This paper describes the process of colonization of a small island (Furugelm Island) in Peter the Great Bay (Russian side of the Sea of Japan) by a gull species from the Larus argentatus superspecies complex, starting from a single nesting pair in 2004 to a stable population of 72 pairs in 2012. The taxonomic status of the colonist species remains debatable and is not the purpose of this paper. Rather, this is an analysis of the dynamics of regional colonization, characteristics of seasonal migration, and species biology that allow for the conclusion that these observations amount to a sequential colonization by Larus (smithsonianus) mongolicus of the eastern periphery of the Asian continent. The settlers colonized two habitat types from Lake Khanka to the lower reaches of the Amur River: large, freshwater lakes, and coastal islands. The birds that settled on Furugelm Island started as a group of seven differently-aged birds: two mature birds (that bred) and five younger birds of varying maturity. Successful colonization by this species was based on a series of factors, including the protected status of Furugelm Island where the birds fortuitously chose to nest, an abundance of available habitat and food resources, and a relatively low abundance of Slaty-backed gulls, which occupy the same niche.