INTRODUCTION 



brought their bills to the form in which we see them to- 

 day. 



Because a bird is flightless, like the Antarctic Penguins or 

 the Great Auk that formerly lived off our coast, it must not 

 be supposed that their ancestors could not fly. Probably 

 they could, and it is only the long-continued disuse that has 

 rendered them the flightless creatures they are in our day. 

 We may even imagine the prehistoric Ostrich as a bird cap- 

 able of flight. Few enemies and a life of ease on the ground 

 would gradually decrease the size and power of the wings 

 until flight was impossible. At this stage the appearance of 

 an enemy in the shape of some predatory mammal would 

 have caused the creature to take refuge by running, and after 

 a great lapse of time produce the strong-legged, swift bird 

 that we now know as the Ostrich. I mention these things 

 just to bring to attention the fact that we must not suppose 

 that birds do certain things because of unusual construction 

 adapted to that purpose, for the unusual construction follows 

 and is caused by the fact that the bird lives the hfe it does. 



Coloration. — Every bird has enemies, to escape which 

 they have to be continually on guard. Very few of them 

 live their full lives and die a natural death. Sick or crippled 

 ones fall early victims to predatory birds and animals. Col- 

 oration plays quite an important part in the protection 

 and perpetuation of each species. As a rule, female birds 

 are less conspicuously marked than their mates, a wise 

 provision, since they attract less attention at that important 

 period during which they are sitting upon their nests. 



With few exceptions, a notable one of which is the Bobo- 

 link, birds are darker on their backs than on the under parts, 

 for the reason that such gradation of tone about balances 

 the shadows caused by the overhead light and renders most 

 of them quite invisible when against the proper background, 

 whereas if they were uniformly colored they would stand out 

 very distinctly. 



Usually birds that spend the greater part of the time on the 

 ground are dull-colored and streaked with brown and gray, 

 as shown by the sparrows while those whose lives are mostly 



