. The bird, its form and function . of change incolour, namely, the wearing off of the brittle tips of thefeather-vane. An excellent example of this is seen in theSnowflakes, which come south in the depth of severewinters, flying in small flocks about our fields, like ananimated flurry of the actual crystals. When we seethe birds at this time they are brownish and brow^nishwhite. In the spring, in their northern home, they changeto a clear-cut black and white, not by shedding the entireplumage, but merely by the breaking off of the brownfeather-tips. By a similar process the Bobolink changesfr
. The bird, its form and function . of change incolour, namely, the wearing off of the brittle tips of thefeather-vane. An excellent example of this is seen in theSnowflakes, which come south in the depth of severewinters, flying in small flocks about our fields, like ananimated flurry of the actual crystals. When we seethe birds at this time they are brownish and brow^nishwhite. In the spring, in their northern home, they changeto a clear-cut black and white, not by shedding the entireplumage, but merely by the breaking off of the brownfeather-tips. By a similar process the Bobolink changesfrom the buffy female dress to his rich black-and-whitespring suit, and, as we saw in Chapter II, Fig. 35, theEnglish Sparrow gains his cravat of jet. Another excellent example is found in the Black Larksof Siberia, the males of which, in winter, are of an almostuniform sandy colour, like a Skylark, but by the wearingoff of the buff tips of the feathers, the birds become jet-blackin the summer—a most remarkable and radical The Body of a Bird 299 The relation of a birds colours to its haunts and itshabits of life is a subject of intense interest. This is,of course, not in the same category as the subjects of theforegoing paragraphs, but indeed includes them all. Themost common class of colours is known as are such that the bird resembles its environmentor surroundings and is thus given a better chance of escap-ing the observation of its enemies. It is evident that,in a study of this nature, observation of the bird in itsnatural haunts is of far greater value than any othermethod. We find that the majority of sparrows, sandpipers,and quail are gray or brown, like the grasses, sedges, andleaves among which they live; w^hile the birds w^hichspend their lives higher up among the branches of treesare greenish, or at least more brightl} coloured. Many birds which are protectively coloured are darkabove and white or whitish beneath. The significanceof this pat
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