This medium-sized gull features a long, slender bill. During the breeding season, adults have a clean white head and a dark red bill, often with a noticeable rosy-pink flush on the underparts. In non-breeding plumage, adults are similar but may have a slight smudge on the head. Immature birds have an orange bill with small brown patches on the wings, most visible in flight. To distinguish it from the Black-headed Gull, note that the Slender-billed Gull has a longer bill, a sloping forehead, and a “snouty” profile. It breeds in colonies in inland and coastal wetlands, but outside of the breeding season, it is found mainly in coastal wetlands. Outside its main range, it may be seen singly or in pairs, sometimes associating with the more common Black-headed Gull.