The Red-breasted Merganser (Mergus serrator) is a slim, fish-eating duck with a shaggy double crest in both sexes — a bird of the archipelago and open coast, gathering along Swedish shores in winter. It breeds circumpolar across northern Eurasia and North America, nesting near water in forest and tundra habitats and wintering chiefly along sea coasts; its scientific name serrator means "sawyer", referring to the serrated bill that helps it grip slippery fish. It measures 52–58 cm with a wingspan of 67–82 cm and weighs 900–1,350 grams. The male has a green-black head with a shaggy, two-part crest, a white neck ring, a rust-brown, black-streaked breast, grey flanks, and a slender red bill; the female has a rust-brown head that blends gradually, without a sharp border, into the grey body, and a smaller crest — the shaggy crest present in both sexes is a good distinction from the Common Merganser.
The species is largely silent, though displaying males give faint, cat- or frog-like calls. Red-breasted Mergansers breed along the entire Swedish coast and at lakes in the mountain districts, with a national population estimated at 10,000–20,000 pairs; in winter, birds gather in groups along ice-free coasts and archipelagos, where the species is a short-distance migrant most easily seen. It nests on the ground, well concealed in dense vegetation, under a bush, in a rock crevice, or among stones, often near water on an archipelago island; the female lays around 8–10 eggs and incubates alone for just over four weeks, and the newly hatched young are taken quickly to the water, where they swim and dive from their first day — broods are sometimes combined, with several females' young forming a joint group watched over by multiple adults. Its diet consists mainly of small fish such as sticklebacks, sandeel, and young flatfish, caught by diving, with the narrow, serrated bill helping it hold onto slippery prey; crustaceans, worms, and aquatic insects are also taken, especially by young birds, and the species sometimes hunts cooperatively, driving fish shoals into shallower water.
Read about this species in Swedish →