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 fra3'ing 



Fig. 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 verv 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 



