454 THE BIRDS xvi. 13- 



20 . Turbulence is mitigated, however, by the provision of openings, 

 known as slots, which let through part of the air and provide the 

 necessary smooth stream. The spaces that occur between the feathers, 

 especially towards the wing tip, almost certainly function as slots. 

 Probably the arrangement provides a series of such apertures, giving 

 a very efficient high-lift device. Such slots are conspicuous in slow 



Aca'piter 



Fig. 263. Wings built for speed (falcon, Falco) and for manoeuvring 

 (hawk, Accipiter). The former is long and narrow, with relatively 

 large hand feathers. The latter is short and broad, the arm feathers 

 being long and the primaries arranged to make slots. (After Fuertes.) 



fliers (rooks) and especially in those that soar on thermal up-currents 

 (vultures). The feathers of such birds are often individually tapered 

 (Fig. 263). Slots are also found in the wings of large birds that are fast 

 fliers (pheasants), the wing being liable to stall in certain phases of the 

 down strokes. It is possible that the bastard wing acts as a slotting 

 device; indeed, consideration of it played a part in development of the 

 theory of turbulence and slotting. 



The shape of the wing has a very important influence on the air 

 stream. In most birds there is a stiff leading edge and a thinner trailing 

 edge. Nearly all wings are cambered, that is to say, they taper from 

 the leading to the trailing edge, especially in the region of the forearm 



