 Whales emit two distinct kinds of acoustic signals , which are called whistles and clicks : Clicks are quick broadband burst pulses , used for sonar , although some lower @-@ frequency broadband vocalizations may serve a non @-@ echolocative purpose such as communication ; for example , the pulsed calls of belugas . Pulses in a click train are emitted at intervals of ~ 35 – 50 milliseconds , and in general these inter @-@ click intervals are slightly greater than the round @-@ trip time of sound to the target . Whistles are narrow @-@ band frequency modulated ( FM ) signals , used for communicative purposes , such as contact calls . 
