XIII THE COLOURS OF BIRDS 267 



of the quills, and no specialisation of particular areas. 

 Therefore any tendency to the development of 

 brilliant colouring in the wing-quills would be checked 

 by the resulting injury to flight, and so to the well- 

 being of the species. 



It will be noted that in the following descriptions 

 red and yellow colours are always ascribed to the 

 presence of lipochrome. We have already seen that, 

 according to Gadow, yellow may at times be an 

 optical colour ; in the cases discussed, however, the 

 presence of yellow lipochrome has either been 

 directly proved, or is assumed from the simultaneous 

 occurrence of a red colour, which is always due to 

 lipochrome pigment. The thesis here put forward 

 as to the relation existing between brilliant colouring 

 and variation in feather structure, we propose to 

 develop by a consideration of the colour phenomena 

 in sun-birds, humming-birds, and birds of Paradise. 



Colours of Sun-birds 



The Nectariniidze or sun -birds are a family of 

 mostly small birds often with brilliant colours, 

 inhabiting Africa, and India, and the Malay, where 

 they seem to replace the American humming-birds. 

 Their beauty and their habit of frequenting flowers 

 have caused them to be frequently confounded with 

 true humming-birds, but they are not in any way 

 related to the latter. The bright colours are almost 

 entirely confined to the males, and are by them 

 acquired with extreme slowness, so that birds are 

 said to be not infrequently seen mated while the 

 male is still in a sort of hybrid plumage. Birds in 



