EVOLUTION OF THE COLORS OF BIRDS. 275 



while the blues and yellows are doubtless the result of 

 sexual selection. The red appears to be generally a 

 mere intensification of the yellow, in accordance with 

 the principle of correlative colors. The adults are alike 

 and the young similar to them, but with the more special 

 color marks absent. 



ORDER COCCYGES. THE CUCKOOS, TRO- 

 GONS, KINGFISHERS, ETC. 



FAMILY CUCULID.E. THE CUCKOOS, ANTS, ETC. 



The three North American genera of this family are 

 entirely unrelated so far as their colors are concerned, 

 and accordingly must be considered singly. With re- 

 gard to protective mimicry in this group, Dr. Stejneger 

 says:* " The cuckoo (Guculus canorus), in different local 

 forms, occurring all over the Palaearctic region, and 

 wandering south in winter, is astonishingly like, in ex- 

 ternal appearance, some of the smaller hawks, not only 

 in color, but also in its manner of flight, a resemblance 

 which in Europe caused the superstition that the young 

 cuckoo in the autumn turns into a hawk. * 

 Some Oriental cuckoos belonging to the nearly allied 

 genus Hierococcyx carry the Accipitrine resemblance 

 still further, as the young birds have the dusky mark- 

 ings on the lower surface longitudinal, as in many hawks 

 and falcons, later on, like them, changing into a plum- 

 age transversely barred. This similarity is not acci- 

 dental, but evidently a case of protective mimicry, a 

 supposition greatly strengthened by the fact that we 

 know of some small Malaccan cuckoos (Penthoceryx), 

 rusty brown above, and white beneath, barred with 

 dusky, which, in size, color, and general habits most 



* Riverside Natural History, p. 374. 



