It is very different, however, with the water-birds, for they have not only kept the power of flight, but have gained the double advantage of also floating safely on the water. Look at our common wild duck. We might have taken him just as well as the sparrow for our type of a bird, and yet while the sparrow leads a land life in the trees, the duck’s home is on the water, and many of his relations live cradled on the open ocean. See his broad boat-like body which floats without any effort of his; notice how closely it is covered with short thickly-grown feathers, which protect him from the chilly water, while he keeps them well-oiled with his beak, from an oil-gland which all flying birds have at the base of the tail. Watch how he swims, drawing his webbed foot together as he brings it forward, and spreading it like a fan to strike the water as he drives it back. Then, as he feeds, watch him gobbling in the mud and then shaking his head as he throws his beak up in the air. For he, like all ducks and geese, has a set of thin horny plates inside his broad bill, and they sift the mud, while the tender tooth-like edges of his beak and tongue feel out the suitable morsels. All this time he is a water animal, but when he rises and flies he is also master of the air, for his strong wings carry him stoutly, so that he can migrate from one pool to another; or in winter, when the pools are frozen, to the open sea. He is by no means the best flyer of his family, and yet he is spread over Europe and North America, and even as far east as Japan, while his ocean-loving cousin, the eider-duck, lines her nest and lays her eggs high up in Arctic latitudes, and dives and swims in the open ocean. So too his relations, the wild swans and geese which wander in the lakes and swamps of Lapland, Siberia, and Hudson’s Bay, feeding on water-weeds, worms, and slugs, build their nests in the summer in the far north, and then fly thousands of miles southwards to their winter homes, their strong wings whirring in the air as they go.