This is the acorn woodpecker. I saw a nature special on it a few years ago and that picture reminded me of it. Here is another image:
The woodpecked DOES indeed drill the hole but they are also the ones who fill the holes. Not sure what this photographer saw but squirrels are known to raid these caches, not supply them.
Of course, wikipedia has the goods:
http://en.wikipedia.org/wiki/Acorn_woodpecker
--Justin