If you've been paying attention, you know that corvids (crows, rooks and ravens) are remarkably intelligent birds. Now these feathered geniuses have been given a job: six rooks have been trained to pick up rubbish in the Puy du Fou historical theme park in western France.

Whenever Boubou, Bamboo, Bill, Black, Bricole and Baco deposit a cigarette butt or other small piece of trash in a special receptacle, it dispenses a treat - rewarding the rooks for their efforts.

The idea came from one of the park's falconers, Christophe Gaborit. As part of the falconry show, crows had already been trained to pick up roses and bring them to a princess - so in the 2000s, Gaborit raised and trained two rooks to do the same with rubbish.

The training system is not dissimilar to experimental setups for testing corvid intelligence, in which a dispenser issues a food reward when a crow correctly performs a task.

Earlier this year, we saw research in which a type of "vending machine" was used to teach crows how to tear paper into a specific shape. And 10 years ago, "hacker" Josh Klein built a similar vending machine to reward crows for retrieving lost money. So we know the concept works.

The rooks were deployed for the first time over the weekend, and they'll be working four days a week under close supervision - not for the birds, but to make sure the humans don't deliberately drop rubbish to watch the birds clean it up.

That's because the aim of the rook garbage collectors isn't solely to collect garbage - it's also to get park-goers to think before they litter.

"The purpose of the crows … is to educate the people, to open their minds, to think, 'OK, the birds are able to do something that we are much more able to do than them, so we should do this by ourselves'," park president Nicolas de Villiers told NPR.

"It's a funny way to show the people that you cannot throw the papers everywhere."