- Lifespan
- 10–15 years in the wild
- Size & Weight
- 42–50 cm, wingspan 65–80 cm; 600–1,000 g
- Habitat
- Freshwater lakes, reservoirs, and slow-moving rivers with clear water and abundant aquatic invertebrates; winters on coastal waters and sheltered inland sites.
- UK Distribution
- Rare breeder in northern Scotland and the Highlands; winters throughout the UK, particularly on larger freshwater bodies and estuaries, with numbers boosted by continental migrants from September to March.
- Diet
- Primarily aquatic invertebrates, especially freshwater amphipods, insect larvae, and molluscs; also small fish and occasional plant matter.
- Prey
- Freshwater amphipods, dragonfly nymphs, chironomid larvae, small fish, molluscs
- Predators
- White-tailed eagles, pike, cormorants, and occasionally foxes targeting nesting females
- Mating Season
- December to April, with courtship displays on wintering grounds
- Breeding
- Clutch of 8–10 eggs, incubation period 28–32 days, single brood per year; uses tree cavities or nest boxes; females are highly philopatric
- Behaviour
- Highly vocal diving duck producing distinctive whistling calls; males perform elaborate courtship displays including head-throwing and rapid swimming. Highly gregarious in winter, forming large rafts on suitable water bodies. Dives to considerable depths to forage on lake and river beds.