38 NATURAL SELECTION II 
snowfields and icebergs. The polar bear is the only bear 
that is white, and it lives constantly among snow and ice. 
The arctic fox, the ermine, and the alpine hare change to 
white in winter only, because in summer white would be 
more conspicuous than any other colour, and therefore a 
danger rather than a protection; but the American polar 
hare, inhabiting regions of almost perpetual snow, is white all 
the year round. Other animals inhabiting the same Northern 
regions do not, however, change colour. The sable is a good 
example, for throughout the severity of a Siberian winter it 
retains its rich brown fur. But its habits are such that it 
does not need the protection of colour, for it is said to be able 
to subsist on fruits and berries in winter, and to be so active 
upon the trees as to catch small birds among the branches. 
So also the woodchuck of Canada has a dark-brown fur; but 
then it lives in burrows and frequents river banks, catching 
fish and small animals that live in or near the water. 
Among birds, the ptarmigan is a fine example of protective 
colouring. Its summer plumage so exactly harmonises with 
the lichen-coloured stones among which it delights to sit, that 
a person may walk through a flock of them without seeing a 
single bird; while in winter its white plumage is an almost 
equal protection. The snow-bunting, the jer-falcon, and the 
snowy owl are also white-coloured birds inhabiting the arctic 
regions, and there can be little doubt but that their colouring 
is to some extent protective. 
Nocturnal animals supply us with equally good illustrations. 
Mice, rats, bats and moles possess the least conspicuous of 
hues, and must be quite invisible at times when any light 
colour would be instantly seen. Owls and goatsuckers are of 
those dark mottled tints that will assimilate with bark and 
lichen, and thus protect them during the day, and at the 
same time be inconspicuous in the dusk. 
Tt is only in the tropics, among forests which never lose 
their foliage, that we find whole groups of birds whose chief 
colour is green. The parrots are the most striking example, 
but we have also a group of green pigeons in the East; and 
the barbets, leaf-thrushes, bee-eaters, white-eyes, turacos, and 
several smaller groups, have so much green in their plumage 
as to tend greatly to conceal them among the foliage. 
