A distant motor thud-thud-thuds as if trying to start, then dies away. The noise repeats, and again dies off. I’ve been fooled by this sound, wondering who could be trying to start a 2-cylinder engine in the middle of the woods. This mechanical noise, of course, is really the drumming of a male ruffed grouse.
People once thought that male grouse struck their wings on a hollow log to produce this low whumping, but better observation revealed something far more astonishing. The bird stands bolt upright on a log, leans back on his tail, and fans his wings vigorously – so fast, in fact, that the wings achieve the same speed as the sound waves generated by their passage through the air. This causes the sound waves to “pile up” into a penetrating shock wave, also known as a sonic boom. For a one-and-a-quarter-pound grouse to exert such force takes strength and perseverance. Novice males have been observed going through all the motions and not producing any sound at all. » Continue Reading.