The primary feathers are twisted for only a split second, but their twisting is what gives the propeller motion. In an airplane propeller, rotation is around a single point. In a bird wing which oscillates up and down, the feathers must continually change position to produce the thrust. In leisurely flight the wingtip movement is more vertical. The secondary feathers on the inner part of the wing, attached to the ulna, provide lift.
Birds stay aloft by riding rising air currents.
Obstruction currents are updrafts caused by the deflection of a horizontal wind upward by a cliff, hillside, ocean wave, etc. Over the ocean, when the breezes are under 14kph in the fall, the water, being warmer than the air, produces vertical currents of rising warm air on which the birds ride and they soar around in circles. As the wind exceeds 14kph, these vertical columns of air are blown horizontal and birds soar in a straight line. They will soar into the wind to gain altitude and then lose altitude to gain distance. The power for control of the wings comes from the pectoralis muscle which originates on the ventral part of the chest and collar bone and inserts on the ventral side of the arm.