40 SEXUAL SELECTION : BIRDS. Part II.' 
am assured by Mr. J. Jenner Weir that the bird- 
catchers can distinguish the males by their slightly 
longer beaks. The flocks of males, as an old and trust- 
worthy bird-catcher asserted, are commonly found feed- 
ing on the seeds of the teazle (Dipsacus) which they 
can reach with their elongated beaks, whilst the females 
more commonly feed on the seeds of the betony or 
Scrophularia. With a slight difference of this nature 
as a foundation, we can see how the beaks of the two 
sexes might be made to differ greatly through natural 
selection. In all these eases, however, especially in 
that of the quarrelsome humming-birds, it is possible 
that the differences in the beaks may have been first 
acquired by the males in relation to their battles, and 
afterwards led to slightly changed habits of life. 
Law of Battle. — Almost all male birds are extremely 
pugnacious, using their beaks, wings, and legs for fighting 
together. We see this every spring with our robins and 
sparrows. The smallest of all birds, namely the hum- 
ming-bird, is one of the most quarrelsome. Mr. Gosse 3 
describes a battle, in which a pair of humming-birds 
seized hold of each other’s beaks, and whirled round 
and round, till they almost fell to the ground ; and M. 
Montes de Oca, in speaking of another genus, says that 
two males rarely meet without a fierce aerial encounter : 
when kept in cages “ their fighting has mostly ended 
“ in the splitting of the tongue of one of the two, which 
“ then surely dies from being unable to feed .” 4 With 
Waders, the males of the common water-hen ( Gallinula 
chlorojpus) “ when pairing, fight violently for the females : 
“ they stand nearly upright in the water and strike 
“ with their feet.” Two were seen to be thus efieaeed 
O O 
3 Quoted by Mr. Gould, 1 Introduction to the Trochilidaj,’ 1861 p. 29 
4 Gould, ibid. p. 52. 
