"Woodpeckers’ heads are not designed to absorb shock, but rather to deliver a harder and more efficient hit into wood.
Spongy bone between the birds’ brains and beaks was once thought to cushion their brains from the repetitive blows into trees, where they find insects and carve out nests. But new research reveals that the tissue actually helps their heads tap swiftly and deeply with minimal energy use, much like a well-designed hammer..."
From http://www.bluesnews.com/cgi-bin/board.pl?action=viewthread&boardid=1&threadid=249999.
