Sandwich terns eat lesser sandeel, herring, sprat and greater sandeel. They catch these fish by hovering above the water surface. When prey comes into view, they shoot downwards from a great height. It's not so strange that they catch herring and sprat in this way. The fish live in the upper water layer and can be easily caught from the air. However, lesser and greater sandeel live close to the bottom of the sea. The terns can only catch these fish when they are forced to the upper layers due to strong currents.