Black-throated Diver

Gavia arctica

58-73cm

Appearance

This is a sturdy water bird, larger than the Mallard. Its neck is thicker than the closely related Red-throated Diver, and it typically holds its bill (heavier and straighter than the Red-throated) horizontally. The sexes are similar, though the bird's plumage changes depending on the season. Its body is dark in summer with a grid of white patches on the back. It has a blue-grey nape and head, and its throat is black; it has a white 'chin strap' marking, the sides of its neck are white-striped and its underparts are also white. The winter adult is mostly grey-black on its upperparts and whitish beneath. During winter a white patch can often be seen in swimming birds along the flanks, the bird's dark cap lowers to eye level, and the bill pales. Juveniles are similar to the winter adult but the upperparts are browner.

Habitat

In Britain, breeding occurs exclusively in north-west Scotland where birds form nests beside big lochs. Outside breeding, it is mainly coastal, moving to sheltered bays and beaches, though it occasionally does visit inland habitats such as lakes and reservoirs.

Character

This bird dives often and swims low in the water. It has a habit of rolling on its side to groom the feathers on its belly. Forms small flocks outside of breeding season and groups gather to feed at fishing sites early in the morning. When flying, it looks black and white and heavier than the Red-throated; the head and neck are extended and the legs trail behind.

Food

Can dive up to 6m to pursue prey beneath the water. Diet is mainly fish such as Arctic charr, small brown trout, herring, sprats, sand eels, minnows and also insects and crustaceans.

Breeding

Pairs usually remain together for life. Female lays 2 eggs and incubates for 28-30 days with assistance from the male. Within 24 hours of hatching, the young leave the nest and are fed by the parents; they can fly after about 60 days.

Population

Approximately 200 pairs breed in Scotland; this number rises to around 550 individuals with an influx of birds from northern Europe in autumn and winter.

Observation Tips

Loch-side roads provide good vantage points with minimal disturbance. Check calm seas for swimming birds, or the sky for birds disrupted by onshore winds.

Voice

Predominately a silent bird, but has a loud wailing call when in breeding territory.
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