From the Classics: Harpies

We spread the tables on the greensward ground;
We feed with hunger, and the bowls go round;
When from the mountain-tops, with hideous cry,
And clatt'ring wings, the hungry Harpies fly;
They snatch the meat, defiling all they find,
And, parting, leave a loathsome stench behind.

- Virgil, Aeneid

The Harpies in the Aeneid don't actually attack the humans who intrude upon their domain. They just swoop down, steal all the food, and shit on the banquet table (I'm pretty sure that's what Virgil means by 'defiling'). Even when Aeneas and his companions attack them, the Harpies just kind of sit back and laugh because they can't be hit except by +1 or better weapons ("the fated skin is proof to wounds"). The danger to the travellers is not that the Harpies will kill them, but that they'll starve to death.

This is a cool twist to the monster that is lost when they become directly aggressive. Instead, I want to have the Harpies appear whenever the PCs are trying to eat their meals and snatch up all the food they can. This will work best on an island, in a deep ravine, or some other place where the PCs can't easily come and go. After a few days of no food, the PCs will start to feel weakened from starvation. The Harpies' defences make them difficult (but not outright impossible) to kill. What will the players do in such a situation? Will they turn their energies to exterminating the Harpies? Concoct a plan to eat their food in secret? Or just get what they came for in this location as quickly as they can and then escape?