[00:00.49]Not all sounds made by animals serve as language,
[00:04.74]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.
[00:16.31]To get a full appreciation of what this means we must turn first to some recent human inventions.
[00:23.99]Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back.
[00:31.83]The further off this solid obstruction, the longer time will elapse for the return of the echo.
[00:38.06]A sound made by tapping on the hull of a ship will be reflected from the sea bottom,
[00:44.30]and by measuring the time interval between the taps and the receipt of the echoes, the depth of the sea at that point can be calculated.
[00:53.60]So was born the echo-sounding apparatus, now in general use in ships.
[00:59.79]Every solid object will reflect a sound, varying according to the size and nature of the object.
[01:07.53]A shoal of fish will do this.
[01:09.77]So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.
[01:16.92]With experience, and with improved apparatus,
[01:20.48]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.
[01:31.43]It has been found that certain bats emit squeaks and by receiving the echoes,
[01:37.97]they can locate and steer clear of obstacles -- or locate flying insects on which they feed.
[01:45.41]This echo-location in bats is often compared with radar, the principle of which is similar.
