Pallas's gull

Pallas's gull (Ichthyaetus ichthyaetus), also known as the great black-headed gull, is a large bird species. As is the case with many gulls, it has traditionally been placed in the genus Larus. The scientific name is from Ancient Greek. Ichthyaetus is from ikhthus, "fish", and aetos, "eagle".

This is a very large gull, being easily the world's largest black-headed gull and the third largest species of gull in the world, after the great black-backed gull and the glaucous gull. It measures 55–72 cm (22–28 in) in length with a 142 to 170 cm (56 to 67 in) wingspan. Weight can vary from 0.96–2.1 kg (2.1–4.6 lb), with an average of 1.6 kg (3.5 lb) in males and 1.22 kg (2.7 lb) in females. Among standard measurements, the wing chord is 43.5 to 52 cm (17.1 to 20.5 in), the bill is 4.7 to 7.3 cm (1.9 to 2.9 in) and the tarsus is 6.5 to 8.4 cm (2.6 to 3.3 in). Summer adults are unmistakable, since no other gull of this size has a black hood. The adults have grey wings and back, with conspicuous white "mirrors" at the wing tips. The legs are yellow and the bill is orangey-yellow with a red tip.

In all other plumages, a dark mask through the eye indicates the vestiges of the hood. The call is a deep aargh cry. Young birds attain largely grey upperparts quite rapidly, but they take four years to reach maturity.