Medium-sized gull with a long, slender bill. Breeding adult has a clean white head and dark red bill, and frequently shows a strong rosy-pink flush to the underparts. Non-breeding adult similar, but may show slight smudge on the head. Immature has orange bill with small brown patches on the wings, most readily seen in flight. Compare with Black-headed Gull; note Slender-billed's longer bill, sloping forehead, and "snouty" profile. Breeds in colonies in inland and coastal wetlands, but restricted to coastal wetlands when not breeding. Away from main range, found singly or in pairs, at times in association with much commoner Black-headed Gull.