BIRDS 



CHAPTER 14 



Birds, because of their esthetic appeal and the mastery of flight which 

 enables them to ignore boundaries and to appear at intervals even in the 

 hearts of cities, have received a great deal, possibly more than their due share, 

 of attention. Ornithology or bird study has become almost a science in itself. 

 Since so many excellent books on birds are available, a complete discussion 

 or identification guide to them is not given here. 



A study of the anatomy of the bird will soon demonstrate adaptations 

 for flight that constitute one of the most remarkable chapters in the story of 

 evolution. A few fairly complete fossil skeletons connect the modern birds 

 with their reptilian ancestors. Two fairly complete skeletons and several 

 fragments from the Jurassic Period might well be taken for remains of some 

 of the sm.all, bipedal dinosaurs, but for the imprints of feathers. These early 

 birds, Archaeopteryx and Archaeornis, lacked the modifications of skeleton 

 necessar^?^ for flight, but probably used their well developed fingers and toes 

 for climbing, and then glided down like modern flying squirrels. A South 

 American bird, the Hoatzin, does almost the same thing today. Fossil skelc' 

 tons of two kinds of sea birds, several million years younger than the others, 

 are known as Hesperorms and Ichthyornts, and show an almost modern type 

 of bird skeleton, but possess teeth and some other reptilian skull characters. 

 The modern bird has reduced its hand to traces of three fingers and lost at 

 least one toe from each foot. Its arm and leg bones are hollow; its tail 

 shortened to a few vertebrae and a bony end-piece representing the rest; its 

 neck is long and extremely flexible, compensating for its almost rigid trunk; 

 its lungs are supplemented by air sacs, which extend from the lungs between 

 the viscera, the muscles, and even into the cavities of the hollow bones. Even 

 the outer covering of feathers is peculiarly adapted to aid flight, by re- 

 ducing air resistance. In the odd groups of birds which have lost the power 

 of flight, the feathers no longer form this smooth coat, but are downy or even 

 hair-like. 



The power of flight has permitted a remarkable development of migra- 

 tory habits. The interested student should study the main "flyways" of North 

 America, and the order and dates of movements in his locality. Now that 

 bird -banding, started about 1710 and carried on under the direction of the 

 United States Biological Survey since 1920, has given us a fairly clear picture 

 of the paths, rate of movement and destinations of birds, some of the mystery 

 has been dispelled, but by no means all. We no longer speculate, as did even 



441 



