268 
COLOUR IN NATURE 
CHAP. 
this condition are peculiarly ugly, as the bright 
metallic feathers occur scattered among the dull 
youthful plumage. If the colours of the male 
exercise as important an influence on the choice of 
the female as is commonly asserted for birds, the 
female sun-bird must also be assumed to be possessed 
of much faith and foresight. Some at least of the 
ornamental feathers of the male are cast almost as 
soon as the breeding season is over. 
Nature of Bright Colours 
The bright colours of the sun-birds are due either 
to lipochrome pigments or to metallic structural 
colours, belonging to Gadow’s group of subjective 
structural colours. 
1. Pigmental Colours .—The colours due to lipo¬ 
chrome pigments are either yellow or bright scarlet- 
red. Brilliant patches of red or yellow feathers 
frequently occur on the throat or on the ventral 
surface, or dorsally at the root of the tail. The 
feathers so coloured are always short contour-feathers 
and not quills. The bright colour is confined 
to the apical part of the feather, the base being 
grayish or white, and the pigment occurs as usual only 
in the barbs. The barbules, if present, are grayish, 
but most frequently they are rudimentary or absent, 
so that the visible part of the feather consists of the 
diverging naked barbs, containing a considerable 
amount of bright pigment. 
2. Structural Colours .—The metallic colours of 
the sun-birds occur on feathers arranged in special 
patches on the head and throat, or as transverse 
