Introduction

Abstract

Flight in animals includes gliding, or passive, flight without wingstrokes, which costs a minimum of energy, and flapping, or active, flight. Active flight is a very efficient way to transport a unit of mass over a unit of distance, even though it requires extremely high power output (work per unit time). Flying vertebrates can move more quickly than running ones. While the cheetah, which is the fastest of animals, can achieve 18 body lengths per second, a swift can achieve 67, a chaffinch 72, and a starling 80 (Alerstam 1982; Kuethe 1975). This is not far from a jet airplane, which at Mach 3 reaches about 100 lengths per second.