CHAPTER XVI 



BIRDS, CONTINUED. 'OBLITERATION' BY IRIDESCENCE. CHANGEABLE COL- 

 ORS IN GENERAL; THEIR PART IN WATER-PICTURING COSTUMES, ETC. 



BRILLIANTLY changeable or metallic colors are among the strongest 

 factors in animals' concealment, and go far toward achieving 'oblit- 

 eration' without counter shading. The quicksilvejr-like intershifting of many 

 lights and colors, which the slightest motion generates on an iridescent sur- 

 face, like the back of a bird or the wing of a butterfly, greatly obscures the 

 visability of that wing or back, as such, tending to make it 'blend' inextri- 

 cably with the gleaming and scintillating, labyrinthine-shadowed world of 

 wind-swayed leaves and flowers. Even without motion, the animal's sur- 

 face, which would show all in its true place and plane if it were plainly col- 

 ored, is by its iridescence made to appear 'dissolved' into many depths and 

 distances. Here is a bright place that stands out near and clear, there a 

 dark area that melts away into'indefinite remoteness, and so on. Rarely does 

 such a 'changeable' surface, out of doors, reveal itself fully and truly to the 

 eye. Hence, iridescence is, as I have said, one of the prime factors of dis- 

 guise, and quantities of creatures profit by it. As a general rule, it is found 

 on animals that spend much of their time in lively motion. As we have seen 

 in Chapter XIII, the more minutely detailed forms of obliterative coloration 

 are not adapted to animals of this t5^e. Seldom "lying close," they need a 

 bold and simple disguise to lessen the conspicuousness of their movements. 

 This is found, as we have seen, in 'ruptive' pattern; and iridescence is equiv- 

 alent to ruptive pattern with an added gift — the power of motion. Ruptive 

 pattern, that is, with no fixed form, but mutable like the landscape itself. 



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