THE HUMMING BIRDS. 
165 
catchers, distinctly heard when darting through the 
air, at once indicates the nature of its sustenance. 
For this reason they often frequent the borders of 
streams ; and are seen skimming over the surface of 
ponds of water, where a minute insect life is most 
abundant. The bills also of many species are pro- 
vided with seratures, to enable them more certainly 
to secure their prey. The corollas of many large 
tubular flowers are infested by microscopic insects, 
which undoubtedly attract the birds, as well as the 
sweet nectar contained in the cup below; and to ob- 
tain which they are furnished with a tongue formed 
like that of the Woodpeckers, divided into two tubes 
which run throughout its entire length, and is capa- 
ble of being protruded to a considerable distance 
from the point of the beak, thus serving the purpose 
of a pump to draw up the honey from the deep re- 
cesses of the flower, while it is also used to collect 
the insects from the corolla. 
In most species of Humming Birds there is a wide 
difference noticeable in the plumage of the males and 
the females, the latter being rarely if ever clothed 
with the rich metallic hues of the former. In a few 
instances where the coloring of both sexes is plain, 
no difference is apparent. The young birds do not 
generally attain their full livery until the second or 
third year; they make their first appearance in the 
sombre garb of the female, which gradually changes 
with each successive moulting until maturity. 
The structure of the scale-like feathers which 
