EVOLUTION OF THE COLORS OF BIRDS. 207 



we suppose the various species of this genus to be the 

 descendants of a common ancestor, we can hardly in- 

 terpret this great diversity in the distribution of the 

 bars on the tail to any principle but natural selection 

 producing discriminative recognition marks. 



The tail-markings among' the Caprimulgidae are pe- 

 culiarly characteristic. They are interesting because, 

 instead of affording merely specific distinctions, they 

 form generic characters also. In the whip-poor-wills 

 (Antrostomus) the three outer tail feathers are tipped 

 with white on the inner web in the male. In. the poor- 

 will (Phalcenoptilus) all but the inner pair are broadly 

 tipped with white in the male, and less broadly in the 

 female. The tail markings in the parauque (Nyctidro- 

 mus) are very peculiar. They are thus- described in 

 Ridgway's Manual: " Outer tail-feathers nearly uniform 

 blackish; next mostly white, the outer web edged with 

 dusky; four middle tail-feathers without any white, 

 their ground-color mottled brownish-gray, relieved by 

 irregular ' herring-bone ' blotches of dusky along the 

 shaft." In the night-hawks (Chordeiles) the males have 

 a broad bar of white on all but middle feathers near the 

 tip of the tail. The variations in the tail patch of the 

 different forms of the genus Antrostomus presents so 

 many interesting features that a tabular view of them 

 may serve to bring the points before the mind: 



