Protective Coloration 201 



attempting to explain the evolutionary origin of this sex difference, 

 Darwin drew attention to the courtship antics of peacocks, pheasants, 

 and other birds, in which the males appear to vie with one another 

 in showing off their plumage. Darwin proposed that the special 

 plumage of the male evolved after many generations in which the 

 females selected and mated with the "most beautiful" birds. Since 

 we have no reason to suppose that birds judge the attractiveness of 

 male suitors on the same basis as we would, this explanation seems 

 unsatisfactory. As yet no convincing demonstration has been made 

 of any basis for selection or of any other method by which the elab- 

 orate decoration of the male may have arisen. 



The duller coloration characteristic of the female is undoubtedly 

 related to her greater need for concealment while brooding the eggs. 

 The striking coloration of the males of many species can rarely have 

 any protective value for the male himself, although his conspicuous- 

 ness might draw attention away from the female on the nest. In some 

 birds, such as Wilson's phalarope, the tables are turned, for the fe- 

 males are brightly colored and the drab males do the housework of 

 incubating the eggs. Difference in appearance may play a useful 

 part in aiding sex recognition. The brilliant breeding plumage of 

 the male is often replaced by a duller garb during the winter season. 

 The length of day has been shown to influence breeding, migration, 

 and color change in many birds and mammals. The light factor may 

 thus be involved in coloration through its effect on reproductive ac- 

 tivities as well as through its role in protective resemblance, and the 

 two may be interrelated. 



Mention was made in earlier chapters that desert animals charac- 

 teristically display a pale coloration in contrast to the darker hue of 

 the inhabitants of humid regions. Although temperature, moisture, 

 and light may directly affect the general color of terrestrial animals 

 under some circumstances, these factors often act indirectly through 

 their influence on the color of the ground in relation to the conceal- 

 ment of the animals. Evidence indicates that pale or dark coloration 

 has evolved in many species and races as a result of selective survival 

 as influenced by their conspicuousness against the background. Se- 

 lection would thus account for the occurrence of a white mouse 

 {Perognathus apache) inhabiting an area of white gypsum sands in 

 New Mexico and of a black mouse (P. intermedins) living on an ad- 

 joining area of black lava (Benson, 1933). The possibiHty that cli- 

 mate sometimes exerts a direct effect, however, is suggested by the 

 fact that nocturnal animals in the desert have the same pale coloration 



