BIRDS, THEIR STRUCTURE AND ADAPTATIONS 291 



The bird's eye is a very wonderful instrument, the sight being 

 keen both at a distance and for close vision, and the change of 

 focus is very quickly made. This is necessary in birds, because 

 they must see clearly to pick up food at their feet, or detect an 

 enemy at a distance, observe their prey far off, or weave a nest 

 close at hand, and their ability along this line is unequaled by any 

 other animal. 



Their hearing is usually acute though there are no external ears, 

 the openings being protected by a ring of feathers. Keenness of 

 this sense is useful to escape danger and to recognize the songs 

 and calls of their mates. 



COLLATERAL READING 



General Structure: Textbook of Zoology, Parker and Haswell, pp. 357- 

 366; Textbook of Zoology, Shipley and McBride, pp. 495-506; Winners 

 in Life's Race, Buckley, pp. 123-130; Forms of Animal Life, Rolleston, 

 pp. 46-66; Textbook of Zoology, Claus and Sedgwick, pp. 232-238; First 

 Book of Zoology, Morse, pp. 174-180; General Zoology, Colton, pp. 208-221; 

 General Zoology, Linville and Kelley, pp. 364-373; Elementary Zoology, 

 Davenport, pp. 370-419; Elementary Zoology, Needham, pp. 211-237; 

 Practical Zoology, Davison, pp. 226-261; Elementary Zoology, Kellogg, 

 pp. 327-372; Biology Text, Peabody and Hunt, pp. 62-100. 



Flight of Birds: Animal Mechanism, Pettigrew, pp. 209-278; Animal 

 Locomotion, Marey, pp. 103-206; Winners in Life's Race, Buckley, pp. 

 130-135; Animal Life, Thompson, pp. 123-124; Textbook, Shipley and 

 McBride, pp. 501-502; Introduction to Zoology, Davenport, pp. 310-311. 



Classification and Types: Economic Zoology, Kellogg and Doane, pp. 

 273-294; Birds of Eastern North America, Chapman, entire; Bird Life, 

 Chapman, entire; Citizen Bird, Wright, entire; Textbook of Zoology, 

 Linville and Kelley, pp. 374-397; General Zoology, Colton, pp. 222-245; 

 Types of Animal Life, Mivart, pp. 66-95; Little Brothers of the Air, Miller, 

 entire; American Natural History, Hornaday, pp. 171-309; N. Y. State 

 Museum Memoir, Vols. I and II, entire; American Geographic Magazine, 

 bird numbers, entire; Bulletins of U. S. Department of Agriculture; Bulle- 

 tins of Audubon Society; Bird Guides (Land Birds, Water Birds), Reed, 

 entire. 



SUMMARY 

 Characteristics. 



Feathers, wings, beak, two feet, shelled egg. 

 1. Adaptations for flight. 



Shape, feathers to smooth outline. 

 Balance, neck, legs, attachment of wings, 



