Harpies are native to that fiddly little squiggle on the map, there, to the south of that biggish sort of dark thingy, and next to those little upside down arrow thingys – are those mountains? Well, whatever. I don’t know cartography but I know that there’s a place with an arrow on the map marked “Harpies Come From Here.”
Most of them are skittish scavengers. One harpy, however, ended up meeting someone with a special magical gift. That someone was Jerome One-nose, and Jerome’s magical gift was to pick the very best potato from any sack of spuds. Every single time, Jerome could unerringly select the very best potato from countless lumpy brethren, a peerlessly flavorful tater from which could of course be made the very best potato chips. Jerome used to visit the forest where the harpies lived, carrying a sack of potatoes around (he always kept a sack with him, so he could demonstrate his skills whenever needed - it was basically a party trick). During these walks, he would absently toss the very best potato to a particularly starved-looking harpy, thinking nothing of it.
This went on for some time, with the harpy being fed exclusively on a diet of top choice potatoes, until Jerome was accidentally killed in a tragic catapult mishap. The harpy was devastated, deprived of its exclusive diet of prime potatoes, and went berserk, eating everything in sight but never again finding that magically perfect potato. It’s sort of sad, really, except the harpy smells so unpleasant it’s hard to feel sorry for her.