The drumming of the male Ruffed Grouse is one of the most evocative sounds of the North American forest. Familiar as these accelerating burps are to hunters and hikers, the origin of this bizarre sound was long a mystery. It took the advent of wildlife cinematography to solve the riddle. In the spring of 1929, Cornell University’s Arthur A. Allen filmed a drumming Ruffed Grouse. Frame-by-frame analysis showed the bird’s wings were striking nothing but air — hard and fast enough to produce popping sounds that ran together into the whirring drum. Learn more at BirdNote.org.