4 USEFUL BIRDS. 
hood of New York have had in their crops 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 proportion to the size of its owner than are 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 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 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 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 eye, 
in like manner utilizes the pecten in the pereeption, pursuit, 
and capture of its prey. Most 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- 
1 American Ornithology, Wilson and Bonaparte, Vol. IV, pp. 319, 320. Evi- 
dently a quotation from Audubon’s Ornithological Biography. 
