Characteristic flight style
The results (so far) show that the flight manner, both regarding kinematics and wake structure, differs between swifts and other bird species studied before. The swift flies with relatively rigid wings, flexing them very little during the upstroke. This result in a different wake, with more or less constant shedding of vortices into the wake throughout the complete wingbeat, both down and up, which suggests that the change in forces generated is smooth.
The swifts have long slender aft-swept wings and a stream-lined body. Furthermore, the wings have a very short arm section and a very long hand section compared with most other birds. Their feet are short and mostly used for clinging on to vertical surfaces.
Wake model of flapping flight
The simplified cartoon wake of the swift in flapping flight. It consists of a pair of wingtip vortices connected by spanwise vortices shed from the wing. During down stroke vortices of positive (counter-clockwise) circulation is shed and during up stroke vortices of negative (clockwise).
A swift in flight
A swift in flight keeps its head horizontally even during extreme maneuvers.