SEXUAL COLOliATION. 279 



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

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

 to persecute with their attentions the females while sitting 

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

 would be 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. Stolzmann thinks, 

 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 Loddigesia mirabilis has, in addition to 

 the longer tail feathers, a wing shorter by some millimetres 

 than those of the female ; both these tacts 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 secnre 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 



