GREAT NORTHERN DIVER Gavia immer

Great Northern Loon; Common Loon (N America)

L 69–91 cm, WS 127–147 cm.

 
IDENTIFICATION 

Large, bulky diver, exceeded in size only by some Yellow-billed. Compared with smaller species has stouter bill, heavier head, thicker neck and more steeply angled forehead (but note that largest Black-throated are as large as smallest Great Northern and former occasionally look thick-necked and can show fairly steeply angled forehead). Typically holds head and bill level (unlike Yellow-billed or Red-throated). Diving action smooth and powerful, lunging forwards to slide below surface. Adult summer distinguished from all but Yellow-billed by black head and neck (with green gloss), almost complete collar of black and white stripes on mid-neck (not easily seen at long range) and very extensive white markings on both upperparts and flanks. From Yellow-billed by black bill (note: can be whitish towards tip). 

Adult winter/Juvenile distinguished from all but Yellowbilled by head and hindneck darker than back, white eye-ring (on many), pale indentation into dark hindneck at middle of neck (white in adult, brownishwhite in juvenile) and broad dark half-collar at base of neck. From Yellow-billed by pale greyish-white bill with black culmen, black cutting edges to mandibles and often a black tip. (Note: bill sometimes looks all whitish-grey, especially in late winter, so superficially recalling winter Yellow-billed.) Always lacks distinctive bill shape of Yellow-billed (q.v.) and rarely holds bill angled upwards. Body outline is often subtly different: in Yellow-billed the highest point is usually above the mid-point while in Great Northern it is typically further forward, making body seem longer. Outline can vary, however. Beware young juvenile Great Northern or bleached adult winter with paler, browner head, hindneck and half-collar and, in case of former, obvious pale scaling on upperparts; such birds recall both Black-throated and Yellow-billed in some respects. Birds moulting into adult summer plumage have blackish appearing on head/neck and more extensive white markings on upperparts than Black-throated. 

In flight, wingbeats slower, heavier, more flexible and less stiff than Black-throated. Head, bill and neck noticeably bulkier, the neck quite well drooped but head held up. Feet very prominently projecting, making broader wings seem very centrally positioned. Dark flank line very obvious and (in all but adult summer and some juveniles) white ‘indentation’ and dark half-collar on neck often visible and more obvious than in Yellow-billed.

SEX/AGE 

Juvenile resembles adult winter, but has prominent pale fringes to feathers of upperparts and paler, browner crown/hindneck (most obvious until middle of first winter). Lower face browner and some dusky brown on throat and foreneck. Pale areas above and below eye less white and so less obvious. Looks a little less bulky, with bill a little slimmer.

VOICE 

On the breeding grounds gives a loud, repeated, haunting yodelling, ‘a-a-whoo-kwee-wheeooo- kweewheeooo’, also a tremulous scream resembling manic laughter, a long howl and a low moan.

STATUS/HABITAT 

Locally not uncommon. (In addition to mapped range, has bred Britain.) Like Blackthroated, generally breeds by larger lakes with deeper water. At other times frequents coastal waters; occasionally inland lakes.