Dominant-subordinate relationship among eight species was investigated at the individual level in mixed, winter flocks of birds in Hokkaido, Japan. In five pairs of species, some individuals of averagely smaller species always dominated those of averagely larger species on average, large species. The characteristics of individuals causing dominance reversal were examined for body size, sex and residency for each pair of individuals. Among individuals of Nuthatch Sitta eurpaea and Japanese Pygmy Woodpecker Dendrocopos kizuki, in which body size largely overlapped and both were residents, their dominance was perfectly related to body size. Between species for which body size did not overlap, i.e., Marsh Tit Parus palustris and Great Tit P. major, and Great-spotted Woodpecker D. major and two larger woodpecker species (White-backed Woodpecker D. leucotos and Grey headed Woodpecker Picus canus), resident males of small species often dominated immigrants of large species. This result can be due to site- or sex-related aggressiveness of individuals.

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