676 BIRDS, 
directions are combined. The raising of the wing after each stroke 
requires relatively little effort, the resistance to be overcome being 
very slight. In steering, the feathers of the tail often bear to the 
wings a relation comparable to that between rudder and sail. 
Fic. 376.—Wings coming down.—From Marey. 
Modes of flight,—There are three chief modes of flight :-— 
1. By gliding or skimming, during which the bird has its wings 
spread, but does not flap them, depending for its movement on the 
ms 
Fic. 377.— Wings completely depressed.—From Marey. 
velocity acquired by previous strokes, by descending from a higher 
to a lower level, or by the wind. This may be readily observed in 
gull and heron, in a pigeon gliding from its loft to the ground, or in 
a falcon swooping upon its quarry. 
