Thursday, 13 September 2007

Woodpecker signs: nuts

This photo shows a hazelnut wedged in a tree-crevice. This anvil was used by a Great Spotted Woodpecker in Budapest, Hungary (Szabolcs Kókay). Woodpeckers open nuts by pecking the hard shell until it shatters. Syrian and Great Spotted Woodpeckers regularly feed on nuts. They do not seem to be able to make neat holes in nutshells as rodents do. It takes numerous pecks to break open a shell, depending upon which kind of nut is being dealt with. Hazelnuts take longer to break open than, for example, walnuts. Unopened but tried nuts are dotted with peck marks rather than the gnawing marks made by the teeth of rodents. The sizes and shapes of the beak tips of birds that feed on nuts differ. Although it is not always clear these are sometimes diagnostic. The marks left on nuts by woodpeckers are dagger or chisel-shaped (vertical) whereas those left by Nuthatches Sitta europaea are crescent-shaped (horizontal). The chisel shape of woodpecker beaks is ideal for splitting nutshells as nuts split most easily along vertical fault lines. Woodpeckers have learned to exploit this. Nuts are always placed in the anvil downwards and pecked at lengthways in a line until they crack. Nuthatches never work a line to open a nut but rather chisel a round hole like a rodent does.

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