FORM AND HABIT: THE WING. 23 



me take you finally to the poultry yard, where in the 

 waddling Duck you will see an undeniable instance of 

 degeneration. 



As the seat of sexual characters the wing is some- 

 times most singularly developed or adorned. The males 

 of the Argus Pheasant and Pennant-winged Nightjar 

 have certain feathers enormously lengthened ; the Stand- 

 ard-bearer has white plumes growing from the wing ; and 

 there are many other cases in which the wing presents sex- 

 ual characters, not alone through display, but also by 

 use as a musical organ. I do not refer to the whistling 

 sound made by the wings of flying Doves or Ducks, or 

 the humming of Hummingbirds, but to sounds volun- 

 tarily produced by birds, and evidently designed to an- 

 swer the purpose of song. 



A simple form of this kind of " music " is shown by 

 the cock in clapping his wings before crowing, in the 

 "drumming" of Grouse, or in the " booming " of Night- 

 hawks, as with wings set they dive from a height earth- 

 ward. The male Cassique (Ostinops) of South America, 

 after giving voice to notes which sound like those pro- 

 duced by chafing trees in a gale, leans far forward, 

 spreads and raises his large orange and black tail, then 

 vigorously claps his wings together over his back, mak- 

 ing a noise which so resembles the cracking of branches 

 that one imagines the birds learned this singular per- 

 formance during a gale. 



The birds mentioned thus far have no especial wing 

 structure beyond rather stiffened feathers; but in the 

 Woodcock, some Paradise -birds and Flycatchers, Guans, 

 Pipras, and other tropical birds, certain wing-feathers 

 are singularly modified as musical instruments. Some- 

 times the outer primaries are so narrowed that little but 

 the shaft or midrib is left, as in both sexes of the Wood- 

 cock, when the rapid wing-strokes are accompanied by a 



