170 
SEXUAL SELECTION: BIKES. 
Part II. 
as conspicuous to a dangerous degree, the remaining 
twenty-eight being inconspicuous.^'^ Nor is there any 
close relation between a well-pronounced difference in 
colour between the two sexes, and the nature of the 
nest constructed. Thus the male house-sparrow {Passer 
domesticus) differs much from the female, the male 
tree-sparrow (P. montanus) differs hardly at all, and yet 
both build well-concealed nests. The two sexes of the 
common fly-catcher (Muscicapa grisola) can hardly be 
distinguished, whilst the sexes of the pied fly-catcher 
(M, luctuosa) differ considerably, and both build in holes. 
The female blackbird {Turdus merula) differs much, 
the female ring-ouzel (T. torquatus) differs less, 
and the female common thrush {T. musicus) hardly 
at all from their respective males; yet all build open 
nests. On the other hand, the not very distantly- 
allied water-ouzel {Cinclus aquaiicus) builds a domed 
nest, and the sexes differ about as much as in the case 
of the ring-ouzel. The black and red grouse {Tetrao 
tetrix and T. Scoticus) build open nests, in equally well- 
concealed spots, but in the one species the sexes differ 
greatly, and in the other very little. 
Notwithstanding the foregoing objections, I cannot 
doubt, after reading Mr. Wallace’s excellent essay. 
I have consulted, on this subject, Macgillivray’s ^ British Birds,’ 
and though doubts may be entertained in some cases in regard to the 
degree of concealment of the nest, and of the degree of conspicuousness 
of the female, yet the following birds, which all lay their eggs in holes 
or in domed nests, can hardly be considered, according to the above 
standard, as conspicuous : Passer, 2 species ; Sturnus, of which the 
female is considerably less brilliant than the male ; Cinclus ; Motacilla 
boarula (?) ; Erithacus (?) ; Fruticola, 2 sp. ; Saxicola ; Kuticilla, 2 
sp. ; Sylvia, 3 sp. ; Parus, 3 sp. ; Mecistura ; Anorthura ; Certhia ; 
Sitta ; Yunx ; Muscicapa, 2 sp. ; Hirundo, 3 sp. ; and Cypselus. The 
females of the following 12 birds may be considered as conspicuous 
according to the same standard, viz.. Pastor, Motacilla alba, Parus 
major and P. cseruleus, Upupa, Picus, 4 sp., Coracias, Alcedo, and Merops. . 
