Slender-billed Gull vs Black-headed Gull

In short

The bill shape is the most reliable field mark: the Slender-billed Gull has a long, thin bill, while the Black-headed Gull's bill is shorter and thicker. In flight, the Slender-billed Gull shows a more elongated appearance due to its longer neck and wings.

Identification tips

1. Bill shape: Look for the long, thin bill of the Slender-billed Gull compared to the shorter, thicker bill of the Black-headed Gull. 2. Head color in breeding season: Black-headed Gull has a dark brown head; Slender-billed remains mostly white. 3. In flight: Slender-billed Gull appears more elongated with longer neck and wings. 4. Habitat: Slender-billed is more coastal; Black-headed is more adaptable to various water bodies.

Size

Both species are similar in size, but the Slender-billed Gull appears more elongated due to its longer neck and wings.

Plumage

In breeding plumage, the Black-headed Gull has a distinct dark chocolate-brown head, while the Slender-billed Gull's head remains white with only a faint hint of grey. Outside the breeding season, both have white heads, but the Black-headed Gull often retains a dark ear spot.

Behaviour

Both species exhibit similar behaviors typical of gulls, such as foraging in flocks and scavenging, but the Slender-billed Gull may be seen more often in coastal areas.

Habitat

The Slender-billed Gull is more coastal, often found in saline lagoons and estuaries, while the Black-headed Gull is more adaptable, frequenting both coastal and inland water bodies.

Voice

The Black-headed Gull has a distinctive 'kree-ar' call, while the Slender-billed Gull's calls are less well-documented but generally softer and less raucous.