If you haven’t heard, it’s time you did. The Swedish city of Södertälje, close to Stockholm, is embarking on an experiment. It will slash its street-cleaning costs by employing crows trained to pick up cigarette butts. No, I’m not blowing smoke. Cigarette butts make up 62 per cent of all street litter in conscientious Sweden. Södertälje spends 20 million kroner (€1.9 million) on picking butts alone – up to 2 kroner (20 cents) a butt. Trained crows, which will be paid in food, will cut costs by up to 75 per cent. It should work. Birdbrains get bad publicity among us humans. But it’s estimated that New Caledonian crows have the intelligence of seven-year-old humans. Apparently, it’s easier to train crows to pick butts than to train adult humans not to drop them in the street. It’s not the first time that crows have attracted global attention for their intelligence. Three decades ago, a BBC documentary (and, since then, countless YouTube videos) showed them cracking walnuts at the traffic lights. While the lights were red, the birds dropped a nut in front of a wheel. The lights went green, the cars set off and crushed the nuts beneath their wheels. When lights went red again, the...