206 
SEXUAL SELECTION: BIRDS. 
Part II. 
those with duller plumage and grey legs were the males 
or the young. In an Australian tree-creeper {Climac- 
teris erythrops) the female differs from the male in 
being adorned with beautiful, radiated, rufous mark- 
ings on the throat, the male having this part quite 
plain.” Lastly in an Australian night-jar the female 
always exceeds the male in size and in the brilliance 
of her tints; the males, on the other hand, have two 
'‘white spots on the primaries more conspicuous than 
“ in the female.” 
We thus see that the cases in which female birds are 
more conspicuously coloured than the males, with the 
young in their immature plumage resembling the adult 
males instead of the adult females, as in the previous 
class, are not numerous, though they are distributed in 
various Orders. The amount of difference, also, between 
the sexes is incomparably less than that which frequently 
occurs in the last class ; so that the cause of the differ- 
ence, whatever it may have been, has acted on the fe- 
males in the present class either less energetically or less 
persistently than on the males in the last class. Mr. 
Wallace believes that the males have had their colours 
25 For the Milvago, see ' Zoology of the Voyage of the “ Beagle,” ’ 
Birds, 1841, p. 16. For the Climacteris and night-jar (Eurostopodus), 
see Gould’s ‘ Handbook of the Birds of Australia,’ vol. i. p. 602 and 97. 
The New Zealand shieldrake {Tadorna variegata) offers a quite anoma- 
lous case ; the head of the female is pure white, and her back is redder 
than that of the male ; the head of the male is of a rich dark bronzed 
colour, and his back is clothed with finely pencilled slate-coloured 
feathers, so that he may altogether be considered as the more beautiful 
of the two. He is larger and more pugnacious than the female, and 
does not sit on the eggs. So that in all these respects this species 
comes under our first class of cases ; but Mr. Sclater (‘ Proc. Zool. 
Soc.’ 1866, p. 150) was much surprised to observe that the young of both 
sexes, when about three months old, resembled in their dark heads aud 
necks the adult males, instead of the adult females ; so that it would 
appear in this case that the females ^have been modified, whilst the 
males and the young have retained a former state of plumage. 
