42 



The Bird 



37). This is also the winter phimage of the adult birds, 

 both sexes moulting alike into the rich-hued breeding 

 plumage (Fig. 38) of yellow, chocolate, and silver-gray. 



The feathers of the entire bird are moulted or fall out 

 naturally at least once a year, and in some cases twice 

 or even three times. If we were asked at what season the 



Fig. 26. — Flight-foathers of Chiiniiej- Swift clogged with .soot, showing necessity 



for moulting. 



j:)rin('ipal annual moult would be most likely to occur, 

 the fall of the year would suggest itself, and such is the 

 case, for a number of good reasons. 



T'ii-st, the hardest work which birds have to do, hatch- 

 ing and caring for their young, has, at this season of the 

 year, just been accom])lished, and has doubtless told 

 heavily on their })lumage. Breast-feathers are worn thin, 

 tails are badly frayed, and wing-pinions are broken and 

 ragged. Two alternatives confront birds at this period. 

 Those species which are to take their migratory flight 



