96 SEXUAL SELECTION: BIRDS. [Part XL 



rect and iiulircct evidence. It is much more ditlicult to 

 decide wliat qualities determine the choice of the females ; 

 but here again we have some direct and indirect evidence 

 that it is to a large extent the external attractions of the 

 male, though no doubt his vigor, courage, and other men- 

 tal (lualitics, come into play. "We will begin with the in- 

 ilirect evidence. 



Length of Courtship. — The lengthened period during 

 which both sexes of certain birds meet day after day at 

 an appointed place, probably depends partly on the court- 

 ship being a prolonged atlair, and partly on the reitera- 

 tion of the act of pairing. Thus in Germany and Scandi- 

 navia the balzens or leks of the Blackcocks last from the 

 middle of March, all through April into May. As many 

 as forty or fifty, or even more, birds congregate at the 

 k'ks ; and the same place is often frequented during suc- 

 cessive years. The lek of the Capercailzie lasts from the 

 end of March to the middle or even end of May. In 

 North America " the partridge-dances " of the Tetrao 

 phasianelltcs " last for a month or more." Other kinds of 

 grouse both in North America and Eastern Siberia' fol- 

 low nearly the same habits. The fowlers discover the 

 hillocks where the Ruffs congregate by the grass being 

 trampled bare, and this shows that the same spot is long 

 frequented. The Indians of Guiana are well acquainted 

 with the cleared arenas, where they expect to find the 

 beautiful Cocks of the Rock; and the natives of New 

 Guinea know the trees where from ten to twenty full-])lu- 

 maged male Birds of Paradise congregate. In this latter 



' Nordraann describes (' Bull. Soc. Imp. des Xat. Moscow,' 18(51, tome 

 xxxiv. p. 264) the balzen of Tetrao urogalloidcs iu Amur Land. He esti- 

 mated the number of assembled males at above a hundred, the females, 

 which lie hid in the surrounding bushes, not being counted. The noises 

 uttered differ from those of the T. urogaJhis or the capercailzie. 



