<p style="TEXT-INDENT: 2em;">Dogs bark, cats meow, birds chirp. We're pretty familiar with these forms of communication. But animals use sounds in other ways too. To find a mate, the male ruffed grouse1 stands on a hollow log and beats his wings, making a drumming sound. The hollow log amplifies the sound so that it can be heard for up to a quarter of a mile. Mole rats use a banging sound for the opposite reason. They like to live alone, so they warn other mole rats to stay out of their way by banging their heads on the top of their tunnels. </p><p style="TEXT-INDENT: 2em;"></p><p style="TEXT-INDENT: 2em;">狗儿汪汪，猫咪喵喵，小鸟啾啾，这是我们再熟悉不过的交流方式了。不过动物们的这些声音还别有用处。雄松鸡在求偶的时候总是站在空心的圆木上拍动翅膀，发出击鼓般的声音。空心的木头可以将声音放大，传到周围0.25英里远的地方。而鼹鼠发出砰砰的声音，其目的则刚好相反。因为它们喜欢独居，所以它们通过用头部撞击自己所在的洞穴上方告诫其他鼹鼠走远点。 </p><table cellspacing="0" cellpadding="0" width="300" align="left" border="0"><tbody><tr><td></td></tr><tr><td bgcolor="#999999"></td></tr></tbody></table><p style="TEXT-INDENT: 2em;">Sometimes making the right sound can be a matter of life and death. With some spiders, including the black widow, the male is much smaller than the female. When the male wants to approach a female to mate, he climbs onto her web and then steps carefully to vibrate2 the web in a certain pattern. This vibration tells the female: “I'm not dinner. I'm one of your kind.” </p><p style="TEXT-INDENT: 2em;">有时候能否发出正确的声音是一件事关生死的事情。在某些蜘蛛群里——例如“黑寡妇”蜘蛛——雄蜘蛛的个头要比雌蜘蛛小得多。在雄蜘蛛需要与雌蜘蛛交配的时候，它会爬到雌蜘蛛的网上，小心地踩住，用一种特定的方式晃动蛛网。这样就等于告诉后者：“我不是什么大餐，我是你的同类！” </p><p style="TEXT-INDENT: 2em;"></p><p style="TEXT-INDENT: 2em;">Anyone who has used a dog whistle knows that dogs can hear sounds pitched so high that humans can't hear them. Other animals, such as cats, bats, moles, hedgehogs3, and dolphins, can also hear high-pitched sounds, or ultrasounds4. </p><p style="TEXT-INDENT: 2em;"></p><p style="TEXT-INDENT: 2em;">如果有谁用过狗哨，那他一定知道狗能够听到音调很高的声音，而人却办不到。其他动物如猫、蝙蝠、鼹鼠、刺猬和海豚也能够听到高音调的声音或者是超声波。 </p>