Best time to see: mid Oct to mid Apr

Key facts

Marine equivalent of the tufted duck, and superficially similiar

Habitat: sea, estuaries, occasionally inland on lakes and reservoirs

Annual winter visitor to the UK and Essex, breeding in Iceland, N. Europe and Siberia

Recognition

Male: black breast and rear end, dark head glossed green, vermiculated back; 48 cm

Often forms large flocks on open water, diving from surface to feed

Eats aquatic vegetation and molluscs; flight strong and powerful