Two Gulls, One Confusing Pair

Stand on almost any British seafront and you will meet two large gulls within a few minutes of each other. The herring gull is the classic seaside bird — the one that steals your chips and sounds like a laugh track. The lesser black-backed gull is its darker, sleeker cousin, often standing a few metres away on the same railings, looking almost identical at a glance. They nest on the same rooftops, squabble over the same discarded pasties and follow the same ploughs inland. Yet they are different species, with different habits and different fortunes, and once you know what to look at they become surprisingly easy to tell apart.

Leg Colour: The Quickest Clue

Adults are straightforward. An adult herring gull has pink legs and feet — a soft, fleshy pink, never yellow. An adult lesser black-backed gull has bright yellow legs, sometimes edging towards orange-yellow in high summer. On a bird standing on a wall or paddling in the shallows, this single feature settles the identification in most cases.

The caveats matter, though. Young birds of both species start life with pinkish-flesh legs, and a lesser black-backed gull's legs only colour up properly as it matures through its second and third years. There is also the yellow-legged gull, a scarce visitor to southern Britain, which has yellow legs and a back as pale as a herring gull's. So never rely on legs alone — check the back as well.

Back Colour and Wing Pattern

Look at the mantle, the grey area across the upper back and shoulders, in good light and preferably alongside the other species for comparison.

• Herring gull: a pale, silvery-grey back, light enough to look almost white in bright sunshine.
• Lesser black-backed gull: a distinctly darker slate-grey back, several shades deeper, closer to charcoal than silver.
• Wingtips: both have black wingtips with white spots known as mirrors. On the lesser black-backed gull the black extends further up the folded wing, so the contrast with the dark back is far less striking than the crisp black-and-pale-grey pattern of a herring gull.
• Bill: both have a yellow bill with a red spot near the tip on the lower mandible. The lesser black-backed gull's bill is often slightly longer and more slender, and its eye is usually a brighter yellow.

Size, Shape and Flight

Size alone is unreliable: a large lesser black-backed gull can easily outweigh a small herring gull. Shape is a better guide. The lesser black-backed gull is slimmer and more elegant, with a smaller, rounder head, longer wings and longer legs, giving it a slightly leggy, almost tern-like look. The herring gull is bulkier and chestier, with a bigger head and a hunched, shoulder-heavy stance.

In flight, the lesser black-backed gull's longer, narrower wings and slower, more elastic wingbeats make it look purposeful and unhurried, often patrolling steadily offshore. The herring gull's flight is more lumbering and gull-like, with looser, flappier action and plenty of gliding and hanging on the wind.

Sorting Out Young Birds

Immature gulls are brown, mottled and genuinely difficult. Juvenile lesser black-backed gulls are usually darker and more chocolate-brown, with a dark head, strongly patterned pale-fringed feathers on the back, and a noticeably barred rump and tail. Young herring gulls are paler, greyer-brown and sandier, with a paler head and less contrast overall.

By their first spring, young lesser black-backed gulls start to show yellow in the legs, which helps. Even so, moulting, worn and intermediate birds occur, and the two species occasionally hybridise, producing offspring with mixed features. If a bird looks wrong, it is perfectly acceptable to leave it unidentified.

Voice, Season and Habits

Sound is a useful backup. The herring gull's long call is the famous laughing yelp, a rising series of notes often written as kya-kya-kya. The lesser black-backed gull's equivalent is deeper, more nasal and drawn out, a wailing, almost complaining note that carries well over a harbour.

Their calendars differ too. The herring gull is with us all year, inland and on the coast, and is a familiar rooftop nester in towns. The lesser black-backed gull is largely a summer visitor: most British breeders leave in autumn for Iberia and North Africa, so winter birds are fewer and concentrated in the south and west. The lesser black-backed gull also feeds more at sea, taking fish, following boats and gathering on pasture and landfill sites, while the herring gull is the true opportunist of the promenade, the harbour wall and the picnic table.

Both are worth watching closely. The herring gull is red-listed in the UK because of long-term declines, while the lesser black-backed gull is amber-listed. Learning to separate them means your casual coastal count suddenly becomes useful information — and you will never again look at a yellow-legged, slate-backed gull on a Cornish harbour wall and simply call it "a seagull".