WHAT IS A BIRD 1 23 



Once a year at least every bird dons a new- 

 suit. This is done by a process known as moult- 

 ing, during which the old feathers are cast off 

 and replaced by new ones. In the lizards and 

 snakes the external layer of the skin is thrown 

 off more or less whole, much as is the shell 

 of the lobster or crab, but in the bird it is 

 done much more gradually. The feathers are 

 cast separately, their places being immediately 

 filled by new ones. These are at first en- 

 closed in a thin blue sheath which breaks 

 away in flakes near the tip, and slowly exposes 

 the gradually unfolding feather within. Some- 

 times this sheath remains whole for a very 

 considerable time, and thus gives the bird the 

 appearance of having spines mixed up with its 

 plumage. 



As a rule the moult begins at the end of the 

 breeding season so that the old dress, worn with 

 the work entailed in rearing a family, may be 

 discarded and gradually replaced. Some moult- 

 ing however takes place, in the case of certain 

 male birds, before the period of courtship begins. 

 At this time they assume the purely decorative 

 part of their plumage, and throw it off again 

 after the serious business of life is over. 



Swans, geese and ducks, moult all the quills 

 at once, so that for a time they are flightless. 

 During this time they remain in the strictest 

 seclusion, sometimes even throwing off their 

 characteristic male attire to don the more 

 sombre garb of the female, and thus to render 

 themselves less conspicuous. In the case of certain 

 ducks, when both male and female, and young, 



