Wings 337 



instance of a condition where an important organ is actu- 

 ally in process of losing its primary function, and in so 

 doing becomes a source of danger to the bird. 



In the waters of the sea near the Falkland Islands is 

 a duck known as the Steamer or Side-wheel Duck. The 

 young birds of this species are good flyers and whistle 

 through the air on strong pinions. But maturity, instead 

 of bringing, as in most birds, a fully perfected power of 

 flight, takes from them what they have, and after the first 

 moult they are helpless to rise above the great waves 

 of their haunts. However, this duck finds another use 

 for its wings, and the stiffness which forbids their being 

 used in the air makes of them bladed paddles which are 

 all the better for their lack of flying power, and with wings 

 and feet these birds make remarkable speed through the 

 water "twelve or fifteen miles an hour" and they are 

 thus able to live out their lives in safety. Thus the study 

 of the flight of these birds carries us a step farther than 

 the tinamou, with the all-important difference that, in this 

 case, loss of the primary function is compensated by a 

 direct adaptation of the wing to tlie new conditions of life. 



In the ostriches and their near allies the extreme reduc- 

 tion of wings is to be found, and yet in the true ostriches 

 and rheas the great expanse of soft feathers is a consid- 

 erable help to the birds when running at full speed, acting 

 as a sail or aeroplane to assist in the onward motion. 

 But the contrast between a loose, open-work feather from 

 the wing of one of these birds and a compact, firmly vaned 

 plume from a condor's wing is very striking. The casso- 

 wary has from four to six flight-feathers, but, far from 



