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Red-breasted Mergansers are medium-sized diving ducks. Their plumage is dimorphic, i.e. males and females are different. Male Red-breasted Mergansers in breeding plumage have a black head with a conspicuous, stringy black crest and a green hue on the sides of the head. The neck has a white band with brown feathers with dark edge-lining below it. The front is light-grey, with finely barred grey flanks and rump. The wings are dark-grey, with white tertiaries and white inner patches. Females have a brown head, with a darker grey-brown stringy crest. Lores and chin are light-grey. The front is light-grey, while the back is mottled grey-brown with grey edges. The flight feathers are dark-grey; only the tertiaries are white. Non-breeding males closely resemble females. The irises of both sexes are orange-red to bright-red. Both sexes have a long, narrow, slightly hooked, orange-red bill with a grey top side of the upper mandible and the name-giving sawtooth edges. The legs and feet are orange-red. Juvenile Red-breasted Mergansers resemble females, but with a duller red bill and a less conspicuous crest.

The overall distribution of this species can be assessed, and specific locations where birds have been spotted can be found, based on individual sighting reports submitted by birdwatchers to ebird.org .

The global distribution of the Red-breasted Merganser is available HERE .

Red-breasted Mergansers are a migratory species that populates parts of the northern hemisphere, all around the globe at medium to high geographic latitudes. In North America they can be found permanently along the coastlines of British Columbia and southern Alaska. In addition to Iceland, they are permanently present in Ireland, NW England and Scotland, in Denmark and along the southern Norwegian North Sea coast. During the breeding season they extend their range to encompass basically the entire mid- to high-latitude northern hemisphere, all through Canada (except the south-western inland across the Rocky Mountains), the north-western US (Great Lakes to Newfoundland) and some parts of the south-eastern coastline of Greenland. They also extend their range into almost all of Scandinavia and on into northern Asia, out to the Bering Sea in the East. The far eastern migrants spend the northern winters in Japan, western Korea and the Chinese coastline. Eurasian migrants winter over along the western Caspian Sea, the central northern coast of Turkey and all the way from the western Black Sea via Greece and the Bosporus through the eastern Adriatic coastline to about Trieste. There are populations in southern Germany, in the Mediterranean coast in the border region of France and Spain, in northern Portugal and along the Atlantic/North Sea coastline from the Pyrenees to the German/Danish border, as well as south-east England. In North America the winter grounds span both the Atlantic coastline (from Newfoundland to the US/Mexican border) and the Pacific coastline(from British Columbia to the US/Mecian border).

In Europe, apart from wintering grounds in the border region of southern Germany, Austria and Switzerland, Red-breasted Mergansers are found primarily in (near-)coastal areas; for details see Wikipedia.

The first time we spotted Red-breasted Mergansers was at the Amsterdamse Waterleidingduinen, near Amsterdam, Netherlands, in 1998.

J. Pires reports spotting Red-breasted Mergansers in the Sado estuary, Setubal, Portugal, in January 2023. More were found at the same location in February 2025.

In September 2024, C. Pears found a large mob of Red-breasted Mergansers together with a small number of Goosanders in Tromso, Norway.