THE THREE GREAT PROBLEMS OF BIRD LIFE. 137 



up bis little ones will have a large effect upon his shape, his 

 color, and his habits. If you knew nothing of a bird but 

 what he fed on, how he got it, and how he nested, you could 

 tell a great deal about his appearance. It was that you might 

 better understand what is to follow concerning the changes 

 of a bird's structure, color, and habits that are brought about 

 by the way he solves these problems of bird life, that I asked 

 you to suppose that you were plain birds. 



