Great Black-backed Gull

How to find it

Treat this gull as a lucky surprise, not a target. The only documented place is Tortuguero, on the Caribbean coast, so that is where to scan the gulls along the shore. Look first for a size that dwarfs the birds around it. Then check the legs and back: pink legs and a blackish back point to this species. An adult black-backed gull here needs careful checking against the other accidental black-backed gulls on the national list. A clear photograph helps, because a record of an accidental species is only useful if the identification can be checked.

How to recognise it

Size comes first. This is the largest gull in the world, huge and heavy-billed, about 64 to 79 cm long with a wingspan of roughly 1.5 to 1.7 m. These marks describe the species in general, not only Costa Rican birds.

Adults show:

A white head and underparts.

A blackish-grey back and wings.

Pink legs.

A yellow bill with a red spot near the tip.

Young birds look very different. They are checkered brown and white above, black on the back appears gradually, and they take about four years to reach adult plumage.

What it sounds like

Recording: Yves Bas, CC BY 4.0, source, read 4 Nov 2026.

Behaviour and diet

This gull eats almost anything: fish, seabird chicks and eggs, small mammals, insects, carrion and rubbish. It scavenges on shores and at dumps, and it also hunts.

It is very aggressive and pirates food from other birds. A third-year bird has been seen driving an adult female goshawk off its kill. These habits describe the species across its range, not the Costa Rican bird.

Where it lives

Across its range it uses sandy or rocky coasts, estuaries and open sea, and in places it also visits large inland waters and fields. It breeds on the North Atlantic coasts and islands of northern Europe and northeastern North America.

In Costa Rica the only documented record comes from the Caribbean side, at Tortuguero in Limón Province. Avibase, whose checklist also covers Cocos Island, classes it as rare or accidental.

When to see it

The Costa Rican record dates from January 2018, so mid-winter is the only timing any source gives. No regular season is known.

Similar birds

Away from the west coast of North America, an adult with a black back and pink legs is very likely this species. Lesser Black-backed Gull is smaller and has yellow legs. The official Costa Rican list also gives accidental status to Lesser Black-backed Gull and California Gull, and Costa Rica has recorded ten gull species, mostly as sporadic vagrants, so a big dark-backed gull should also be checked against rarities such as Kelp Gull.

Names and lore in Costa Rica

Costa Ricans list it as Gavión atlántico, and also simply as 'gaviota', which is the general word for gulls.

Status and conservation

The official Costa Rican list classes the Gavión Atlántico as A, accidental, and the 2025-2026 list (June 2026 update) still does so, while its global status is Least Concern.

Photography tips

Scan the Tortuguero shore and canal mouth for a gull that dwarfs its neighbours. Get the legs, back colour and bill pattern in frame, since those are the marks that separate it from other black-backed gulls.