SEXUAL SELECTION 487 



North American grouse, the Tetrao umbellus, when with his 

 tail erect, his ruffs displayed, "he shows off his finery to the 

 females, who lie hid in the neighborhood," drums by rap- 

 idly striking his wings together above his back, according 

 to Mr. E. Haymond, and not, as Audubon thought, by 

 striking them against his sides. The sound thus produced 

 is compared by some to distant thunder, and by others to 

 the quick roll of a drum. The female never drums, "but 

 flies directly to the place where the male is thus engaged." 

 The male of the Kalij -pheasant, in the Himalayas, "often 

 makes a singular drumming noise with his wings, not un- 

 like the sound produced by shaking a stiff piece of cloth." 

 On the west coast of Africa the little black weavers (Plo- 

 ceus?) congregate in a small party on the bushes round a 

 small open space, and sing and glide through the air with 

 quivering wings, "which make a rapid whirring sound like 

 a child's rattle." One bird after another thus performs for 

 hours together, but only during the courting season. At 

 this season, and at no other time, the males of certain 

 night-jars (Oaprimulgus) make a strange booming noise 

 with their wings. The various species of woodpeckers 

 strike a sonorous branch with their beaks, with so rapid 

 a vibratory movement that "the head appears to be in two 

 places at once." The sound thus produced is audible at a 

 considerable distance, but cannot be described; and I feel 

 sure that its source would never be conjectured by any one 

 hearing it for the first time. As this jarring sound is made 

 chiefly during the breeding season, it has been considered 

 as a love-song; but it is perhaps more strictly a love-call. 

 The female, when driven from her nest, has been observed 

 thus to call her mate, who answered in the same manner 

 and soon appeared. Lastly, the male Hoopoe {Upupa 

 ^pops) combines vocal and instrumental music; for during 

 the breeding season this bird, as Mr. Swinhoe observed, 

 first draws in air, and then taps the end of its beak per- 

 pendienlarly down against a stone or the trunk of a tree, 

 "when the breath being forced down the tubular bill pro- 



