PERCHING BIRDS. 173 



used. White's idea that the bird captures insects with 

 its foot, and that the toothed claw is to give it a firmer 

 grasp, is a pretty one, though I do not think this is its 

 usual practice ; if it is, we might suppose that a careful 

 observer could not fail in time to mark the action of the 

 leg as it struck at its prey; but during many years' 

 attentive observation I have failed in seeing it used in 

 this way. Bishop Stanley is of White's opinion, and 

 says that its singular habit of " dropping or tumbling 

 over as if shot " is in consequence of the bird losing its 

 balance as it puts its food into its mouth with its foot. 

 I believe, however, an examination of the claw itself 

 would be against White's theory. It is slightly flattened 

 and curved outwards, and it is the inner or convex edge 

 that is pectinated, not the under side, which would 

 make it the most effective instrument for grasping. 

 Then the kestrel, which is known to catch cockchafers 

 with its foot, should also have a serrated claw, but it is 

 entirely devoid of anything of the kind. 



Alexander Wilson's opinion is that in the American 

 species it is employed for the purpose of freeing the 

 plumage of the head from vermin, that, he says, " being 

 the principal and almost only part so infested in all 

 birds ; " but why, then, are not all birds furnished with 

 a similar comb ? 



There is yet a third theory viz., that the said comb 

 is used to straighten the vibrissse with which the bill is 

 furnished, and which may get clogged or bent in use. 

 The singular tumbling over during flight, which White 

 and Bishop Stanley think is due to the bird losing its 

 balance whilst putting an insect into its mouth, might 

 with equal reason be attributed to the action of combing 

 out the vibrissse. Here again a difficulty meets us ; one 



