The adult male in breeding plumage has a reddish-brown mottled breast, white neck collar, green head, and red eyes. The serrate orange bill is very thin. The back is black and white, and the flanks are gray. The female has an overall gray body, reddish-brown head, and reddish eyes. There is no obvious white chin-patch as in the female Common Merganser. The juvenile is similar to the female but has a white bar across its face. Non-breeding adult males appear similar to females as well.
Red-breasted Mergansers are typically found in small flocks, rather than huge rafts. They forage by diving and swimming under water, sometimes in cooperative groups, working schools of fish into shallow water.
Breeding habitat is in the tundra and boreal-forest zones. Breeding occurs on fresh, brackish, and saltwater wetlands and in sheltered bays. During migration and in winter, Red-breasted Mergansers occur mostly on salt water, in coastal bays, estuaries, and other protected coastal areas.
Mergus serrator is a widespread breeder across much of northern Europe, which
accounts for less than a quarter of its global breeding range. Its European breeding
population is relatively small (
This duck inhabits boreal regions – locally also temperate and arctic regions – in North America and Eurasia, from the British Isles to the Bering Street. The birds visiting the European Union belong to a population which breeding area extends from eastern Greenland to Novaya Zemlaya and includes the British Isles, Denmark and Scandinavia. The sub-population of Greenland, Iceland and the British Isles is partly sedentary, partly migratory and wintering in the British Isles. It amounts to about 15000-25000 individuals. The sub-population of northern continental Europe is wintering from the Baltic Sea to Portugal. it amounts to about 125000 individuals. Apart from some extension of its breeding area in the British Isles, this species seems to be quite stable. The birds visiting Greece belong most probably to a more eastern population, the winter quarters of which are centred on the Black Sea. This populations is estimated at 50000 individuals, but its trends are unknown.
While the young eat mostly aquatic insects, adults primarily eat fish. Crustaceans and other aquatic creatures are also eaten
This species has a large range, with an estimated global Extent of Occurrence of 10,000,000 km². It has a large global population estimated to be 510,000-600,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern [conservation status from birdlife.org]
Females first breed at the age of two years. Pairs generally form in late winter and during spring migration, although some evidence of pairing may be evident in the late fall. Breeding is late in the season, and often the young do not fledge until September. The nest is located in a sheltered spot on the ground, usually near water. It is a simple depression lined with vegetation and down. The female lays 7 to 10 eggs, and sometimes lays eggs in the nests of other females. Males usually leave when incubation begins. Incubation is by the female alone and lasts for 28 to 35 days. Within a day or so of hatching, the young follow the female to water where they feed themselves. Often, in areas of high-density nesting, two or more broods will join and form a crèche, with one or more females tending them. Within a few weeks, the females typically abandon the young, who cannot fly until they are about two months old.
Migratory and partially migratory. Breeding population of Iceland partially migratory; some resident, others migrate to Britain and Ireland. Movements of British breeders not fully known, but probably winter around coast not far from breeding areas. Some breeders from Denmark, Norway, Sweden, and northern Germany do not move far, wintering Baltic, coastal Norway (up to extreme north), and Sweden north almost to zone of total icing; others join those migrating from Finland, Poland, Baltic States, and north-west Russia, which winter in force in Baltic and further WSW to Netherlands and Britain, smaller numbers reaching west France. Denmark and Baltic Germany constitute main north and west European wintering area.
males leave nesting areas early June, and, with immatures, moult in small coastal or near-coastal groups, sometimes at considerable distances from breeding places, reaching peak numbers mid-July. Autumn migration may begin September, but final departures from most northern breeding areas not until mid- or late October when peak movement through Baltic and to Black Sea region. As with other diving ducks, tendency for females and young to move earlier and further than males. Spring return may begin late February; arrives April in Baltic breeding range, later (dependent on thaw) further north and east.
- spanwidth min.: 67 cm
- spanwidth max.: 82 cm
- size min.: 52 cm
- size max.: 58 cm
- incubation min.: 31 days
- incubation max.: 32 days
- fledging min.: 60 days
- fledging max.: 65 days
- broods 1
- eggs min.: 7
- eggs max.: 12
- Conservation Status