BIRDS. 557 



protection. There can, however, be no doubt, as formerly 

 remarked, that both sexes of many birds have had their 

 colors modified so as to escape the notice of their enemies; 

 or in some instances, so as to approach their prey unobserved, 

 just as owls have had their plumage rendered soft, that 

 their flight may not be overheard. Mr. Wallace remarks * 

 that " it is only in the tropics, among forests which never 

 lose their foliage, that we find whole groups of birds whose 

 chief color is green." It will be admitted by every one 

 who has ever tried how difficult it is to distinguish parrots 

 in a leaf-covered tree. T^everthelesss, we must remember 

 that many parrots are ornamented with crimson, blue and 

 orange tints, which can hardly be protective. AVood peckers 

 are eminently arboreal, but besides green species there are 

 many black and black-and-white kinds all the species 

 being apparently exposed to nearly the same dangers. It 

 is therefore probable that with tree-haunting birds strongly 

 pronounced colors have been acquired through sexual selec- 

 tion, but that a green tint has been acquired oftener than 

 any other from the additional advantage of protection. 



In regard to birds which live on the ground, every one 

 admits that they are colored so as to imitate the surround- 

 ing surface. 3ow difficult it is to see a partridge, snipe, 

 woodcock, certain plovers, larks and night- jars when 

 crouched on ground. Animals inhabiting deserts offer the 

 most striking cases, for the bare surface affords no conceal- 

 ment, and nearly all the smaller quadrupeds, reptiles and 

 birds depend for safety on their colors. Mr. Tristram has 

 remarked in regard to the inhabitants of the Sahara, that 

 all are protected by their " isabelline or sand color, "f 

 Calling to my recollection the desert-birds of South 

 America, as well as most of the ground-birds of Great 

 Britain, it appeared to me that both sexes in such cases 

 are generally colored nearly alike. Accordingly, I applied 

 to Mr. Tristram with respect to the birds of the Sahara, 

 and he has kindly given me the following information: 

 There are twenty-six species belonging to fifteen genera, 

 which manifestly have their plumage colored in a protect- 



" Westminster Review," July, 1867, p. 5. 



f " Ibis," 1859, vol. i, p. 429, et seq. Dr. Rohlfs, however, re- 

 marks to me in a letter that, according to his experience of the 

 Sahara, this statement is too strong. 



