304 THE STRUCTURE AND LIFE OF BIRDS chap. 



Protective Coloration. 



On one point every one is in agreement — viz., that 

 many birds are protectively coloured. They escape 

 the hungry eyes of birds of prey, reptiles, and other 

 enemies, from the fact that they are of the same colour 

 as their surroundings. The birds of the Sahara are 

 most of them sandy-coloured. Pallas's Sand-grouse, 

 a native of desert tracts north of the Himalayas, must 

 be familiar to most people. The sober browns and 

 grays of our common birds are well suited to their 

 life in woods which half the year are leafless, whereas 

 the evergreen tropical forests afford concealment for 

 more conspicuous plumage. The Ptarmigan drops 

 his dark summer dress for one of a pure white that 

 may make him almost invisible on the winter snows. 

 The Canary Islands have two very remarkable 

 instances of this adaptation to surroundings. There 

 is a Chaffinch (Fringilla teydea) that lives among 

 the pine trees on the high slopes beneath the peak of 

 TenerifTe, and to harmonise with the glaucous hue of 

 the pine trees, he has become a beautiful blue-gray. 

 There is no doubt that this bird is a descendant of 

 European Chaffinches. Teneriffe is a volcanic island, 

 thrown up from the bottom of the ocean, and it has 

 only upon it such animals as have found their way 

 over sea, though these have often been curiously 

 modified. The Trumpeter Bullfinch is of a uniform 

 bright salmon colour, but on the ochre-coloured 

 rocks of the nearly desert island of Hiero he is ex- 

 tremely difficult to see. In the Natural History 



