274 COLOUR IN NATURE 



Colours of Humming-birds 



Turning now to humming-birds, we find that 

 here pigmental colours are of relatively little im- 

 portance, while structural colours attain an extra- 

 ordinary beauty and brilliancy. Further, we find 

 that the place of the pigmental colours of sun-birds 

 in contrasting with and showing up the metallic 

 colours is taken in humming-birds by black and 

 white. White especially is often of great import- 

 ance in producing the general effect of beauty. 



Fig. 3. — Metallic feather from the throat of a humming- 

 bird. The colour is confined to the central pigmented 

 patch and is there exceedingly bright. The barbs are con- 

 tinued beyond the metallic region, but are then without 

 barbules. The figure at the side is a section through the 

 barb to show the method of insertion of the barbules which 

 produces strongly marked ridges on the surface, so that the 

 barbs lie at the bottom of a trough. 



In humming-birds metallic tints occur in both 

 sexes, but are usually more brilliant in the male. 

 They very frequently occur on the general contour- 

 feathers, the colour being then often a bronze-green, 

 which is not sharply confined to a transverse band, 

 but fades away gradually behind. The metallic 



