of animals takes place and eagles, vultures, crows and other scavengers hasten 

 to tear the flesh from the carcasses. A dead sea monster is cast upon the shore, 

 and sea birds promptly assemble to devour its wasting tissues. The gathering of 

 birds to feed is commonly observed in the flocking of crows in meadows where 

 grasshoppers or grubs abound, the assembling of crows and blackbirds in corn- 

 fields, and in the massing of shore birds on flats or marshes where the receding 

 tide exposes their food. 



A study of the structure and habits of birds shows how well fitted they are 

 to check excessive multiplication of injurious creatures or to remove offensive 

 material. Birds are distinguished from all other animals by their complex 

 feathered wings — the organs of perfect flight. 



Birds are provided with wings to enable them (1) to procure food, (2) to 

 escape their enemies, (3) to migrate. 



Birds are pursued by many enemies. Water fowl fly to the water and dive 

 to escape the hawk or eagle, and fly to land to escape the shark, alligator or pike. 

 Sparrows fly to the thicket to elude the hawk, and to the trees to avoid the cat. 

 Evidently this great power of flight was given birds to enable them not only to 

 concentrate their forces rapidly at a given point, but also to pursue other flying 

 creatures. Birds can pursue bats, flying squirrels, flying fish and insects through 

 the air. Bats and insects are their only competitors in flight. Comparatively 

 few insects can escape birds by flight, and this they do mainly by quick dodging 

 and turning. The speed at which birds can fly on occasion has seldom been 

 accurately measured. The maximum flight velocity of certain wild fowl is said 

 to be ninety miles an hour. Passenger pigeons killed in the neighborhood of 

 New York have had in their crops rice probably taken from the fields of the Caro- 

 linas and Georgia, which indicates that within six hours they had flown the 

 three or four hundred miles intervening at about the rate of a mile a minute. 



The rate of flight of a species must be sufficiently rapid to enable it to exist, 

 and so perform its part in the economy of nature. 



Birds find distant food by the senses of sight and hearing mainly. The sense 

 of smell is not highly developed, but the other perceptive powers are remarkable. 

 The perfection of sight in birds is almost incomprehensible to those who have not 

 studied the organs of vision. The keen eye of the hawk has become proverbial. 

 The perfection of sight in birds is almost incomprehensible to those who have not 

 the eyes of other vertebrates. It is provided with an organ called the pecten, by 

 which, so naturalists believe, the focus can be changed in an instant, so that the 

 bird becomes near-sighted or far-sighted at need. Such provision for changing 

 the focus of the eye is indispensable to certain birds in their quick rush upon 

 their prey. Thus the osprey, or fish-hawk, flying over an arm of the sea, marks 

 its quarry down in the dark water. As the bird plunges swiftly through the air 

 its eye is kept constantly focused on the fish, and when within striking distance 

 it can still see clearly its panic-stricken prey. Were a man to descend so suddenly 



90 



