SEXUAL COLORATION. 270 



individual than with the well-being of the species. The 

 bachelor males (i.e. those, who have not found a mate) are apt 

 tp persecute with their attentions the females while sitting- 

 upon the eggs ; the ideal condition, for monogamous birds, 

 would Ije an exactly equivalent number of males and females ; 

 but this is precisely what we do not get. The bachelor males, 

 therefore, are useless for the species, not only on account of 

 their interference with the females during an important period 

 of their existence, but also because they occupy valuable space 

 and lessen the supplies of food. 



Anything, therefore, tending to lessen the undue preponder- 

 ance of the less useful sex would be, M. Stolznianu thinks r 

 seized upon and perpetuated by natural selection. Hence 

 the gaudy colours, crests and spurs, and pugnacious habits 

 of the males. The bright colours render them visible, not 

 only to each other, but to hawks and other enemies ; the long 

 plumes, such as we find in the birds of paradise, lessen the 

 rapidity of their flight, and cause them to fall an easier prey ; 

 and thus the equilibrium of the species is readjusted. The 

 curious humming bird Loil</iyesia mirnliilis has, in addition to 

 the longer tail feathers, a wing shorter by some millimetres 

 than those of the female ; both these facts of structure tend to 

 lessen the capacity for flight ; a double purpose may be served 

 by this and similar cases ; the birds fall easier victims to 

 predaceous birds, and they are unable to secure so great an 

 abundance of insect food, as their better equipped mates. Here, 

 again, we have two causes which operate in the direction of 

 lowering the numbers of males, and at the same time raising 

 the numbers of the females. 



But not only are comparatively defenceless birds preyed 

 upon by hawks and other stronger birds : they show often, in 

 the breeding season, a pugnacious disposition which leads 



