Crows, capable of complex thought and skilled problem solvers, can also make and use tools. Now, several projects aim to enlist crows and other wild creatures as volunteers to keep the environment tidy. A Dutch company, Crowded Cities, has a device called the CrowBar that trains birds to collect discarded cigarette butts in exchange for food, creating a low-cost solution to a problem that is labor-intensive for humans.

The machine presents a piece of food next to a cigarette butt on a platform, training the crow to expect food there. Then it starts dispensing the food only after the crow arrives, teaching the crow how the machine operates. Next, it presents only the cigarette butt, with no food. The crow starts looking around for the food and accidentally knocks the butt in, which releases a treat. The last step is to scatter a few cigarette butts on the ground around the CrowBar. When the training is complete, the crow will start collecting butts from the surrounding area and bringing them to the machine for a reward.