Red-breasted Merganser (Mergus serrator)

Red-breasted Merganser

[order] ANSERIFORMES | [family] Anatidae | [latin] Mergus serrator | [authority] Linnaeus, 1758 | [UK] Red-breasted Merganser | [FR] Harle huppe | [DE] Mittelsager | [ES] Serreta Mediana | [NL] Middelste Zaagbek


Genus Species subspecies Region Range
Mergus serrator NA, EU widespread


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.

Physical charateristics

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.

Listen to the sound of Red-breasted Merganser

[audio: Merganser.mp3]

Copyright remark: Most sounds derived from xeno-canto

wingspan min.: 67 cm wingspan 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.: 32 days
broods: 1   eggs min.: 7  
      eggs max.: 12  


North America, Eurasia : widespread


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.


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 creche, 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.

Feeding habits

While the young eat mostly aquatic insects, adults primarily eat fish. Crustaceans and other aquatic creatures are also eaten

Video Red-breasted Merganser


copyright: youtube


This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
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 (<120,000 pairs), but was stable between 1970-1990. Although the species declined in Norway, Sweden and Russia during 1990-2000, it was stable across much of its European range, and the large Finnish population increased markedly. The species probably underwent only a small decline overall.
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.
Red-breasted Merganser status Least Concern


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.

Distribution map

Red-breasted Merganser distribution range map

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