Great black-backed gull

The great black-backed gull (Larus marinus) is the largest member of the gull family, and it uses its size to advantage by bullying other seabirds into giving up their food. It is a common sight to see a bird such as a herring gull digging in the sand for a tasty morsel, only for a great black-backed (even a juvenile) to steal the catch and fly off with it.

The great black-backed gull is resident on the coasts of England, Wales and Scotland but in winter can be seen inland. It is also found in Scandinavia, Iceland, Greenland and on the east coast of northern North America.

Despite the great black-backed gull’s ability to survive alongside humans, the species has amber conservation status within the UK. Like all seabirds, it is at threat from oil spills and similar pollution threats.

Appearance

The great black-backed gull is around 75 centimetres (29 inches) in length with a wingspan of around 1.6 metres (5 feet plus). It is bulky in shape with a heavy head and stout bill, with broad wings and short legs. Adult great black-backs are mainly white apart from the back and wings (upper side). The upper wings also have white trailing edges. The bill is yellow with a conspicuous red spot on the lower bill. Males and females look alike.

Juveniles reach adult size within their first year but take four years to mature completely. Their plumage goes through various stages during this time, being mainly speckled brown.

Behaviour

In flight, the great black-backed gull is heavy and ponderous. It has a hunched attitude when perched. The call is deep and guttural.

As mentioned above, great black-backed gulls are piratical in their feeding habits, and are opportunists in that they will take food from whatever sources present themselves. These can include carrion and the eggs and young of other birds. They also eat fish, crustaceans, molluscs, and food waste left by humans.

Breeding

Great black-backed gulls are sometimes seen to nest as lone pairs but also in colonies, often in the company of lesser black-backed gulls. Both partners build the nest, which is usually on a cliff ledge but can be on the ground. Twigs, grass, seaweed and other materials are used, with feathers used as a lining. Two or three eggs are laid in May or June with both partners incubating them in turn, for up to 28 days.

The nestlings leave the nest soon after hatching, being fed by their parents for up to 50 days, by which time the flight feathers will have started to grow. However, young great black-backed gulls do not fly well until at least two months old. Only one brood is raised in a season.

© John Welford