MERGANSER, a word due to C. Gesner (Hist, animalium iii. 129) in 1555, and for long used in English as the general name for a group of fish-eating ducks possessing great diving powers, and forming the genus Mergus of Linnaeus, now regarded by ornithologists as a'sub-family, Merginae, of the family Anatidae. The mergansers have a long, narrow bill, with a small but evident hook at the tip, and the edges of both mandibles beset by numerous horny denticulations, whence in English the name of " saw-bill " is frequently applied to them. Otherwise their structure does not much depart from the Anatine or Fuliguline type. All the species bear a more or less developed crest or tuft on the head. Three of them, Mergus merganser or castor, M. serralor, and M . albellus, are found over the northern parts of the Old World, and of these the first two also inhabit North America, which has besides a fourth species, M. cucullatus, said to have occasionally visited Britain. M. merganser, commonly known as the goosander, is the largest species, being nearly as big as the smaller geese, and the adult male in breedingattire is a very beautiful bird, conspicuous with his dark glossygreen head, rich salmon-coloured breast, and the upper part of the body and wings black and white. This full plumage is not assumed till the second year, and in the meantime, as well as in the post-nuptial dress, the male much resembles the female, having, like her, a reddish-brown head, the upper parts grey and the lower white. In this condition the bird is often known as the " dun diver." This species breeds abundantly in many parts of Scandinavia, Russia, Siberia and North America, and occasionally in Scotland. M . serrator, commonly called the red-breasted merganser, is a somewhat smaller bird; and, while the fully-dressed male wants the delicate hue of the lower parts, he has a gorget of rufous mottled with black, below which is a patch of white feathers, broadly edged with black. Both these species have the bill and feet of a bright reddish-orange, while the much smaller M . albellus, known as the smew, has these parts of a lead colour, and the breeding plumage of the adult male is white, with quaint crescentic markings of black, and the flanks most beautifully verxniculated.
M. cucullatus, the hooded merganser of North America, is in size intermediate between M. albellus and M. senator; the male is easily recognizable by his broad semicircular crest, bearing a fanshaped patch of white, and his elongated subscapulars of white edged with black. The conformation of the trachea in the male of M. merganser, M, senator and M. cucullatus is very like that of the ducks of the genus Clangula, but M. albellus has a less exaggerated development more resembling that of the ordinary Fuligula. 1 From the southern hemisphere two species of Mergus have been described, M. octosetaceus or brasilianus, L. P. Vieillot (N. Diet. d'Hist.naturelle, ed. 2, vol. xiv. p. 222; Gal. des oiseaux, torn. ii. p. 209, pi. 283), inhabiting South America, of which but few specimens have been obtained, having some general resemblance to M . senator, but much more darkly coloured, and M. australis, Hombron and Jacquemont (Ann. sc. not. zoologie, ser. 2, vol. xvi. p. 320; Voy. au Pol Sud, oiseaux, pi. 31, fig. 2), known only by the unique example in the Paris Museum procured by the French Antarctic expedition in the Auckland Islands.
Often associated with the mergansers is the genus Merganella, the so-called torrent-ducks of South America, of which six species have been described; but they possess spiny tails and have their wings armed with a spur. These with Hymenolaemus Malacorhynchus, the blue duck of New Zealand, and Salvadorina waigiuensis of Waigiou are placed in the sub-family Merganettinae. (A. N.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)