The Mergansers very rarely come on land; they are exclusively aquatic, and frequent rivers, lakes, and pools, preferring them to estuaries; but they may be seen in summer fishing in the sea-lochs of Scotland. The Latins gave them the name of _Mergus_ in consequence of their habit of swimming with the body submerged--the head only appearing above the surface of the water. These birds feed on fish, of which they destroy an immense number. They also commit serious depredations on the spawning beds. They are able to accumulate a large quantity of air in the trachea, and can therefore remain some time under water without breathing. They take advantage of this for diving to the bottom to seek their prey, and they will often travel to a considerable distance before they appear again on the surface. The activity they display in pursuit of their prey is very great; for, in order to accelerate their speed in swimming, they make use of their wings as well as of their feet. The Merganser is in the habit of swallowing fish head first; consequently, it often happens that the remainder of the body of their prey is too bulky to be easily gorged; they are, however, very far from wishing to get rid of this temporary inconvenience, but wait till it becomes gradually absorbed. Sometimes the digestion of the fish's head has already commenced in the bird's stomach whilst the tail is still projecting from its bill. The flight of the Merganser is rapid and prolonged, without reaching any great elevation. Their gait on land is awkward and tottering. They generally inhabit temperate regions during the winter, and in spring return to the high latitudes of both hemispheres, which are their breeding-places. They lay from eight to fourteen whitish-coloured eggs, either on the shore between two large stones, or in thickets of grass on the edge of lakes and rivers: occasionally a hollow in a tree is selected; but it is invariably near water. Their nest is composed of dry grass, sedges, fibrous roots, and other similar materials, with a lining of down plucked from the breast. The Merganser is a regular visitor, in winter, to our coasts and inland lakes. It breeds in North Uist and others of the Outer Hebrides. Its flesh is unedible except when young. THE SMEW. ENGLISH SYNONYMS.--Smew: Montagu, Selby, Jenyns. Pied Smew: McGillivray. White Nun: Selby. Pied Diver, Vane Widgeon. LATIN SYNONYMS.--_Mergus albellus_: Linn., Latham, Jenyns, Bonaparte, McGillivray. _Mergus minutus_: Young, Linn., Latham. FRENCH SYNONYMS.--_Harle Piette_: Temminck. _Harle Huppé_: Buffon.