52 The Bird 
We have seen how birds, by moulting their feathers, 
change the colour of their plumage; in some cases several 
times each year. There is, however, still another way in 
which the appearance of new colour is brought about. 
Not by increase of pigment, for the feather when once 
full grown is dead; but by the mere breaking or fraying 
Fic. 34.—The three moults of the Ptarmigan, shown in three individuals. 
(Courtesy of American Museum.) 
of the edges of each feather. It is thus that the Snow- 
flake brushes off the rusty trimmings of his winter’s suit 
and returns to his home in the far North, dressed in spick- 
and-span black and white. A much more familiar exam- 
ple is to be seen at our very doorstep. The cock English 
Sparrow in midwinter is even more sombrely clad than 
usual; but as spring approaches, although he can attain 
to no elaborate song or flowing plume, yet even this 
