Protective Coloration 199 



aquatic forms have been shown to lose their color when removed from 

 light. Blind cave amphibians and fishes with little or no color have 

 been found to develop abundant pigment in the skin after exposure 

 to normal daylight (Rasquin, 1947). Intense radiation may be harm- 

 ful because of undue heating or evaporation, because of the lethal 

 action of the ultraviolet component, or in other ways. 



The excessive absorption of light by animal tissues must also be 

 avoided. Most animals simply move into the shade, burrow into 

 the ground, or descend to deeper levels in the water. The develop- 

 ment of a relatively transparent body would appear also to help deal 

 with this problem. Since only the radiation that is actually absorbed 

 can be effective, the highly transparent tissues of many types of plank- 

 ton can retain but little light energy. This fact may enable some 

 planktonic animals to endure higher light intensities in the surface 

 waters than would otherwise be possible. As we shall see, many 

 species of plankton are extremely sensitive to light. In other kinds 

 of animals evolutionary development has gone in the opposite direc- 

 tion with the production in the skin of abundant pigment which pro- 

 tects the deeper tissues. Anyone who has lain too long on the beach 

 in June has been painfully aware of the harmful effect of excessive 

 radiation on animal tissue and is familiar with the deposition of pig- 

 ment in the skin of man to produce tan. In addition, transparency or 

 pigment patterns also serve to render animals less conspicuous. 



Protective Coloration. The pigmentation of a great many animals 

 forms a coloration that appears to afford protection from enemies. 

 One very common type of protective coloration is a simple matching 

 of the background in respect to color and pattern. A quail squatting 

 in the grass or a bittern standing motionless among the swamp reeds 

 is exceedingly difficult to distinguish from its surroundings, as is a 

 moth on the bark of a tree or a katydid among green leaves. Many 

 other instances of remarkably close resemblance of birds, insects, and 

 other animals to their background will occur to the reader. A second 

 common type of protection, often combined with the first, is oblitera- 

 tive shading in which the bird, mammal, or fish displays darker pig- 

 mentation on its back and lighter color underneath. This difference 

 tends to counteract the stronger illumination received from above 

 with the result that the animal blends with its background. 



The protective aspect of other color patterns may result chiefly from 

 the confusion of the enemy by the disruption of the animal's usual 

 outline. Birds with necks or heads of contrasting colors or tropical 

 fish with strong transverse stripes are not easily recognized by man 

 under certain conditions of illumination because of the unexpected 



