vii FLIGHT 265 



vertical to its surface and at a certain pace, 

 would be more than double what it would be 

 in the case of a plane one foot square under similar 

 circumstances. Hence small birds get less support 

 from the air than large ones. It is true that, as 

 explained above (see p. 190), the front part of the 

 wing does most of the work during its lightning-like 

 downward movement, and therefore we find that 

 the wings of most of the best flyers have narrow 

 extremities. But during flight the bird's whole under 

 surface forms a parachute, and a gain in area means a 

 disproportionate gain in supporting power, even when 

 we make allowance for the principle just mentioned. 

 Moreover, a short wing necessitates a quick stroke, 

 and much power is lost by the small bird in constantly 

 raising the wing for a fresh effort. A few less 

 important advantages must also be mentioned. The 

 great flyers, even when we take into consideration 

 their greater size, have larger and stronger bones than 

 the best flyers among small birds, and the absence of 

 marrow has prevented an increase in weight that 

 might have been set against the increase in strength. 

 In large birds the coracoids, if we take the average, 

 are directed more outwards than in small birds, a 

 gain in strength without any drawbacks. It is 

 probable that in proportion to their total bulk they 

 require less flight muscle than small birds that 

 resemble them in other respects. Some interesting 

 measurements which go to prove this have been made 

 by Legal and Reichel. In the case of the Pigeon, as 

 I have shown (see p. 212), their figures do not agree 

 with the facts, but in most cases they are, probably, 



