Pigeon gaining thrust in flapping up run by back drive of primaries

　A pigeon generates the thrust not only in the flapping down run but also in the flapping up run by the back drive of the primaries. It is characterized by bending of the wing corner and the subsequent drive action with a snap at the primaries. The flapping noise of the columba livia, the wildized pigion, may relate with the appearance/disappearance of the cascade in the primaries caused by the back drive. (Prod. Dec. 2000, full-scale, No.1)