BIRDS-COLOR AND PROTECTION. 485 



of many birds have had their colors modified, so as to escape 

 the notice of their enemies; or in some instances, so as to ap- 

 proach their prey unobserved, just as owls have had their plum- 

 age 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. Nevertheless, we must remember that many 

 parrots are ornamented with crimson, blue, and orange tints 

 which can hardly he protective. Woodpeckers are eminently ar- 

 boreal, 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 ac- 

 quired through sexual selection, 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 surrounding surface. 

 How 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 concealment, and nearly all the smaller quad- 

 rupeds, 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.""" Call- 

 ing 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 informa- 

 tion. There are twenty-six species belonging to fifteen genera, 

 which manifestly have their plumage colored in a protective man- 

 ner; and this coloring is all the more striking, as with most of 

 these birds it differs from that of their congeners. Both sexes 

 of thirteen out of the twenty-six species are colored in the same 

 manner; but these belong to genera in which this rule commonly 

 prevails, so that they tell us nothing about the protective colors 

 being the same in both sexes of desert-birds. Of the other thir- 

 teen species, three belong to genera in which the sexes usually 

 differ from each other, yet here they have the sexes alike. In the 



•» '"Westminster Review,' July, 1867, p. 5. 



K> 'Ibis,' 1S59, vol. 1. p. 429, et seq. Dr. Rohlfs, however, remarks to 

 me in a. letter that, according to his experience of the Sahara, this 

 statement is too strong. 

 S2 



