Red-breasted merganser Mergus serrator

The red-breasted merganser is a slim long-bodied diving duck with bright red eyes and shaggy crest of feathers gives the head of both sexes a distinctive profile. This species has a thin, elongated and serrated rusty orange bill. In breeding plumage, the male has a dark green head and crest, a white neck collar and a black-spotted brown (not red) chest, whilst the female has a rusty red head and crest, no collar and a lighter chest without dark spots. In flight, the red-breasted merganser has a prominent white lower wing panel and tends to fly at an angle with their head higher than the feet.


Red-breasted mergansers can be found in both fresh-water and salt-water habitats and are commonly found in shallow bays, inlets or estuaries. Red-breasted mergansers tend to sit low in the water and have a very distinctive elegant profile. They frequently swim with their head partially submerged, diving underwater to catch small fish with their serrated bill. Red-breasted mergansers be seen in small flocks in summer or larger gatherings in winter.

Despite pairing up in winter, the red-breasted merganser breeds quite late in the year, laying large clutches of eggs in May-June. The female incubates the eggs (typically between 7 and 12) which hatch in June-July, whilst the male withdraws to the moulting grounds. Ducklings leave the nest one or two days after hatching and frequently suffer high losses, resulting in only 1-3 ducklings successfully fledging in August.


  • Length 52-62cm
  • Wingspan 66-86cm
  • Weight: 0.95-1.35kg (males heavier than females)
  • Average Lifespan: 7-9 years


Classified in the UK as Green under the Birds of Conservation Concern 4: the Red List for Birds (2015); surveys in some areas of Scotland indicate that the population in North-East Scotland and the Southern Uplands is declining and that the wintering population has also fallen since the mid-1990s.


The red-breasted merganser is a widespread and relatively common breeding species found all year round in coastal waters. They can also be partially migratory, with some birds arriving in Scotland from abroad around February. Autumn migration may start in September, but usually peaks towards the end of October.

When to see

All year round


  • The red-breasted merganser belongs to the ‘sawbills’ because of its long, narrow bill with saw-like ‘teeth’ which are good for gripping fish.
  • Red-breasted mergansers need to eat 15–20 fish per day. Research suggests that they need to dive underwater 250–300 times per day, or forage for 4–5 hours to meet their energy needs.

Common name

Red-breasted merganser

Species name

Mergus serrator

IUCN Red List status

Least concern

When to see in Scotland

All year round

Where to see in Scotland

Scottish Wildlife Trust reserves such as Loch Fleet or Knapdale Forest.

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