COLOURATION OF BIRDS AND THEIR EGGS. 169 



So also with the birds themselves, it is difficult to see why the 

 cock Song-Thrush should be protectively coloured, but the cock 

 Blackbird conspicuous on account of his intense black plumage. 

 I am not aware that the former assists in incubating the eggs, 

 and that the latter does not perform any such office. It is obvious 

 that certain birds have little or no need of protectively coloured 

 plumage. Some are naturally protected by their size and strength, 

 e.g. the Swan ; others by size combined with gregarious habits, 

 as the Eook and Heron ; or, by these defences combined with 

 great powers of diving, as the Cormorant and Guillemot. Birds, 

 except very small ones, which nest in holes can dispense with 

 protective colours. It may fairly be said that the position and 

 structure of the nests regulate the colouring of the birds them- 

 selves as well as their eggs, and that wherever there is no special 

 need for sombre shades of plumage, conspicuous or bright hues 

 prevail. 



I. Of birds which make open nests, either (a) both sexes are 

 protectively coloured; or (b) the hen so coloured and the cock 

 more showy. 



It will be readily seen that small birds, and birds frequenting 

 very exposed places, specially need protection. It is such birds 

 which have both sexes protectively coloured, e.g. Song-Thrush 

 Hedge-Sparrow, Lark, smaller Game-birds, Bails, Plovers, Sand- 

 pipers. Certain species of the last-named group have the sexes 

 different. 



That the hen should be sombre but the cock conspicuous is 

 not surprising in large birds, such as Ducks and the larger 

 Game-birds. But in a less degree it holds good also in the 

 case of many small birds, such as the Blackbird, Blackcap, Wag- 

 tails, some of the Finches, and Buntings ; but in all these (except 

 the Blackbird) the colouring of the upper parts tends to har- 

 monize with their surroundings. 



Among the Plovers and Sandpipers the Dotterel {Charadrius 

 morinellus) and Phalarope (Phalaropus hyperboreus) may be men- 

 tioned as exceptional, for with them the female is more brightly 

 coloured than the male. The explanation lies in the fact that 

 these males perform the duties of incubation. 



Most sea-birds are equally showily coloured in both sexes. 

 They nearly all have pure white under parts, which strongly 



