FROM London Birds ' to ' Marsh Birds ' is not a considerable step, the obvious link being the sea-gull that breeds on the marsh and feeds on the town. Other birds covered in this further talk in Mr. Massingham's series are the ' Bittern with his boom, the bearded Tit (of whose fairy harp and lamentable history Mr. Massingham will have interesting things to say); the Sand Martin, and the Starling, whose autumnal ' hostings ' have long puzzled ornithologists.