I encountered this evidence of a nut thief on our boardwalk - those are MY hazelnuts!
Those pesky gray squirrels. I was 'saving' those for myself, but picking them whilst green seemed a little premature. They'd be indigestible, I figured. Not so for the squirrels - they've managed to break through the shells of my beaked hazelnuts, and hollow out the 'meat' for themselves.