Notes on Sexual Selection.



211



V. Female like male, but with brighter “ soft parts ” ; Asiatic

Jabiru ( Mycteria australis ); some Cockatoos ( Cacatua

leadbeateri , sulphurea and roseicapilld). In these the iris

is brighter in the female.


No female bird possesses special structural decorations or

weapons, so that for some reason or other evolution in the direc¬

tion of female superiority does not (? cannot) proceed very far.


Sex-similarity, on the other hand, is of two kinds:—


A. Both sexes may be dull, or have plumage of a type which


is feminine in allied species which show masculine

superiority ; e.g. Corn-bunting ( Emberiza miliaria') ;

Australian Wild Duck ( Anas superciliosa ). An extremely

common case, applying often to whole families.


B. Both sexes may be bright, or have plumage which is


masculine in species showing masculine superiority ; e.g.

Goldfinch ( Carduelis caiduelis) ; Superb Tanager (Calliste

fastuosa) ; Chilian Wigeon ( Alareca sibilatrix ). A com¬

paratively rare case, but still sometimes found in whole

groups.


C. Both sexes may have special weapons, e.g. Cassowaries


( Casuarius) ; Spur-winged Geese (Fleet ropier us) and all

Spur-winged birds of any sort.


D. Both sexes may have special structural decorations—


special by comparison with their young or their nearest

allies ; e.g. Guinea-fowls (Numidinae), especially the

hackled Vulturine (Acryllium vulturinum).


E. Both sexes may be alike, but have different voices, e.g.


many ducks, whether of dull or bright plumage.


As in the case of sexually differing birds, the decorations

of similar-sexed birds may be seasonal, a most striking case

being the “ Osprey” plumes worn by breeding Egrets (Herodias),

and the ruff of the Crested Grebe ( Podicipes crislatus).


There is one case of a seasonally developed weapon in the

Pheasant-tailed Ja^anas (Hydiophasianus chirurgus) in wdiicli the

wing-spurs are only developed in the breeding-season.


There are, of course, plenty of cases wdiicli connect various

classes :— e.g. in the Blue Tit (Pams cczruleus) and Gouldian

Finch (Poephila gouldice), the sexes are both richly coloured, yet



