SEXUAL CHARACTERS IN BIRDS. 



669 



Birds may avoid enemies in other ways ; there is little doubt 

 but that ill-flavour plays a part. Under the heading " Economic 

 Qualities," Finn, in the 'World's Birds,' mentions those birds 

 which form food for man, and this to some extent will separate 

 the well-flavoured from the ill-flavoured. This material is set 

 out in Table YI., which shows that secondary sexual dimoi-phism 

 is especially to be found among table-birds. 



Birds may .also be said to avoid enemies by protective color- 

 ation. However, it is not possible to examine this aspect statis- 

 tically, because protective coloration often forms a part of sex 

 dimorphism, the female presenting this coloration and the male 

 not doing so. This is in itself, however, evidence that sex 

 dimorphism is in some way related to enemies. 



Size. — Upon size must depend to some extent a species' vulner- 

 ability to enemies. Lai-ge birds are only open to the attack of 

 large carnivorous animals, whereas small birds are preyed upon 

 by both small and large. Large birds should, therefore, show 

 less secondary sexual dimorphism than medium-sized birds, and 

 these less than birds of small size. Finn describes the size of 

 birds by comparing them with well-known English ones — for 

 instance, of parrots he says "less than tit to that of an ordinary 

 fowl," of hornbills " from that of a hen turkey to that of a 

 pigeon." Birds thus used in description may be classified 

 into large, medium, and small, and, with this as a measure. 

 Table YII. has been compiled. Parrots would fall, therefore, 

 into all three columns, and hornbills into medium and lai'ge. 



Table VII. 



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



Table of measure for classification : — Large=swan, goose, turkey, "upwards," 

 heron, 3 ft. and above in length : Medium=jay, dove, raven, rook, 

 mallard, partridge, crow, fowl, pheasant, " medium size," pigeon, jackdaw, 

 hen, duck: Small=lark, "very small," thrush, sparrow, blackbird, tit, 

 swallow, quail, starling, linnet, "3 inches." 



Eeference Nos. :— 1 L. 1, 2, 6. 9, 13, 18, 25, 32, 35, 36, 43 : 2 L. 7, 12, 20, 37 : 

 3 L. 11, 23 : 4 L. 5, 14, 16 : 1 M. 1, 2, 4, 8, 13, 17, 18, 22, 25, 28, 29, 32, 35, 

 36, 40, 45, 46, 48 : 2 M. 3, 7, 10, 12, 15, 20, 27, 31, 33, 37, 39, 42, 50 : 

 3 M. 11, 23, 38, 47 : 4 M. 5, 14, 16, 19, 34, 41, 49 : 1 S. 2, 4, 8, 17, 18, 22 

 28, 30, 32, 36, 46 : 2 S. 3, 10, 12, 15, 20, 26, 27, 31. 33, 37, 39, 42, 44, 50 : 

 3 S. 21, 38, 47 : 4 S. 16, 19, 24, 34, 49. 



Secondary sex characters classified as previously. 



Pkoc, Zool. 8oc.— 1915, N'o. XLVI. 46 



