：2013-07-19 《恐龙的战争》3 顽强防御—15

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If you look at various species of plant eaters, they live together in groups, and if one of them spots a predator², they can whinny or hoot³ and let the rest of the herd⁴ know, so that they can keep on alert, or if the predators⁵ are right there, they can all break out into a run and run away from the attacker.

 

Parasaurolophus’ ability to communicate complex messages is a tremendous defensive⁶ advantage. Using its sensitive hearing, these creatures can detect a predator far off in the distance. They send out an alarm call to warn the herd. And even more effective, low-frequency sounds, with their long wavelengths⁷, travel much further than higher frequencies. 

 

These are kinds of sounds that can be transmitted over very long distances. 

 

This extremely low-frequency sound is called infrasound and can travel for kilometers.

 

You can produce a noise so low and so deep not only it goes through the air, it goes through the rocks and through the soil, and you pick it up in your feet. Elephants do that. Rhinos⁸ do that. Hippos do that. Crocodiles do that. Alligators⁹ do that. They produce infrasound. 

 

But for a Parasaurolophus, these calls can be used for more than just communication. Low-frequency infrasound can put up an aggressive form of defense¹⁰. 

 

Infrasound is a weapon. You can scramble¹¹ the brains of your enemy with a blast of infrasound. If you have 100 duckbills, 1,000 duckbills facing the same direction, producing high-decibel sounds, that’s a wave of energy that could knock over a predator or at least discombobulate it…

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