MOTIONS OF OTHER ANIMALS. 361 



the honey of flowers. The vibratory motion of the 

 wings in these instances is only to buoy them up so 

 as to retain their place ; but the instant they are 

 alarmed by the approach of danger, they may be 

 seen to take several long strokes with their wings, 

 and dart off with the rapidity of lightning. This is 

 well illustrated by the motions of birds preparatory 

 to flight, as they may be observed always to take 

 I several deep inspirations, at the same time often rising 

 on tiptoe, and puffing out and balancing their bodies 

 to feel whether they have thrown enough air into 

 their bones and feathers to float them along. Birds 

 of prey {Raptores, Vigors) seem to have the great- 

 est power both of filling their bodies with air and 

 of expelling it again at pleasure. Hence the kestril 

 {Falco tinny nculus) may be seen floating about for 

 a considerable time without moving a wing, or per- 

 haps drawing a breath, till it can hold out no longer, 

 when it flutters its wings rapidly, not for moving 

 to a different place, for it remains stationary, but to 

 recover its decreasing buoyancy by inhaling a fresh 

 supply of air. For the same reason a trout will 

 oscillate its body when losing ground by the rapidity 

 of a stream. The osprey {Falco ossifragus) on the 

 other hand, we have seen, at the Kyles of Bute and 

 elsewhere, shoot down like a thunderbolt from the 

 air into the sea, plunging far into the water upon a 

 fish she had marked for her prey,* — a movement only 

 to be explained by the rapid expulsion of the air 

 which had been the chief agent in keeping her pre- 

 viously afloat in the region of the clouds. Many 

 birds which prey on smaller game have somewhat 

 similar methods of poising and balancing their 

 bodies, of which the water-ouzel (^Cinclus aquaiicus, 



* " Super est Haliaetos," says Pliny, " clarisslma oculorum 

 acie, librans ex alto sese, visoque in mari pisce, praeceps in eum 

 ruens, et discussis aquis, rapiens.'" — Hist. Nat. 



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