Some types of
woodpecker, such as the Pileated Woodpecker (dryocopus pileatus), actually do dig
further than just the
surface of trees. They use their bill to
drill deep into the
tree, often old pine trees, in order to carve out a cavity in which to build their
nest. You may also see them tapping at and removing the
bark around the entrance in order to make
sap flow across the surface. This is to make it harder for
predators to cling on while attacking the nest.
Some types of woodpecker also use their bill to hammer on trees as part of their courtship rituals and all use it to dig for food, such as termites.
To summarise, woodpeckers are craftsmen themselves, they carve out homes for their families and select mates on the quality of their carpentry.