Bird flight and optimal migration.

The development of the mechanical and aerodynamical theory of bird flight has greatly stimulated research at widely different levels in the field of bird movement. Recent work has shown that the drag of bird bodies is less than was previously assumed. Furthermore, the structure and circulation of wingtip vortices in the wake of flying birds have been revealed, with implications for estimating flight performance on the basis of vortex theory. Predictions about optimal speed and flight behaviour have been successfully tested by field studies using optical and radar registration. Flight theory also allows predictions about optimal fuel deposition rules for migrating birds. Research about bird flight, with the dynamic interplay between theoretical development and empirical work in biophysics, physiology and ecology, represents a fine example of a highly successful use of the optimality approach in biology.