the beak of the bullfinch

Bird beaks take the place of hands and fingers when it comes to handling food.  So it makes sense that the beak should be highly and easily adapted to whatever the available food might be.  As it turns out, just a few genes that change the size and curvature of the beak can yield a whole suite of bill shapes, making individual birds more or less better adapted to utilize a particular food source.  This is the basis for the huge variety of bills in the Galapagos finches  — and probably what causes the variation in bill closure and shape in (Red) Crossbills (from yesterday’s post).

Today we saw another finch with an unusual bill — the Bullfinch (so named because it has a pretty massive looking bill for its diminuitive size).

bullfinch-England-

English Bullfinches have unusually short, thick bills that look like they might be good at crushing their food.

Their bill, however, is surprisingly weak, and wouldn’t cause a bruise if it closed on your finger (unlike that of the Crossbill).  Instead, Bullfinches feed by nipping off a berry, seed, capsule, bud, etc., closing the bill against the food so as to shear off the outer coat and use their tongue to glean whatever is inside.  They can even use this harvest strategy to de-shell small snails.

bullfinch-England-

Manipulating food with bill and tongue separates the edible from the inedible.  Perhaps a short, stubby bill is just what is needed to allow the tongue and palate work together.

Although Bullfinches eat mainly seeds, they turn to consuming buds in late winter and early spring during food shortages.  Their extreme success at bud nipping, however, has made them a pest in orchards where they do significant damage to fruit crops by decreasing the number of blossoms.  A single Bullfinch can remove 30 buds per minute on an orchard tree, and the birds move systematically along a branch denuding the buds entirely.

The Hawfinch is a bird on the other end of the crushing strength spectrum from Bullfinch.

hawfinch_rspb.org.uk

Now this is a bird that can crush hard seeds with its massive bill.  In fact, they prefer the seeds of hard nuts, like cherry and plum pits. Photo by Rudo Jurecek for the RSPB.

From short, stubby bill to a large, crushing one — not as difficult genetically speaking as we might think.

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