Bats
Not all sounds made by animals serve as language, and we have only to turn to that extraordinary discovery of echo-location in bats to see a case in which the voice plays a strictly utilitarian role.
To get a full appreciation of what this means we must first to some recent human inventions. Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back. The further off this solid obstruction, the longer time will elapse for the return of the echo. A sound made by tapping on the hull of a shop will be reflected from the sea bottom, and depth of the sea at that point can be calculated. So was born the echo-sounding apparatus, now in general use in ships. Every solid object will reflect a sound, varying according to the size and nature of the object. A shoal of fish will do this. So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish. With experience, and with improved apparatus, it is now possible not only to locate a shoal but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo.
A few years ago it was found that certain bats emit squeaks and by receiving the echoes they could locate and steer clear of obstacles -- or locate flying insects on which they feed. This echo-location in bats is often compared with radar, the principle of which is similar.
动物发出的声音不都是作为语言的。我们仅将蝙蝠的回声定位这一特殊的发现作为声音作用的一个例子。
要对此做一全面的评价，我们首先来了解一些近来的人类发明。人人都知道如果在墙或者山腰附近呼喊，会听到回声。距离固体障碍物越远，则回声的间隔时间越长。在船体外壳上敲打发出的声音会从海底反射。通过测量敲打与接受回声的间隔时间，这一点的海底深度就可计算出来。这就是现在船只上广泛使用的回声定位仪。所有的固体都会反射声音，并因大小和材质而不同。鱼群也会反射声音。所以相比较测量海底，定位鱼群是类似的步骤。通过经验和改良的设备，现在已经不仅仅能定位鱼群，而且通过回声类型可以了解究竟是鲱鱼、鳕鱼、还是其他已知的鱼类。
几年前，人们发现有些蝙蝠会发出尖叫，通过接收回声，它们可以清楚的避开障碍物，并定位她们捕食的昆虫。这种回声定位经常被比喻成具有类似原理的雷达。
