20 INTRODUCTION. 
the Heron and the Crane wheel their heavy bodies 
through the air with a slow but steady flapping of a 
pair of ample, curving wings, their heads drawn in 
toward the body, and their long legs following like a 
rudder. 
It is very evident that the shape of the wings, and 
the arrangement and texture of the feathers com- 
posing them, must have a material effect upon the 
flight of birds. A long, pointed, flat wing, with stiff 
and close-set primaries, is undoubtedly best adapted 
to rapidity of motion. This will be most observable 
in the Swallow, the Humming Bird, and the Night 
Hawk, which of all birds are the most remarkable 
for the nimbleness and agility of their movements. 
How beautifully does the Swallow skim over the 
meadows and lakes, or mount aloft in the air, now 
wheeling to the one side and then darting like an 
arrow to the other! And how graceful are the antics 
of the Night Hawk as he pitches his aérial summer- 
sets, or gambols with matchless ease across the sky! 
It will be observed that the wings of birds of rapid 
flight are seldom very concave beneath; on the con- 
trary, they are generally quite flat when extended. 
This flatness, although it contributes to the velocity 
of motion as the bird sweeps along, destroys to a 
great extent the power of direct ascent. Where the 
wing is of moderate length and concave, as in the 
Owl, and composed of loose soft feathers, the flight 
is buoyant and noiseless, and quite different from that 
of the Falcon, the feathers being too soft and yield- 
ing to produce any whistling or rushing noise. A 
