PRINCIPLES OF PROTECTIVE COLOURATION 217 



The true explanation flashed into my mind to-day as 1 was 

 watching a bittern standing at a distance of about ten feet. The 

 light stripes on the bill were repeated and continued by the light 

 stripes on the side of the head and neck and together they 

 imitated very closely the look of the separate bright reed-stems 

 while the dark stripes pictured reeds in shadow or the shadowed 

 interstices between the stems. The truth of this explanation 

 must be apparent to any one with an eye for these things who 

 watches a bittern standing motionless among reeds." The 

 deduction is of course that those who were clever enough to 

 detect the bittern in the forlorn attempt to look like a stick 

 really only did so because, owing to defects in the background 

 or to the unusual standpoint of his observer, his attempt to 

 disappear into reeds had broken down and his colour scheme 

 was for the moment a failure. When it was succeeding he was 

 practically never seen. But if the bittern and the tiger and the 

 coral snake use stripes as a concealment, why not the zebra ; 

 and if the zebra cannot be accused of trying to look like 

 anything, why should it not, in common with many another 

 owner of "conspicuous markings," be really succeeding in 

 disappearing ? 



This is an implication which Thayer at any rate is pre- 

 pared to welcome — even to the extent of applying it to 

 humming-birds ! Of these Thayer writes that thanks to irides- 

 cence " their changeableness of colour often ranges from dull 

 velvety soot-colour to the intensest gleaming of pure red, 

 blue, green, orange or purple, as the case may be, and. some- 

 times several of these bright colours co-exist in the same 

 feathers, showing either separately in different lights or 

 intermixed in one light. But the change from one bright 

 colour to another is less characteristic of humming-birds' 

 iridescence than the change from dull black to keenest bright- 

 ness. It is in the fullness of this change and the extreme 

 brilliancy of the high-light tints that the supremacy of their 

 coloration lies. Behind the dazzling scintillating blaze of its 

 jewelled head, how can the little round body of a humming- 

 bird be seen ? " 



"That shifting blaze of red or green or purple light, one 

 instant partly clouded over and in the next flashing out into 

 the sharpest sunlike sparkles, completely eclipses and masks 

 the form and solidity of the body, now veiling it and now 



