and Colour -chuntic in Birds. 473 



IV. That there is considerable evidence to show that pigment 

 may, by a purely physical process, find its way into a 

 fully-formed feather. 



Tt may, perhaps, not be out of place liere to recapitulate 

 briefly the various metliods by which birds cfJ'ect a change of 

 colour in their plumage. 



Firstly, there is the ordinary moult, or actual replacing of 

 old feathers by new ones. This may be complete, involving 

 a change of a// the feathers, or partial, in which only certain 

 tracts are concerned. A partial moult may affect only 

 certain parts, and be undergone for the purpose of assuming 

 a distinct breeding-dress, e.g. head and neck of the Red- 

 throated Diver in spring; or it may apply to all feathers 

 except the primaries, sccondai-ies, and tail-(iuills, e.g. most 

 young birds of the Passeres in their first autumn, and many 

 species of Passeres in spring ; or, again, only to certain tracts, 

 the moult being replaced by change of colour in other tracts, 

 e.g. the Golden Plover (see above), or not at all, as the case 

 may be. For simplicity's sake, it is best to consider the 

 moult of the quills quite apart from that of the small 

 feathers, although it takes place only where a moult of the 

 small feathers is going on. Many species of birds in widely 

 different groups moult all their [)rimaries at once, e. g. Crex, 

 Anas, GaUinula, Cohjmbus, Alca, Uria ; but as a rule these 

 feathers are moulted regularly in pairs, beginning at the 

 innermost primary and secondary. In some species all the 

 primaries are moulted first, in pairs, and tlien the second- 

 aries, for instance in Machetes. 



Secondly, there is abrasion, which consists in the wearing 

 off of the edges of the small feathers, revealing the colour 

 at the base, and so producing a change of eolonr in the 

 plumage. This is the commonest form of abrasion, and may 

 be well seen in many Passerine birds, e. g. in the head of 

 the male Reed-Bunting (Emberiza sc/i(eniclus), in the head 

 and back of the Brambling {Fringilla montifringilla) , in the 

 tliroat of the Redstart (Ruticilla phcenicurus), and in many 

 others. In some species it goes a stage further, and the 

 radii of the feathers are cast, leaving the colour in the rami 

 exposed, and giving the bird u much brighter appearance. 



