There is an urban myth that a duck’s quack does not have an echo. The truth is that it has.
A British study debunked this urban myth. The tests in the study showed that a duck’s quack definitely echoes, just like any other sound, but perhaps not as noticeably. A duck quacks rather quietly, thus the sound coming back is at a low level and might not be immediately heard. A quack is also a fading sound. It has a gradual decay, thus it is hard to tell the difference between the actual quack and the echo.
Ducks were also normally found in open-water areas and did not usually go around echoey cliffs, probably fuelling the theory that their quacks don’t produce an echo.