473 
and Colour-change in Birds. 
IV. That there is considerable evidence to show that pigment 
may, by a purely physical process, find its way into a 
fully-formed feather. 
It may, perhaps, not be out of place here to recapitulate 
briefly the various methods by which birds effect 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 all 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, secondaries, and tail-quills, 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 primaries at once, e. g. Creoc , 
Anas , Gallinula , Colymbus , 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 then 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 colour 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 schceniclus), in the head 
and back of the Brambling ( FringiUa montifringilla) , in the 
throat of the Redstart ( Ruticilla phoenicurus) , 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 a much brighter appearance. 
