100 
SEXUAL selection : birds. 
Part II. 
direct and indirect evidence. It is much more difficult 
to decide what qualities determine the choice of the 
females ; but here again we have some direct and in- 
direct evidence that it is to a large extent the external 
attractions of the male, though no doubt his vigour, 
courage, and other mental qualities come into play. 
We will begin with the indirect 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 
courtship being a prolonged affair, and partly on the re- 
iteration of the act of pairing. Thus in Germany and 
Scandinavia the balzens or leks of the Black-cocks, 
last from the middle of March, all through April into 
May. As many as forty or fifty, or even more birds 
congregate at the leks ; and the same place is often fre- 
quented during successive years. The lek of the Caper- 
cailzie lasts from the end of March to the middle or 
even end of May. In North America the partridge 
dances” of the Tetrao phasianellus ‘^last for a month 
or more.” Other kinds of grouse both in North Ame- 
rica and Eastern Siberia ^ follow^ nearly the same habits. 
The fowlers discover the hillocks where the Buffs con- 
gregate by the grass being trampled bare, and this shews 
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 
Bock ; and the natives of New Guinea know the trees 
where from ten to twenty full-plumaged male Birds of 
^ Nordmann describes Bull. Soc. Imp. des Nat. Moscow/ 1861, tom. 
xxxiv. p. 264) the balzen of T'etrao urogalloides in Amur Land. He 
estimated 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, urogallus or the caper- 
cailzie. 
