PDF - Wallace Online

38 NATURAL SELECTION insnowfields and icebergs. The polar bear is the only bearthat is white, and it lives constantly among snow and ice.The arctic fox, the ermine, and the alpine hare change towhite in winter only, because in summer white would bemore conspicuous than any other colour, and therefore adanger rather than a protection; but the American polarhare, inhabiting regions of almost perpetual snow, is white allthe year round. Other animals inhabiting the same Northernregions do not, however, change colour. The sable is a goodexample, for throughout the severity of a Siberian winter itretains its rich brown fur. But its habits are such that itdoes not need the protection of colour, for it is said to be ableto subsist on fruits and berries in winter, and to be so activeupon the trees as to catch small birds among the branches.So also the woodchuck of Canada has a dark-brown fur ;butthen it lives in burrows and frequents river banks, catchingfish and small animals that live in or near the water.Among birds, the ptarmigan is a fine example of protectivecolouring. Its summer plumage so exactly harmonises withthe lichen-coloured stones among which it delights to sit, thata person may walk through a flock ofthem without seeing asingle bird while in;winter its white plumageis an almostequal protection. The snow-bunting, the jer-falcon, and thesnowy owl are also white-coloured birds inhabiting the arcticregions, and there can be little doubt but that their colouringis to some extent protective.Nocturnal animals supply us with equally good illustrations.Mice, rats, bats and moles possess the least conspicuous ofhues, and must be quite invisible at times when any lightcolour would be instantly seen. Owls and goatsuckers are ofthose dark mottled tints that will assimilate with bark andlichen, and thus protect them during the day, and at thesame time be inconspicuous in the dusk.It is only in the tropics, among forests which never losetheir foliage, that we find whole groups of birds whose chiefcolour is green. The parrots are the most striking example,but we have also a group of green pigeons in the East ;andthe barbets, leaf-thrushes, bee-eaters, white-eyes, turacos, andseveral smaller groups, have so much green in their plumageas to tend greatly to conceal them among the foliage.