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Seabirds are higher-order predators in the marine ecosystem and hence good indicators of the marine environment. Although the North Pacific has been the focal area for investigations of seabird faunal dynamics, the Pleistocene seabird fossil record has been scarce in the western North Pacific. Here, remains of 32 species of seabirds and related taxa (Anatidae, Podicipedidae, Gaviidae, Diomedeidae, Hydrobatidae, Procellariidae, Phalacrocoracidae, Scolopacidae, Laridae, and Alcidae) are reported from the middle–late Pleistocene Shiriya local fauna, northeastern Japan (Marine Isotope Stages 9 and 5e, ~ 320 and ~ 120 ka). This is the first substantial Pleistocene seabird fauna reported from the region so far, and includes globally first fossil records for Cepphus carbo and extant species of Aethia. The fauna also includes three extinct species, Shiriyanetta hasegawai, Mancalla? sp., and Uria onoi, the former two of which were flightless. The occurrence of immature individuals indicates that at least two species had nearby breeding sites. The seabird populations had probably been sustained by enhanced oceanic productivity in this area during their age, but oceanographic fluctuations in the subsequent glacial period, including the probable disappearance of a nearby oceanic front, would have seriously affected their subsistence, likely causing local extinctions of some species. [ABSTRACT FROM AUTHOR]