Slender-billed Gull vs Audouin's Gull

In short

The bill shape and color are the most reliable field marks: the Slender-billed Gull has a long, thin, and slightly drooping bill, while Audouin's Gull features a shorter, thicker, and straighter bill. Audouin's Gull also has a distinctive red bill with a black band, unlike the plain bill of the Slender-billed Gull.

Identification tips

• Look for the bill shape and color: Slender-billed Gull has a long, thin bill; Audouin's Gull has a shorter, thicker red bill with a black band.
• Check the size: Audouin's Gull is larger and more robust.
• Observe the head pattern: Audouin's Gull may show a darker eye mask during the breeding season.

Size

Audouin's Gull is generally larger and more robust than the Slender-billed Gull.

Plumage

Both species have similar overall plumage tones, but Audouin's Gull has a more contrasting head pattern with a darker eye mask during the breeding season.

Habitat

Both species can be found in coastal habitats, but Audouin's Gull is more likely to be seen in rocky coastal areas and islands, while the Slender-billed Gull is often found in lagoons and estuaries.