USEFUL BIRDS. 



hood of New York have had in their croi)s rice probably 

 taken from the fields of the Carolinas or 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 bird's eye is much larger 

 in pro})ortion to the size of its owner than are the L^yQ^^ 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 l)ird becomes nearsighted 

 or farsighted at need. Such provision for changing the focus 

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

 upon their prej'. Thus the Osprey or Fish Hawk, flying 

 oN'cr an arm of the sea, luarks its quarry down in the dark 

 water. As the bird plunges swifth^ through the air its eye 

 is kept constantly focussed upon the fish, and when within 

 striking distance it can still see clearly its panic-stricken 

 prey. Were a man to descend so suddenly from such a 

 height he would lose sight of the fish before he reached the 

 water. The Flycatcher, sitting erect upon its perch, watch- 

 ing passing insects that are often invisible to the human e^-e, 

 in like manner utilizes the pecten in the perception, i)ursuit, 

 and capture of its ^vcy. ^lost of the smaller birds will see 

 a Hawk in the sky before it becomes visible to the human 

 eye. The Vulture, floating on wide wings in upper air, 

 discerns his chosen food in the valley far below, and as he 

 descends toward it he is seen by others wheeling in the dis- 

 tant sky. As they turn to follow him they also are seen by 

 others soaring at greater distances, who, following, are pur- 



' American Ornithology, "Wilson and Bonaparte, Vol. IV, pp. 319, 320. Evi- 

 dently a quotation from Audubon's Ornithological Biography. 



