A flock of feathered friends are cleaning up parklands in France.

Specifically, a team of six rooks has been trained by staff at the Puy du Fou historical theme park, located in the western Vendee region, to retrieve cigarette butts and other small rubbish in exchange for food, reported the Guardian.

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“The goal is not just to clear up, because the visitors are generally careful to keep things clean,” but also to show that “nature itself can teach us to take care of the environment,” said Nicolas de Villiers, a custodian of Puy du Fou park.

Rooks, a member of the crow family, are considered “particularly intelligent,” noted Villiers, and under the right circumstances the birds “like to communicate with humans and establish a relationship through play.”

To encourage this behavior, the park has installed a small box that delivers a nugget of bird food each time one of the rooks deposits retrieved trash, Agence France-Presse first reported.

This is not the first time that crows have been praised for their intelligence, noted the BBC.

Earlier this year, scientists created a vending machine that required a particular size of paper token to release a treat, and found that not only could crows remember the correct size of paper, but they would trim down larger pieces in order to fit into the machine, an earlier report stated.