If you were to see a bird knocking his wings together a hundred times a second, you would expect to hear something that is going snap, knock, knock, knock, knock at the same rate, but instead what you hear is a continuous hum. There’s an interesting relationship between the speed that we see the feathers knocking and the sound that we hear, and that is the sound that we hear is exactly fourteen times the rate of the knocking that we see. If you took one bird and recorded him and measured exactly the pitch of the sound he was making there would be 1500 cycles a second and if you measured exactly the rate he was knocking his wings together, it would be one hundred and seven point and some decimal point, but if you see the relationship between those two numbers it’s 14, and it’s not 15 and it’s not 13 and it’s not 14.532, it is exactly 14, [107 x 14 = 1498] which leads me to believe that every time we’re seeing a knock, something else must be happening 14 times in between every one of those knocks and that’s what’s creating the sound.

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If the sound generated by the Club-winged Manakin is coming from one wing tip hitting the other, we might expect to hear a series of quick knock-like noises. Instead, we hear a continuous hum. Kim Bostwick found that to make the sound we hear the air is actually vibrating 14 times faster than the wing-knocking that occurs 107 times each second. This must mean that for each time the Club-winged Manakin’s wings come together and spread back apart, something else is happening 14 times. What could be happening? Where could these 14 vibrations be coming from?