BIRDS OF THE AIR. 339 
CHAPTER IX. 
BIRDS OF THE AIR. 
There are no birds that so well deserve the designation 
“fowls of the air” as those that, get their subsistence by pur- 
suing flying insects. Eagles and Vultures, Frigate Birds, 
Albatrosses, and some other sea birds, are endowed with 
great powers of flight, but all must descend to earth or 
water for their food ; but Swallows, Swifts, and Nighthawks 
win their sustenance from the air. They may be said to 
live in the air, as, with few exceptions, they seldom alight 
except to rest or to attend to their domestic affairs. 
Unfortunately, the precise character of the food that many 
of these insect-eating birds procure high in air is not well 
known. We see the Swifts and Swallows darting about at 
great heights on clear summer days. We know that they 
must be catching flying insects ; but what insects are flying 
at such a height, and why? They must be winged imagoes. 
Have they finished the business of life, and are they then 
sporting for a few brief hours in sunlight before death over- 
takes them? Are they migrating on the wings of the wind 
to fresh fields? Are they useful, or injurious, insects? No 
one knows. 
When Swallows or Swifts are flying low their food can be 
studied, and we have some definite information regarding its 
character at such times. They are known to take many 
parasitic Hymenoptera, but whether these insects are taken 
before or after they have propagated, whether most of them 
are mainly beneficial, or injurious, parasites, we have little 
information. Therefore, the effect produced by this habit 
of these birds is not well understood. We know, however, 
that many injurious insects, such as flies, gnats, mosquitoes, 
moths, beetles, and plant lice, when about to reproduce their 
kind, are captured by these feathered skimmers of the air. 
We know that the Swallows pursue insects all day, until the 
