vi FORM AND FUNCTION 155 



Moulting. 



Moulting, as I have already said, is a reptilian 

 characteristic, and corresponds to the shedding of 

 the horny covering of the scales. It is due to the 

 papilla which once more extends into the quill 

 and causes the feather to fall off. In the Cassowary 

 and Emeu the tip of the new feather extends into 

 the base of the old one, which it carries for a time, 

 but the two are only connected mechanically. 

 They do not, like the nestling down and the feather 

 that follows it, make up one organ. Most birds 

 moult completely in the summer or autumn. 

 Many have a partial moult, at which only small 

 feathers are shed, in spring. It is sometimes stated 

 that migratory birds have two complete moults, 'one 

 before each migration, but it is probable that none of 

 them shed their great quill feathers more than once. 

 The Cuckoo's main moult is believed to be in spring : 

 sometimes he has arrived in England before its comple- 

 tion. In autumn, after he has left us, the smaller feathers 

 are once more changed. Swifts also, it is supposed, 

 moult in early spring long before they come to us, 

 a slighter moult taking place after their departure. 

 Swallows and Martins moult only once — in very 

 early spring or even in winter — being distinguished 

 by this from the Swifts, which moult twice. With 

 most migrants, as with other birds, autumn is the 

 great season for donning new feathers. Spring is the 

 time when the wedding plumage is put on, and the 

 Ruffs, the Golden Hovers, the Dunlins, the Linnets, 



