Both red and gray squirrels eat pine cones. Certain types of birds including the woodpecker and crossbill also eat pine cones. When squirrels eat pine cones, the animals leave behind the cores and stripped scales.
Certain birds also leave behind piles of stripped pine cone scales, but unlike the squirrels' characteristically clean-edged scales, the pine cones left behind by birds are generally rough from being pulled from the cone. Sometimes woodpeckers jam a pine cone into a tree's bark to make the cone easier to eat. The evidence is in the frequent piles of pine cone debris left underneath trees.