FLIGHT 



77 



§ 4. Ordinary Flight 



In ordinary flight the wings begin vertically above the 

 bird's back, and the noise made when they strike together is 

 very familiar in the case of pigeons. The wings move 

 forwards, downwards, backwards, and then upwards again, 

 the up-stroke taking place very quickly and costing the bird 

 very little when it has got fairly a-going. The complete 

 movement of the wing in ordinary flight is complex ; the 

 tip describes for each stroke a sort of figure 8 line, the lower 

 loop of the 8 being much smaller than the upper. 



^^^ 



Fig. 19. — Flight of crested heron. After Marey. In the central 

 bird the wings are vertically above the back. They come forwards, 

 downwards, backwards (first bird to the left), and then up again. 



Marey calculated that the energy expended by a pigeon 

 when taking flight is five times as great as when it has 

 acquired a certain velocity. Professor C. S. Roy wrote in 

 the article " FHght " in Newton's " Dictionary of Birds " : 

 " The bird at starting makes rapid strokes with its wings, 

 which move through a large angle — in the case of the 

 pigeon striking one another above the back at the end of 

 the up-stroke, and nearly touching with their tips at the 

 end of the down-stroke. When velocity has been acquired, 

 the flaps are slower, and the angle which they describe 

 round the shoulder-joint is a very much smaller one. The 

 reason why so much more energy is required to fly when 

 they have little or no initial velocity relative to the air is 

 due to the increased support afforded by the air if the 

 wing-surface which strikes it be at the same time travelling 



