Taking images of the wilson's snipe when it is doing its courtship flight with the winnowing sound is quite challenging. This is a large crop from a shot I took this morning. It shows clearly how this "instrumental": sound is made. When the snipe goes into the power dive, the four outer tail-feathers are spread and the wind flowing alongside its body in this fast dive makes these stif feathers vibrate, creating the sound we hear which is called winnowing.
Often the sound is only heard with the maker being a tiny speck high in the sky.
J.Poole wetland area.