Up, down, and all around the bark of trees probing for larvae and beetles. Up goes a woodpecker, down goes a nuthatch. The upside for this pair of foragers: They may get lucky enough to pry open cavities concealing insects and get some grub. The downside? That this particular dead tree trunk might have been already picked over by predecessors. What then? Two hungry birds could meet in the middle and put their heads together. Most likely outcome - 'Next tree, YOU go up and I'LL go down!'