CONSIDERATION OF BRITISH BIRDS 115 



4. The absence of conspicuous colouring in 

 preying birds. 



5. The absence of conspicuous colouring in 

 night birds. 



6. The association of open- nesting with 

 conspicuous males. 



7. The post-nuptial change of plumage in 

 the analidse and its absence in other epigamic 

 coloured birds. 



8. The brighter colouring of the female in 

 the Phalaropes and Dotterel. 



9. The presence of cryptic colouring in 

 females and young birds. 



10. The older the bird, the more brightly 

 coloured it is, as in the Gannet. 



11. The female assuming male plumage, when rendered 

 sterile by disease. 



Thus can this hypothesis be applied to any 

 selected material. In birds, it seems that 

 protection of young is the most important 

 factor in causing colour-differentiation in the 

 society ; had insects been chosen, the protec- 

 tion of females would have been seen to be a 

 most important factor in sexual differentiation 

 of colour. 



When material is considered in this way, 

 that is, exhaustively, discourse is confined 

 almost entirely to exceptions. A wrong im- 



