the squirrels seem to have run short on their food supply

the squirrels on the  property seem to have run short on food.  Usually they have tons of hickory nuts in the back woods to eat.  But for whatever reason, they are now gnawing up the large green hickory nuts that are still hanging on the branches.. I can hear them early in the morning when I venture onto the back deck.  Every day it is littered with hard bits of green husk that hurts if you step on them barefoot.  You can see they are not doing very well on gnawing through the husk to get to the inner nut.