A Dutch start-up company called Entitled Crowded Cities, has come up with an ingenious idea to get our feathered friends to help clean up urban areas. It is estimated that there are 4.5 trillion (4,500,000,000,000!) non-biodegradable cigarette filters littering the cities of the world. This company is training crows to recognize and pick up cigarette butts from streets and green areas in return for a reward. When the crows drop thelitter into a specially designed 'Crowbar', a camera examines the item to confirm that it is actually a cigarette butt. The birds are thengiven somefood which reinforcestheir motivation to keep doing it.