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 
Teneriffe, 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 sce. In the Natural History 
