This video says about itself:
Slow Motion Philippine Eagle Flight
13 July 2016
To understand the unique flight styles of different bird species, scientists use a technique called wing tracing. It involves tracing the trajectory of a point on their wing during a series of wingbeats. The pattern of a bird’s wingbeat depends on how far a bird can move its wing in any given direction, which is determined by the length and shape of the wing. Soaring birds such as this Philippine Eagle, for example, show an elliptical shaped wingtip path when viewed from the side.