Red-Breasted Merganser

Red-Breasted Merganser

The red-breasted merganser is a medium-sized diving duck that belongs to a group known as sawbills. It is an elegant streamlined bird with a body shape adapted well for swimming, and a long serrated bill that helps it catch and hold on to fish, which make up the majority of its diet. It is similar to the goosander but can be distinguished by its thinner bill, reddish-brown breast, and green crest along the top of its head.

Key facts

Scientific name: Mergus serrator
Status: Resident breeding species and winter visitor

Breeding birds: 2,800 pairs

Wintering birds: 9,000

Conservation status: Green
Length: 52 – 58 cm
Wingspan: 70 – 86 cm
Weight: 900 – 1,350 g


Adult male red-breasted mergansers in breeding plumage have black and white upperparts with a black hind neck, mantle, and back. There is a broad white stripe on each side of the body. Their rump, uppertail-coverts, and tail are grey with pale edges to the feathers which give them a scale-like effect. The tail has a black terminal band.

There is a black and white pattern on the upperwing with broad white wing patches with black-tips. The scapulars are black with white spots.

They have white underparts with reddish-brown mottling on the breast. They have grey flanks with wavy black lines and a conspicuous white collar on the neck.

The head, chin, nape, and upperneck are glossy dark green and they have a dark green crest on the top of the crown and nape. They have slender red bills, and deep red eyes, legs, and webbed feet.

Female red-breasted mergansers are smaller than the males and have grey bodies with dark reddish-brown heads and white chin, throat and breast. There is less white in the upperwing and the scapulars are grey. The bill, eyes, legs, and feet are a duller red.

Males in eclipse plumage are similar to females with a darker mantle and white wing-coverts.

Juveniles resemble females but with duller plumage and a shorter crest.


Red-breasted mergansers breed from April to June in single pairs or in loose colonies. They nest on the ground near water sometimes using rocky crevices. The nest is built by the female and is a concealed shallow depression covered with grass and lined with down plucked from her breast.

Red-breasted mergansers lay 8-10 olive or buff coloured eggs which are incubated by the female. Other birds may lay in the same nest making clutches of up to 24 eggs, which are incubated for 28-35 days.

Chicks are precocial and covered in brown and white down. They leave the nest within 24 hours and fledge 60-65 days after hatching. They are sexually mature at 2 years.


Red-breasted mergansers feed by diving. They eat fish, small crustaceans, worms, amphibians, and insects.

Red-Breasted Merganser

Where to see them

Red-breasted mergansers can be seen all year round but population numbers reach a peak in December and wintering birds return to their breeding grounds in March. They are resident in the north-west of Scotland, England, Wales and parts of Ireland, and during the winter can be found in most coastal areas.


Alan Dalton/xeno-canto

Did you know?

The red-breasted merganser holds the record for the fastest airspeed of a duck while being pursued by an aeroplane, reaching speeds of 100 mph (161 hm/h).

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