If the employees whistled a happy tune while they worked, you'd think for sure you were in a Disney establishment. But at this French theme park, it’s birds that are doing the work, and they're rewarded for their efforts with food.

At Puy du Fou, a historical theme park in Western France, six rooks have been trained to pick up cigarette butts and trash. Rooks are members of the Corvidae family (informally called the crow family), which also includes crows, ravens, jays and magpies. The species are all known for their brains and craftiness.

"The purpose of this adventure is not to clean the park but to educate the people to look after the future of our planet. Thanks to the rooks we tell people that nature itself can teach us to take care of the environment," Nicolas de Villiers, park president, tells MNN.

One of the park's falconers came up with the idea after watching the rooks and noticing that they loved to play with some papers that they had found on the floor, de Villiers says. So the falconer turned it into a game, offering food each time one of the birds brought a piece of trash.

"The rooks are very smart and they like very much to interact with human beings as soon as we pay attention to them," de Villiers says. "We don’t teach them, we just let them understand the game."

A rook deposits trash in a receptacle in exchange for a reward. Puy du Fou

Now, each time a rooks deposit a piece of trash into a box in the park, a nugget of food pops out.

De Villiers says that park visitors enjoy watching the birds.

"We have many big shows at Puy du Fou, all very spectacular. The rooks’ story seems to be a new show, very intimate and truly touching," he says. "People love to watch the rooks playing the game, and they ask lots of questions to the falconer."

The intelligence of crows

Researchers have found that crows use tools, solve puzzles and can even operate vending machines. For one machine, crows received a peanut each time they put a coin in the slot.

In fact, the machine's inventor, Josh Klein, explains in the video above that if a crow can be trained to pick up coins, the possibilities are endless.

"So, what's significant about this to me isn't that we can train crows to pick up peanuts," he says. "Mind you, there's 216 million dollars' worth of change lost every year, but I'm not sure I can depend on that [return on investment] from crows."

"Instead, I think we should look a little bit larger. I think crows can be trained to do other things. For example, why not train them to pick up garbage after stadium events? Or find expensive components from discarded electronics? Or maybe do search and rescue? The main point of all this for me is, we can find mutually beneficial systems for these species. We can find ways to interact with these other species that doesn't involve exterminating them, but involves finding an equilibrium with them that's a useful balance."