Which goes for just about any largish animal, not just swans. There's a big difference between coming around a bend at 80mph and hitting a deer/sheep/whatever that the driver didn't know was there (and had little chance of stopping before meeting it), and deliberately driving over an animal that was known to be on the line.The issue which hasn't been mentioned is the PR aspect of hitting swans, especially by running trains knowingly past/over them on the track, quite apart from the Crown ownership issue.