This is quite a large black bird with a pale greenish bill and wingspan up to 147cm (58ins). In strong sunlight the plumage appears dark brown. Most birds have a white patch beneath the bill, but this is not easy to see in flight. The legs and feet are black.

Flight is powerful with deliberate, slow wing beats and frequent long glides. They are silent at sea but make ear-piercing calls during courtship said to resemble a steel hammer tapping a small anvil, hence the old sailors’ names of ‘Shoemaker’ and ‘Cobbler’.

Birds return to their breeding colonies in late September. Burrows up to 2m (6ft) deep are excavated in soft tussac peat below dense tussac grass and the single egg is laid in late October or November on a small platform of peat or dry grass.

Young fledglings are covered in a soft grey down but by April they have grown their adult plumage and are abandoned by their parents. After losing weight for a few days, they leave the nest to fly out to sea on their own.