Intermittent Gliding in the Hunting Flight of the Kestrel, Falco Tinnunculus

The hunting flight of the kestrel (Falco tinnunculus) consists of short bouts of flight at wind speed against the wind with the eyes in a fixed position relative to the ground, and of short flights from one such position to the next. High speed films taken with a camera in a fixed position of a hunting kestrel of known weight and dimensions, allow estimates to be made of the amount of energy required for this behaviour. A theoretical model shows how a bird could economise by alternating flapping flight with short gliding bouts, without changing the position of the eyes above the ground, by mere displacement of the centre of gravity relative to the head. High speed film data confirm predictions from this model.

J. J. Videler, D. Weihs and S. Daan, J. exp. Biol. 102, 1-12, 1983