Great Northern Bird is a large, with a striking breeding plumage of a glossy black head and neck that ends with a sharp line against a white breast and underparts, a ring around the lower neck of vertical white marks, plus a smaller white chinstrap. The sides of the breast of Great Northern Bird are lined with tight parallel black lines. The upperparts are black with a large area of white on the scapulars and mantle forming a loud chequerboard pattern. In summer the bill is blackish, turning a silver-grey in winter with a dark culmen, and is held level while swimming. In all plumages the 'boxy' shape of the head is distinctive with a steep forehead and flat crown. The winter and juvenile plumages are essentially dark above and pale below, whitish from bill to breast, with a dark half-collar on the lower neck.
Great Northern Bird is essentially a Nearctic breeder, in our region only nesting regularly in Iceland. Great Northern Bird requires large undisturbed lakes with reasonably deep water, small islands and islets for safe nesting, and plenty of space for a long take-off run. In winter it is found mainly on the north-western Atlantic coasts, favouring rocky shores and also often in sheltered bays, harbours and estuaries. In winter it occurs occasionally on inland water bodies such as reservoirs.
A wide variety of calls of Great Northern Bird is given in the breeding area, the most famous being an evocative laughing tremolo, commencing with a lower pitched note, very difficult to transcribe but which goes something like "aah-hooo-hoo-hoo-hoo-aah" or "uhh'hw'hwa'hw 'hw'hw'hwa'ho". It also gives a loud rising wail "arrr-ooo-rr-ooooh", and a more strident chorus of clearer syllables "aow-arr'ow'arr'ow'arr' wow-wah, wow'wah, wow'wah..." or "a-a-woo-kuee-kuee-wheeoo-kwee-wheeoo". All these calls serve a territorial or display function on the breeding grounds. In autumn flocks may give a conversational single-syllable moaning call.