A THEORY OF ZIBDS' NESTS. 251 



Exceptional Cases confirmatory of the above 

 Explanation. 



There exist a few very curious and anomalous facts 

 in the natural history of birds, which fortunately serve 

 as crucial tests of the truth of this mode of explaining 

 the inequalities of sexual colouration. It has been long 

 known, that in some species the males either assisted in, 

 or wholly performed, the act of incubation. It has also 

 been often noticed, that in certain birds the usual sexual 

 differences were reversed, the male being the more 

 plainly coloured, the female more gay and often larger. 

 I am not, however, aware that these two anomalies had 

 ever been supposed to stand to each other in the rela- 

 tion of cause and effect, till I adduced them in support 

 of my views of the general theory of protective adapta- 

 tion. Yet it is undoubtedly the fact, that in the best 

 known cases in which the female bird is more conspi- 

 cuously coloured than the male, it is either positively 

 ascertained that the latter performs the duties of in- 

 cubation, or there are good reasons for believing such 

 to be the case. The most satisfactory example is that 

 of the Gray Phalarope (Phalaropus fulicarius), the 

 sexes of which are alike in winter, while in summer 

 the female instead of the male takes on a gay and 

 conspicuous nuptial plumage ; but the male performs 

 the duties of incubation, sitting upon the eggs, which 

 are laid upon the bare ground. 



In the Dotterell (Eudromias morinellus) the female 

 is larger and more brightly coloured than the male ; and 



