EVOLUTION OF THE COLORS OF BIRDS. 265 



FAMILY CRACID.^. The Curassows and Guans. 



Genus Ortalis. The Chachalacas. 



Only one species of this genus comes within our limits, 

 and it has the appearance of being a form which has 

 deteriorated from some more brilliant phase of plumage. 



ORDEK COLUMB^. THE PIGEONS. 



FAMILY COLUMBID^. The Pigeons or Doves. 



The North American representatives of this family- 

 are not so remarkable for the brilliancy of the plumage 

 as is the case with many extralimital species, but the 

 tints are beautifully soft and pleasing, with metallic 

 tints of the less pronounced sort. All the genera, and 

 frequently different species of the same genus, are dis- 

 tinguished by characteristic white and black recognition 

 marks, principally on the wings or tail (see ante p. 205), 

 or frequently on both — these being especially important 

 in this family from the fact that the birds generally as- 

 sociate in flocks, often of immense size. I do not think 

 it can be held that the other colors of the family are of 

 any utility whatever. In an old cosmopolitan group of 

 birds like this hereditary tendencies have been fixed for 

 indefinitely long periods, and it may well be that all the 

 North American genera are mere side shoots from the 

 main stem, colored in the prevailing hues of the type — 

 plumbeous, bluish gray, reddish or chestnut, with black 

 and white, and varied with some mild iridescent tints. 

 These colors may doubtless have first been acquired by 

 sexual selection, Ijut what factors may have come into 

 play in the establishment of the colors of the genera 

 found within our limits is far too complex a question to 

 discuss without a knowledge of the entire order. It 

 need only be remarked here that sexual selection in 

 conjunction with isolation, has undoubtedly had a more 



