A theme park in France has established a novel and environmentally-friendly way of keeping its grounds free of litter. It has selected and trained six "intelligent" rooks to pick up rubbish and keep the park clean. Rooks are members of the crow family and are up to 47cm in length. The clever birds will be put to work at the Puy du Fou theme park in the west of France. They have been trained to pick up cigarette ends, paper and other things people throw on the ground. The birds pick up the litter and deposit it into a special trash can, which then delivers some bird feed as a reward. The more litter the birds put in the trash can, the more food they get.

The head of the theme park, Nicolas de Villiers, explained the rationale of using the crows to the AFP news agency. He said there were several reasons for deploying the crows. He said: "The goal is not just to clean up, because the visitors are generally careful to keep things clean, but also to demonstrate that nature itself can teach us to take care of the environment." Crows are highly sociable and intelligent birds. Some biologists say they are as smart as a seven-year-old child. Mr De Villiers said: "In an affectionate, supportive atmosphere, they like to communicate with humans and establish a relationship through play." The crows are speedy workers and can fill a bucket with rubbish in less than 45 minutes.