Sexual Dimorphism 
a bright livery at the breeding season; this 
nuptial plumage is by no means invariably con- 
fined to the cock, so that we are brought face to 
face with the fact that some hen birds, that are 
normally inconspicuously coloured, become showy 
and easy to see at the nesting time, that is to say, 
precisely at the season when they would seem to 
be most in need of protection. 
In the great majority of cases of sexual dimor- 
phism among birds the cock is the more showily 
coloured. Now, if it be a matter of life-and- 
death importance to a bird to be protectively 
coloured, we should expect the showily coloured 
cock birds to be far less numerous than the 
dull-plumaged hens, since the former are, ex 
hypothest, exposed to far greater danger than 
the inconspicuous hens. As a matter of fact, 
cock birds in practically all species appear to be 
at least as numerous as the hens. Nor can it be 
said that this is due to their more secretive 
habits. As a general rule, cock birds show 
themselves as readily as the hens ; indeed, in the 
case of the familiar blackbird, the conspicuous 
cock is less retiring in his habits than the more 
sombre hen. It may, perhaps, be thought that 
the greater danger to which the sitting bird is 
exposed accounts for the fact that hens, not- 
withstanding their protective colouration, are not 
more numerous than the cocks. Unfortunately 
for the supposition, in many sexually dimorphic 
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