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Field Guide
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Red-breasted Merganser

Mergus serrator

Not yet photographed by the community

Spiky-crested sawbill of estuaries and sea lochs.

Species Profile

Amber List (breeding population); Green List (wintering population)
Lifespan
10–15 years in the wild
Size & Weight
52–58 cm, wingspan 70–86 cm; 900–1,300 g
Habitat
Found on coastal waters, estuaries, lochs, and larger inland lakes, preferring areas with good fish stocks and minimal disturbance.
UK Distribution
Breeds in small numbers in northern Scotland, particularly the Highlands and Hebrides. Winter visitors and passage migrants arrive from northern Europe, with larger populations occurring on British coasts from September to March.
Diet
Almost exclusively fish, diving to depths of 3–6 metres to pursue prey underwater with great agility.
Prey
Small fish including sand eels, sprats, herring, trout, and flatfish; occasionally crustaceans.
Predators
Foxes and mink raid nests; flying birds of prey such as White-tailed Eagles and Peregrines may take juveniles.
Mating Season
April to June
Breeding
Clutch of 8–10 eggs, incubation period 29–35 days, single brood per season. Ducklings fledge at 9–10 weeks.
Behaviour
Highly aquatic and rarely seen on land. Males perform elaborate courtship displays on water, producing distinctive grunting and rattling calls. Often seen in small flocks, diving synchronously to pursue fish.
Did You Know?
  • •Males have a distinctive dark green head with a shaggy crest and bright red bill, whilst females are grey with a reddish-brown head.
  • •They are among the fastest-diving ducks in British waters, using their legs positioned far back on their bodies for powerful underwater propulsion.
  • •Red-breasted Mergansers have serrated edges on their bills that act like a saw, helping them grip slippery fish.
  • •They have been subject to culling on some fisheries in Scotland due to concerns about predation on commercial fish stocks, though scientific evidence for significant impact remains debated.
  • •Unlike many ducks, mergansers rarely dabble at the surface; they are specialist pursuit divers that hunt entirely underwater.

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