THE 



AMERICAN NATURALIST 



Vol. XLVIII July, 19U No. 571 



PATTERN DEVELOPMENT IN MAMMALS 

 AND BIRDS 



GLOVER M. ALLEN, 



Boston Society of Natural History 



The particular coloring of mammals and birds is pro- 

 duced by two factors — pig-mentation and the physical 

 structure of the hair or feathers. Both are often present 

 together. In certain mammals, for example the golden 

 mole (Chrysochloris) and the European Galemys, a 

 beautifully iridescent sheen is produced by the reflection 

 of light rays having a certain angle of incidence upon the 

 hair- which themselves contain pigment of a character- 

 istic color. In the duckbill (Ornithorhynchus) the same 

 thing is found. The peculiarity of feather structure that 

 causes iridescence is largely developed in certain families 

 of birds, as the hummingbirds and the pigeons (see 

 Strong, 1904, for an account of the feather structure). 



It is not my purpose to discuss the use of this irides- 

 cence to the bird, beyond stating my belief that it is in 

 part at least for sexual display, as no one can doubt who 

 watches the male street pigeon strutting before his mate. 

 With amorous coos and lowered head, he confronts her 

 and, swelling out his throat feathers, turns about and 

 about, so that the light is reflected from his neck and 

 throat in a sparkle of rainbow hues. It has also been 

 suggested (Thayer, 1909) that iridescence may be a 

 strong factor in concealment, since from the variety of 

 the colors produced the bird is more difficult to resolve 

 from its many tinted environment amid foliage and 

 flowers. 



