[4] BIRDS OF OREGON 



terest, but few notice the intricate patterns in soft grays and whites that 

 decorate a male Gadwall's breast. 



Since Darwin propounded his theories of protective coloration and 

 sexual selection many other theories have been advanced to account for 

 the remarkable color patterns and plumage variations to be found in 

 birds. In a book of this kind there can be little more than mention of 

 those theories more commonly considered as accounting for these color 

 patterns. They are all interesting, but no one theory has been accepted 

 in its entirety by all biologists. 



The theory of protective coloration assumes that a bird or other animal 

 may be colored so like the background against which it habitually lives 

 that it escapes detection as long as it remains motionless. Striking ex- 

 amples are seen in grouse and prairie chickens, which flatten themselves 

 into invisibility against the ground as long as they do not move. The 

 longitudinal brown and yellow stripes of bitterns strikingly simulate the 

 light and shadows of the reed patches in which they habitually live. 

 Even brilliantly colored birds may be protected by the breaking-up of the 

 pattern. For example, a White-headed Woodpecker might be a con- 

 spicuous bird, but in many situations the striking contrast between the 

 black body and white head actually seems to behead the bird and make 

 it appear a black or white spot against the background. Even such bril- 

 liantly colored birds as the tanagers and the warblers may be concealed 

 by their pattern as long as they remain motionless in the treetops, the 

 contrasting colors having the effect of breaking up the outline and render- 

 ing the bird more difficult to see. The art of camouflage, developed to a 

 considerable degree in military and naval operations in the Great War, is 

 recognition of this fact. 



The theory of sexual selection was advanced to account for the brilliant 

 colors of the male birds. The theory presupposes that by conscious or 

 unconscious selection of the more strikingly marked males, special char- 

 acters or brilliant colors have been gradually developed over a long time. 

 This might account for the crests of some species of birds, the aigrettes 

 and plumes of some of the herons, the wattles and combs of the turkeys, 

 and the brilliantly colored air sacs of the grouse. The same theory also 

 has been used to account for the development of highly colored beaks and 

 varied feathers in many species. 



The latest theory, advanced by Abbott H. Thayer, is that of counter 

 shading. Thayer, artist and demonstrator, pointed out the prevalence of 

 dark backs and light under parts in the animal world and demonstrated 

 that such a pattern had some concealing value against almost any back- 

 ground in comparison with a solid-colored body of the same size and 

 shape. 



Many marks in birds may not be accounted for by any of the above 

 theories, and for these, the theory of recognition marks or revealing 



