© Copyright: Images: Jari Peltomäki, Jouko Lehmuskallio, Jari Hiltunen, M. & W. von Wright (Kansalliskirjasto, The National Library of Finland). Recording: Jan-Erik Bruun. All rights reserved.
- Family: Waterfowl – Anatidae
- Appearance: Medium-sized, slender ducks. Males have colourful plumage, females are drabber. Both sexes have a crest. Females and juveniles can be distinguished from the similar Goosander by the absence of a distinctive boundary on their necks between the colouring in their heads and chests. Bill slender all the way to the base.
- Size: Length 52–58 cm, wingspan 69–82 cm, weight 0.8–1.1 kg.
- Nest: Well concealed beneath a juniper shrub, in grassy vegetation or in a hole. Adds down to nest only during incubation.
- Breeding: 7–12 eggs laid in May–June(–July), incubated by female for 26–32 days. Ducklings leave the nest soon after hatching and learn to find food for themselves, though they stay together as a brood with their mother until they are fully grown. They learn to fly within about 2 months.
- Distribution: Breeds around nutrient-poor waters throughout Finland. Breeding population estimated at 25,000–35,000 pairs.
- Migration: By day or night. Leaves Finland June–November, returning April–May. Winters in Western Europe and around the Mediterranean. Some birds winter in the Åland Islands.
- Diet: Fish and invertebrates.
- Calls: Male almost silent. Females make a series of harsh calls.
- Endangerment: Near threatened, protected. Game bird in Finland. European red list status Near threatened, globally Least concern.
Red-breasted Mergansers are diving ducks. Males have more colourful plumage than the whiter male Goosander. They have a brush-like crest on the back of the head, and a white neck-ring between their greenish black head and reddish brown patterned breast. Females are more brownish and more evenly coloured than female Goosanders. The boundary between their pale brown heads and paler chests is not distinct. They also have crests, and white patches with a black central stripe on the trailing edge of each wing (cf. Goosander). They have red legs with darker webbed feet. Males have red beaks and irises. Females have reddish brown beaks and orange irises. Juveniles have brownish irises.