284 



A HISTORY OF BIRDS 



pointed feathers of the breast and neck. At any rate, by this 

 tendency of the feathers and autotomy at a certain definite 

 period, revealing at the nuptial season a hitherto concealed 

 "nuptial dress," the necessity of a weakening and dangerous 

 moult is obviated. 



We may have a clue to the mystery in the abrasion pheno- 

 mena which obtains in such birds as the Curlew or the tail 

 feathers of the Duck, for example. Here, as in the long inner 

 secondaries of the Curlew, the pale-coloured areas of each feather 

 drop away just before the annual moult sets in. The darker 

 central areas are unaffected, and hence the edge of each feather 

 ultimately assumes a peculiar jagged appearance. It would 

 seem, therefore, as though the increased pigmentation was 



correlated with increased wear- 

 ing powers. Thus, if the nor- 

 mal life of slightly pigmented 

 feathers is, say, six months, by 

 an increase in the quantity of 

 colouring matter, the lasting 

 powers of the feathers are ex- 

 tended, and in some way secure 

 the bird against the necessity 

 of a double moult. The less 

 pigmented portions fall off at 

 the end of the normal life of 

 the feather, say, six months ; 

 while the more vividly coloured 

 would appear to retain vitality longer, and so delay the stimulus 

 to moulting. 



While there can be no question but that the vast majority of 

 birds which assume a nuptial dress do so through the agency of 

 moulting, it is stoutly maintained by many that a considerable 

 number of species assume the nuptial livery not by moulting but 

 by the infusion of pigment into feathers till then uncoloured. 

 Thus the brown hood of the " Black-headed" Gull is supposed 

 to be acquired. According to Gatke the dark pigment appears 

 first at the edges of the feathers and gradually extends inwards 

 until the whole feather is darkened. The black breast of the 

 Dunlin is said to be acquired after a similar fashion, but as a 

 matter of fact it is not, but is acquired by moulting. 





III. 31. — Throat OF House-sparrow 

 Showing the Difference Pro- 

 duced BY Abrasion between 

 THE "Winter" (right-hand) and 

 "Summer" (left-hand figure) 

 Plumages 



