- Lifespan
- 15–20 years in the wild
- Size & Weight
- 50–71 cm, wingspan 80–108 cm; 1.0–2.3 kg
- Habitat
- Shallow coastal waters, estuaries, and rocky shores, with a preference for areas with kelp beds and mussel populations.
- UK Distribution
- Resident and migratory; breeds in Scotland and northeastern England, particularly the Farne Islands and Shetland. Winter populations are boosted by visitors from Scandinavia and Russia.
- Diet
- Benthic invertebrates, primarily mussels and other bivalves, along with crustaceans, sea urchins, and occasionally small fish.
- Prey
- Mussels (Mytilus edulis), cockles, clams, crustaceans, echinoderms
- Predators
- Great black-backed gulls, white-tailed eagles, mink, and occasionally grey seals; eggs and ducklings vulnerable to herring gulls and corvids
- Mating Season
- December to June, with peak activity February to April
- Breeding
- Clutch size 3–5 eggs; incubation period 26–30 days by female alone; single brood per year; ducklings fledge at 8–9 weeks
- Behaviour
- Highly gregarious outside breeding season, forming large rafts at sea. Males are highly vocal with distinctive cooing calls. Females are excellent divers and can reach depths of 30+ metres to forage.