The black-throated loon (Gavia arctica), otherwise known as the Arctic loon or black-throated diver, belongs to the loon (diver) family (Gaviidae). It is a large water fowl species, slightly larger than a domestic duck. Its body length averages 58—75 cm and the wingspan 110—140 cm.

Loons are found in Russia, northern Europe, and North America. They are so well adapted to water that have difficulty walking on the ground and are very seldom to be seen ashore. But they are excellent divers and can swim up to 300 m under water.

The males and females look alike: pure white breast and belly, dark upper parts. The back and upperwing of the black-throated loon have a contrasting pattern looking at a distance like big white splotches against a black background. During the mating period, the colouring changes as the neck and head grow ash-grey and the throat greenish or purple with metallic lustre.

The black-throated loon wings are narrow; in flight, it is fast but lacks manoeuvrability. When on water, it has a low sitting posture and, in case of danger, prefer to dive rather than take off. Loons can stay up to 2 minutes under water.

Typically, black-throated loons are found near deep, fish-rich lakes with sedge and rush shores. They avoid small lakes as they need a long water runway for take-off. A flying loon can move at about 60—65 km per hour. When the migration season comes, loons can fly even at night.

Loons’ couples are for life. Their nest is a heap of trampled down plant material with a slightly depressed tray. They usually arrange it on a gently sloping, grassy shore from which they can easily dive into water. The male and female sit on eggs in turn.