SEXUAL CHARACTERS IN BIRDS. 



665 



The subject may be approacliecl from otlier points of view. 

 Many birds are more or less free from enemies on account 

 of possessing powerful weapons of defence — either beaks, 

 talons, wings (e. g., swans), or legs (e. g., cassowaries). Sexual 

 dimorphism should be less commonly found among these birds 

 than among birds in general ; and such is the case, as shown 

 in Table II., only hornbills and toucans being to some extent 



Table II. 



Notes. — Compiled from F. Finn's 'The World's Birds.' 



Secondarj' sex characters classified as before. 



Reference Nos. :— 1 no def. 4, 8, 22, 25, 28, 29, 30, 32, 40, 45, 46 : 2 no def. 10, 26, 

 31, 37, 39, 42, 44 : 3 no def. 11, 21, 38 : 4 no def. 5, 14, 16, 19, 24, 34, 

 41, 49 : 1 def. 1, 2, 6. 9, 13, 17, 18, 35, 36, 43, 48 : 2 def. 3, 7, 12, 15, 20, 

 27, 38, 50 : 3 def. 23, 47. 



exceptional. On referring to Table III., it can be seen that 

 these two families have been correctly described as exhibiting 

 " sometimes sex difference," especially in the case of hoiTibills. 

 As regards toucans, it can be seen that it is chiefly among the 

 smaller and therefore less powerful species that sex dimorphism 

 is found. This, however, is not the case in the hornbills. 

 Although their bills are apparently very powerfid, it is doubt- 

 ful whether they are so in practice ; keepers are of opinion thft 



Notes to Table I., continued. 



In a few cases birds have been placed in two columns, e. g. Pigeons in Terrestrial 

 and Arboreal, Passerine Birds ditto, Divers in Aquatic and Maritime. 



Ducks have been placed under Terrestrial, as they are especially liable to the 

 attacks of carnivorous mammals whilst feeding on dry land or in shallow 

 water ; they are considered in detail elsewhere. 



The bracketed percentages refer to the horizontal lines, the unenclosed percentages 

 to the vertical columns. 



Reference numbers for Table I. : — 



1 Terr. 6, 8, 9, 25, 29, 43, 45, 46 : 2 Terr. 20, 37, 39, 42, 33 : 3 Terr. 11, 

 23 : 4 Terr. 34, 5, 14, 16, 19, 41 : 1 Arb. 4, 28, 30, 48 : 2 Arb. 3, 26, 33, 37, 

 50 : 3 Arb. 23, 38, 47 : 4 Arb. 24, 49, 34, 16 : 1 Aer. 1, 4, 12, 32 : 2 Aer. 15, 

 31 , 40, 44 : 1 Aq. 13, 17 : 1 Ocea. 2, 13, 18, 35, 36 : 2 Ocea. 7 : Nos. 10, 21, 

 22, 27 omitted. 



These numbers refer to the li.st of birds at the end of the paper, and show how 

 they are distributed in tlie tiible: thej' .enable others to criticise \\\e distri- 

 bution. 



