Mergus is the genus of the typical mergansers, fish-eating ducks in the seaduck subfamily (Merginae). The Hooded Merganser, often termed Mergus cucullatus, is not of this genus but closely related. The other “aberrant” merganser, the Smew (Mergellus albellus), is phylogenetically closer to goldeneyes (Bucephala). Although they are seaducks, most of the mergansers prefer riverine habitats, with only the Red-breasted Merganser being common at sea. These large fish-eaters typically have black-and-white, brown and/or green hues in their plumage, and most have shomewhat shaggy crests. All have serrated edges to their long and thin bills that help them grip their prey. Along with the Smew and Hooded Merganser, they are therefore often known as “sawbills”. The goldeneyes, on the other hand, feed mainly on mollusks, and therefore have a more typical duck-bill. They are also classified as “divers” because they go completely under-water in looking for food. In other traits, however, the genera Mergus, Lophodytes, Mergellus, and Bucephala are very similar; uniquely among all Anseriformes, they do not have notches at the hind margin of their sternum, but holes surrounded by bone.
Male common mergansers have a greenish-black crested head and upper neck. The lower neck, breast, and underparts are creamy-white with a variable pink wash. They have black backs and upperwing coverts with white scapulars. The bill is red with a blackish culmen and nail. The legs and feet are deep red.
Female common mergansers have a tufted red-brown head that is clearly defined from the lower neck by a clear whitish chin. The back and sides are silver-gray and the breast and belly are white. The bill is red with a blackish culmen and nail. The legs and feet are deep red.
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|wingspan min.:||78||cm||wingspan max.:||94||cm|
|size min.:||58||cm||size max.:||68||cm|
|incubation min.:||30||days||incubation max.:||32||days|
|fledging min.:||60||days||fledging max.:||32||days|
This duck has a wide distribution in boreal and temperate regions of Eurasia and North America. It has also isolated populations in the mountainous regions of the Alps, the Caucasus and Tibet. Two populations inhabit or visit the European Union. One comprises the birds of northern and north-western Europe, wintering mainly in the Baltic Sea and around the North Sea. It amounts to about 200000 individuals, and seems stable. The birds of the British Isles are sedentary. They amount to about 5000-8000 individuals and increased during the last decades. The population of Central Europe (France, Germany) amounts to 3000 individuals. It is also sedentary and seems to be slightly increasing. A very small population is breeding in the Balkan Peninsula. It is estimated at not more than 11-32 breeding pairs, and its trends are unknown
In late August and early September, moulting and breeding waters often deserted as flocks build up on estuaries and shallow parts of some inland lakes. Mass departures not until advent of freezing; thus major movements through Russia and Baltic October and early November. Early arrivals in North Sea countries late October and early November, but no large numbers until December, while numbers build up on Black Sea and Sea of Azov from mid-October to mid-December. Return migration from early March and, apart from stragglers, non-breeding range vacated by mid-April.