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, 1s 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 vibrissee 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 vibrissee. Here again a difficulty meets us; one 
