38 SEXUAL SELECTION: BIRDS. [Part II. 



feeding on the seeds of the teazle (Dipsacus) which they 

 can reach with their elongated beaks, while 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 cases, however, especially in that of the quar- 

 relsome 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 afterward 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 ? 

 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 chloropus) "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 engaged for half an hour, until one 

 got hold of the head of the other, which would have been 

 killed had not the observer interfered ; the female all the 

 time looking on as a quiet sj>ectator. 6 The males of an allied 



3 Quoted by Mr. Gould, ' Introduction to the Trochilidae,' 1861, p. 29. 



* Gould, ibid. p. 52. 



6 W. Thompson, ' Nat. Hist, of Jreland : Birds,' vol. ii. 1850, p. 327. 



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