672 



DR. J. C. MOTTRAM ON SECONDARY 



Song, another secondary sexual character, was also treated in 

 the same way, and clearly substantiates the former finding, as is 

 shown in Table XI. 



Table XI. 



Note. — Compiled from H. Seebolim's ' Turdidas.' 



?=No note was made with reference to song. No song includes such descriptions as 



"song not known," "bird is silent," "never heard." 



Birds may be looked at with advantage from another point of 

 view. In Table XII. they are classified according to their sexual 

 dimorphism without reference to any other factor. Examin- 

 ation of this table (XII.) shows that among birds presenting no 

 sexual difl'erence (column 1) 10/22nds 45 per cent, are relatively 

 free from enemies ; among birds usually presenting no sex dif- 

 ference (column 2) 5/15ths 33 per cent. ; among birds sometimes 

 presenting sex diflerence 2/5ths 40 per cent., and among birds 

 usually presenting sex difference 0/8ths per cent, are free from 

 enemies. 



Table XII. 



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



Numbers at column headings refer to secondary sex characters as before. N.L.=not 

 liable to attack ; L. liable to attack ; % = percentages of birds not especially 

 liable to the attack of enemies. This is a synopsis of the previous table. 

 Reference Nos —1 N.L. 1, 2, 6, 13, 17, 18, 32, 35, 36, 43 : 1 L. 4, 8, 9, 22, 25, 28, 

 29 30 40 45 46, 48 : 2 N.L. 7, 12, 20, 33, 44 : 2 L. 3, 10, 15, 26, 27, 31, 

 37' 39' 42,' 50 : 3 N.L. 23, 47 : 3 L. 11, 21, 38 : 4 L. 5, 14, 16, 19, 24, 34, 

 41' 49! 



Thus it is clear that birds liable to attack more commonly 

 present secondary sexual difi'erences than birds not so liable to 

 attack. If, instead of considering birds from abroad standpoint, 

 a TOore detailed analysis be xiiade, the same result is arrived at. In 



