© Copyright: Images: Jari Peltomäki, Matti Leppänen, M., W. & F. von Wright: Svenska fåglar (Kansalliskirjasto, The National Library of Finland), Pohjolan linnut värikuvin. Recording: Jan-Erik Bruun. All rights reserved.
- Name also: Arctic Loon, Black-throated Loon
- Family: Divers – Gaviidae
- Appearance: Somewhat larger and thicker-necked than similar Red-throated Diver. Beak sturdy and dagger-like, with upper mandible slightly downcurved. Beak usually held horizontally (Red-throated Diver tilts beak upwards). Breast protrudes outwards by the waterline (unlike more “flat-chested” Red-throated Diver).
- Size: Length 63–75 cm, wingspan 100–127 cm, weight 2–3.2 kg.
- Nest: A low mound right by the waterline made of detached aquatic plants.
- Breeding: Almost invariably 2 eggs laid in mid May, incubated by both parents for 27–32 days. Fledglings learn to fly within about two months.
- Distribution: Breeds throughout Finland mainly by lakes with clear, nutrient-poor water. Breeding population estimated at 8,000–10,000 pairs.
- Migration: From August flies south towards wintering areas around the Black Sea and the Mediterranean Sea, returning from early April. Data from studies of the movements of ringed birds indicates that Black-throated Divers’ migration routes are shaped like a loop, with birds breeding in Siberia and Fennoscandia migrating in autumn over land to the Black Sea, but returning by a more westerly maritime route over the Gulf of Bothnia and the Gulf of Finland back to their breeding areas. Large migrating flocks made up of these large “Arctic” populations pass over Finnish marine waters in May.
- Diet: Fish typically found in clear-watered lakes (Perch, Bullhead, Roach), also some crustaceans and molluscs.
- Calls: Most frequent call a far-carrying and haunting “kwee-kow”.
Black-throated Divers are protected throughout Finland and the Åland Islands.
In their summer plumage Black-throated Divers have dark backs with rectangular white markings. They have dark grey colouring on the head and the back of neck, and black and white striping around their white chests and around a rectangular black throat patch. Their underparts are mainly white. Their legs are black on the outer side but pale grey on the inner side. In summer their beaks are dark and their irises are red.
Juveniles have brownish grey backs with scale-like patterning, but more greyish colouring on their caps and napes. A white thigh patch is often visible on young Black-throated Divers in the water. Their beaks are pale, and their irises are reddish brown.
In their winter plumage, Black-throated Divers have more uniformly dark upper parts. Their underparts are white, and a white thigh patch is often prominent. They also have white colouring on their throats and on their cheeks below their eyes. Their bills are pale grey and their legs are paler than in the summer, but their irises remain red.