Hovering of tree sparrow

　For the hovering the sparrow takes the standing pose and flap down its wing from backward up to forward down, and then the air current is produced to forward down. Subsequently the sparrow flap up its wing as if folding and drive back strongly in the midst of the run. Then the feathers of the primaries separate each other and put on inside out and they produce the current to backward down. On average there appears the downward current of the momentum against the gravity. We can say that it makes use of both the lift and the drag on wing (at the angle of attack at which their resultant force inclines to backside) and of the lift on the separated turned feathers. In such a hovering the center of pressure might deviate from the center of gravity, but the sparrow may adjust its pose by using the spread tail.
(Prod. Oct. 2002, full‐scale, No.2)