Wings 237 
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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 the 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 
