Effect of alula on slow turn maneuvers in the Magpie (Pica pica): an aviary experiment

Abstract

Maneuverability of bird flight is expected to be under strong natural selection. Therefore wing shape and fly strategy are adapted for better maneuverability in the species own environment. The alula is an appendage feather that on bird wings leading edge. It is considered to prevent stall on the upper wing surface, and to allow higher angle of attack during flight. In the present study, I observed turning flight of bird, and I examined the effect of alula removal on turning maneuvers in the Magpie. Four magpies were filmed with three synchronized high-speed video-cameras during turns in the L-shape corridor, and their flight was analyzed in three dimensions. Body speed was the highest in the upstroke, suggesting that body speed is partly related to change of inertia. The alula removal affected peak bank angle and mean body speed, but mean radius of turn was not affected by the alula treatment. Evidence was collected for the active abduction of alula at the downstroke of turning flight.