8 



destroy the decomposing carcasses of the animals slain by some 

 pestilence. Birds are particularly fitted to perform such services 

 in Nature (1) by their wonderful power of flight, (2) by their 

 remarkable vision, (3) by their great capacity for consuming and 

 assimilating food, and (4) by their propensity to wander. 



Birds excel all other creatures in powers of flight. The arctic 

 tern migrates annually from the arctic regions to the Antarctic 

 Ocean. The tiny ruby-throated hummingbird flies from Hudson 

 Bay to Panama. The semi-annual migrations of birds over the 

 northern hemisphere enable them to explore every part of each 

 continent over which they pass, and to exert a periodic re- 

 pressive influence upon all living creatures on which they feed, 

 -first in their northern homes, next in migration over the 

 temperate zone, and last in the southern lands, where they 

 winter and where they reenforce the numbers of resident birds, 

 most of which migrate little if at all. The highly developed 

 flight-powers of birds enable them to overtake and destroy 

 both winged and wingless creatures amid the foliage of plants, 

 on the surface of the earth, in the air, and even in and under 

 the water into which many birds can readily dive and in which 

 many can both swim and fly. Birds, like insects, can quickly 

 reach from the air all external parts of plants, and they are 

 especially formed and adapted for the pursuit of insects. 



Birds find distant food mainly by their almost telescopic 

 sight. Thus warblers high in air discern others far below en- 

 gaged in the act of feeding, and seeing this they drop from the 

 sky and join the busy throng. Thus, too, the vulture, floating 

 -aloft on level pinions, discovers food in the valley below, and 

 circling downward is seen by others in the distant skies; as 

 they turn to follow him they also are observed by others still, 

 and so the tidings spread until at last a great assemblage of 

 these feathered scavengers concentrates at the fatal spot. 



The muscular power exhibited by birds, their high tempera- 

 ture, the extremely rapid circulation of the blood, and their 

 remarkable activity compel them to eat a tremendous amount 

 of food to repair the constant waste of their tissues. The 

 enormous capacity of birds for assimilating food can be appre- 

 ciated by those only who have studied the subject. When food 

 is plentiful birds gorge themselves. So rapid is the digestion of 



