28o A HISTORY OF BIRDS 



noted, by moulting, but by shedding the tips to the feathers, 

 and also the outer surface of the barbs and barbules, as in the 

 Linnet, Chaffinch, Brambling, House-sparrow and Snow Bunt- 

 ing, for instance (p. 284). 



In these birds the feathers assumed at the autumn moult 

 have long brown or grey tips, as the case may be, which impart 

 to the bird the sober colours of winter. If the plumage be care- 

 fully examined, however, the greater part of the feather will be 

 found to present the colours characteristic of spring, but dulled. 

 As the breeding season approaches these dull-coloured tips 

 are shed, thereby exposing the surface previously overlapped. 

 These tips, in short, have served the purpose of a "dust-cloak," 

 keeping the spring dress clean during the winter months, and 

 so saving a new dress ! 



So far, it would appear, a double moult is mainly — and 

 perhaps we shall find always, when we arrive at a correct inter- 

 pretation of the facts — confined to those species which assume 

 alternately a dull and a brightly coloured livery. Further, as 

 we have already hinted, the facts seem to show that there is a 

 tendency to eliminate the dull-coloured phase of plumage, as 

 may be seen in the Ducks, which put on what answers to the 

 "nuptial" dress of the Plovers in the autumn, wearing the dull 

 plumage for a few weeks only. 



On the assumption that the double moult is a primitive 

 character — and this seems tolerably certain — it is curious that, 

 in species where the males develop alternately a dull with a 

 multi-coloured plumage, the males alone seem to go through 

 this double moult. 



A very definite order in the succession of the new feathers 

 is met with, an order which will probably be found to differ 

 with different species. As to the variations thereof we know 

 little enough. Whether this order corresponds with the original 

 appearance of the feathers in the assumption of the first plumage 

 remains to be seen ; but, as a general rule, it would appear to 

 do so, except, at any rate^ in so far as the quills are concerned. 

 Even here, however, this rule is followed by the Ducks, Rails 

 and Grebes where the quills are shed all at once, leaving 

 the birds for a time helpless as to flight. Selection, how- 

 ever, has in the majority of birds brought about an arrange- 

 ment whereby the power of flight is retained throughout the 



