This is an immature. Smaller than similar Black-headed Gull, this species has an oddly shaped all black bill as seen here. This uncommon, poorly known species is listed as threatened by IUCN. It is a scarce winter visitor to Japan. In China, loss of Common Seepweed essential for breeding is the key threat. Some of this loss was caused by introduced Eastern Smooth Cordgrass which turns mudflat into salt-marsh while making seepweed grow too thick for nesting Saunder's Gulls.