How to identify the Great Black-backed Gull

To correctly identify the Great Black-backed Gull (Larus marinus), check each of these features. Birds can be tricky: habit, habitat, and call often confirm a sighting that a single photo cannot.

Size at a glance

Length

64-79 cm (25-31 in)

Wingspan

150-170 cm (59-67 in)

Weight

1.3-2.3 kg (2.9-5.1 lb), with some individuals reaching up to 2.5 kg (5.5 lb)

Physical features to check

1. 1

   Plumage

   Overall feather coloration and pattern.

   Adults have a dark slate-grey to black mantle and back, contrasting sharply with pure white underparts. The head, neck, and tail are also white. The primary wing feathers are black with white tips. Juveniles are mottled brown and buff, gradually acquiring adult plumage over several years.

2. 2

   Beak shape

   Shape and color of the bill: a key field mark.

   Large, heavy, and yellowish-orange bill with a prominent red spot on the gonys (lower mandible). Juveniles have a dark bill that lightens with age.

3. 3

   Eye color

   Iris color and any distinctive eye markings.

   Pale yellow, surrounded by a reddish orbital ring.

4. 4

   Leg color

   Leg and foot color.

   Pinkish.

5. 5

   Distinguishing features

   Standout features that separate this species.

   Its immense size, very dark mantle, and powerful bill are key distinguishing features. The dark back is significantly darker than that of Herring Gulls or Lesser Black-backed Gulls.

6. 6

   Juvenile appearance

   How young birds differ from adults.

   First-year birds are mottled dark brown and grey-brown overall, with pale bases to the primaries forming a 'wing window' in flight. The bill is entirely dark. Over the next few years (second-winter, third-winter), plumage becomes progressively less mottled, with areas of white appearing, and the mantle starts to darken. Full adult plumage is typically attained in the fourth or fifth year.

7. 7

   Seasonal changes

   Plumage variation between breeding and non-breeding seasons.

   Adult breeding plumage is pristine white on the head and underparts with a dark mantle. In non-breeding plumage (winter), faint streaking may appear on the head and neck, but it is much less pronounced than in many other gull species.

8. 8

   Sexual dimorphism

   How males and females differ.

   Males are generally slightly larger and heavier than females, but plumage is identical.

Key field marks

• Size. It is the largest gull species, noticeably larger and bulkier than any other gull in its range. This alone is often the best initial identification clue.
• Mantle Color. The deep slate-grey to black color of its back and upperwings (the 'mantle') is distinctive and much darker than other large gulls, forming a strong contrast with its white head and underparts.
• Bill. A very large, powerful, yellowish bill with a prominent red spot on the lower mandible is characteristic.
• Leg Color. Adults have pinkish legs, which distinguish them from Lesser Black-backed Gulls (yellow legs).
• Juvenile Plumage. Juveniles are heavily mottled brown but possess a very powerful bill and a large overall size. Look for the pale 'wing window' at the base of the primaries in flight.
• Voice. Its deep, guttural calls and powerful 'laughing' vocalizations are lower pitched than those of smaller gulls.

Explore the Great Black-backed Gull