G7« 



1)R. J. C. MOTTRAM ON SECOXBARY 



mentioned tliat the Australian warblers (Malui'idfie) present great 

 sex difference (the males are amongst the most brilliant of birds), 

 and yet they make closed nests. They are small defenceless 

 birds, and so they not only form exceiations to the open-nesting 

 theory, but support the correlation under consideration. 



Table XV. (Nesting-habits.) 



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



Honey-guides, parasitic; the rest, nesting-habits not mentioned. 

 Reference Nos. to middle column, the others are to be seen in Table.s XIII. and 

 XIV. 1 open and closed, 2, 32, 36 : 2 open and closed, 10, 15, 44 : 4 open 

 and closed, 14, 19, 34. Percentages to right of figures = horizontal pei-- 

 centages, percentages below = vertical percentages. 



Further, it is noteworthy that Honey-guides (Indicatoridfe) 

 sometimes present sexual diflerences (Finn), and yet these birds 

 axe parasitic. This exception is important because it shows that 

 the rearing of young as well as the open-nesting habits cannot 

 account — in this case, at any i-ate — for secondary sexual di- 

 morphism. 



The Aphrodisiac Theory. — Those who believe in the necessity 

 for an aphi-odisiac (bright feathers, sexual display, and song) 

 must assume coyness on the part of the female. Little, if any, 

 attempt, however, is made to establish this important sexual 

 difference — a coy female and an impudent male. There does 

 not appear to be any leason wh}^ the females of birds especially 

 subject to the attack of enemies should be especially coy, or that 

 among birds not especially subject to attack the females should 

 not require a powerful stimulant. 



The Cataholism T'Jieory (Vroi. Geddes and Thomson, 'Evolu- 

 tion of Sex,' 1889). — The secondary sexual structures found in the 

 males are consideied to be due to a katabolic constitution, and 

 their absence in the female due to an anabolic tendency. 



No attempt is made to explain the distribution of secondar}' 

 sexual characters among birds on this theory, or to give a reason 



