1256 Birds. 



the bird to sink or submerge itself, it ought to have in its power to 

 contract itself to such a degree that it would only displace a volume 

 of water less than its own weight, let us say 1| pound ; but I am per- 

 suaded that this is not possible, as the contraction which would expel 

 a cubic inch of air from its body* would not of itself be sufficient to 

 cause such an effect. 



Mr. Slaney speaks also of the use air-cells may be of, to birds of 

 prey ; I am fully persuaded that they are greatly conducive to their 

 buoyancy, but I do not believe that they have anything to do (in the 

 manner that gentleman intimates) with the sudden swoops these birds 

 make, which are I think produced by a sudden and powerful move- 

 ment, giving the impulse (obliquely downwards) and followed by a 

 momentary semi-expanded state of the wings (serving as a parachute 

 to prevent their too rapid fall); to this must be added the motions of 

 the legs balancing the centre of gravity, and the expanding, closing, 

 and turning of the sail in various degrees, regulating and directing the 

 flight. 



The air-cells of birds of prey are a beautiful provision of nature, as 

 in augmenting their buoyancy, it impedes greatly the extraordinary 

 velocity with which solid bodies are known to fall through the atmos- 

 phere (by the laws of gravitation), and which would cause an eagle 

 pouncing suddenly on its prey from a height of from between 2000 

 and 3000 feet to be dashed to pieces, without its having power to save 

 itself, if it were deprived of these cells. 



I finish here this dissertation, which I fear has been too long, and 

 return to my birds, concluding the migratory ones of the present 

 group by 



c. Water-birds, which at the time of their migration through Bel- 

 gium are to be found indiscriminately along our coast, and in the in- 

 terior, on rivers, lakes, ponds, marshes, &c. 



Ringed Plover, Charadrins Hiaticula. Not uncommon. It runs 

 very fast on the sands of the sea-shore ; taking but short flights when 

 driven up. Its note is a shrill whistle. Seen in small flocks or in 

 couples, and never nestles here, though it does so commonly on the 

 banks of the Moselle. 



* I do not suppose a moorhen can expel more than that quantity of air at each 

 expiration, as man when breathing only throws out about twenty times that sum. 



