The Finch’s Bill
The beak of a finch is modified internally for shelling seeds. Each seed is wedged in groove on the side of
the palate and crushed by raising the lower jaw onto it. The husk Is peeled off with the aid of the tongue and discarded, while the kernel is swallowed. The cardueline finches can extract seeds from the seed-heads of plants. Species differing the size of seeds they prefer, and in the types of seed-head they can best exploit, corresponding with differences in the size and shape of their bills. Hawfinches have big powerful bills for crushing large hard tree fruits, such as cherry stones.
Goldfinches have long tweezers-like bills for probing into thistles, and other composite plants: they are the only species able to eat the seeds of teasel, which lie at the bottom of long. Spiked tubes. The male European goldfinch has a slightly longer beak and can reach teasel seeds more easily than the female. Which in consequence rarely feeds from this plant? Siskin’s also have tweezers-like bills. And feed largely from seeds in small cones. Such as alder.
Bullfinches and Pine grosbeaks have rounded bills adapted for eating buds and berries, the bullfinch in general taking smaller items than the grosbeaks. The crossbills use their crossed mandibles to help them extract seeds from hard closed cones. The three species in Europe have different-sized bills and feed primarily from different conifers: the slender-billed Two-barred crossbill eats seeds mainly from the small soft cones of larch, the medium-billed Common crossbill feeds mainly from the medium cones of spruce, and the large heavy-billed Parrot crossbill mainly from large hard cones of pine.