62 SEXUAL SELECTION: BIRDS. [Paut II. 



rushing noise," like the falling of a tree* 53 The male alone 

 of one of the Indian trastards (Sypheotides auritus) has its 

 primary wing-feathers greatly acuminated ; and the male 

 of an allied species is known to make a humming noise 

 while courting the female. 54 In a widely-different group 

 of birds, namely the Humming-birds, the males alone of 



certain kinds have either the 

 shafts of their primary wing- 

 feathers broadly dilated, or the 

 webs abruptly excised toward 

 the extremity. The male, for 



Fig. 44.-Primary wing-feather of mstanC p f SelctSphorUS platy- 

 a Hummmg-bird, the Selaspho- j. a 



rus piatycercus (from a sketch cercus, when adult, has the 

 . by Mr. Saivin). Upper figure, fi rs t primary wing-feather (Fig. 



that of male ; lower figure, cor- , v *, . , , . 



responding feather of female. 44 ) excised in this manner. 



While flying from flower to 

 flower he makes " a shrill, almost whistling noise ; " 55 but 

 it did not appear to Mr. Saivin that the noise was inten- 

 tionally made. 



Lastly, in several species of a sub-genus of Pipra or 

 Manakin, the males have their secondary wing-feathers 

 modified, as described by Mr. Sclater, in a still more re- 

 markable manner. In the brilliantly-colored P. deliciosa 

 the first three secondaries are thick-stemmed and curved 

 toward the body ; in the fourth and fifth (Fig. 45, a) the 

 change is greater ; and in the sixth and seventh (6, c) the 

 shaft " is thickened to an extraordinary degree, forming a 

 solid horny lump." The barbs also are greatly changed 

 in shape, in comparison with the corresponding feathers 



53 Mr. Saivin, in « Proc. Zool. Soc' 1867, p. 160. I am much indebted 

 to this distinguished ornithologist for sketches of the feathers of the 

 Chamaepetes, and for other information. 



64 Jerdon, 'Birds of India,' vol. iii. pp. 618, 621. 



55 Gould, 'Introduction to the Trochilidae,' 1861, p. 49. Saivin, 

 'Proc. Zoolog. Soc' 1867, p. 160. 



