FLIGHT OF BIRDS. 19 
single file, either in a straight line or in the form of 
the letter V. 
To the student of Ornithology, the flight of birds, 
and the motion of the wings peculiar to the different 
tribes, will form an interesting subject for observa- 
tion. ‘To the practised eye, this is quite a sure indi- 
cation of the class to which the bird belongs. 
By those who are familiar with the easy and unre- 
strained flight of the Eagle, he is at once recognized. 
Now he soars in graceful curves at an immense height, 
as though intent on viewing the whole earth beneath 
him,—then with unmoving wing glides in a horizontal 
course until lost in the deep blue vault of Heaven. 
The motions of the Turkey Vulture are also of a most 
singular and interesting character. These birds may 
often be seen sailing overhead for hours together, 
moving in curves or gently undulating lines, rising 
and falling at pleasure, with but little apparent mo- 
tion of the wings, and sometimes ascending in easy 
circles beyond the reach of vision. 
The Woodpecker describes, in its course through 
the air, a waving line, which is in consequence of 
the wings being alternately closed and expanded at 
intervals during flight. The Sparrows also perform 
a zigzag course, rising and falling first to the one side 
and then to the other. In the Fly-catchers the mo- 
tion of the wings is rapid and steady; sometimes in 
long-continued flight their course is slightly undula- 
ting. The Humming Bird darts with the swiftness 
of an arrow, and the vibrations of its wings are so 
incessant as to render them almost invisible; while 
