日本鳥類標識協会誌

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An individually marked population of Fan-tailed Warblers Cisticola juncidis was studied at Shinoda-yama grassland, Osaka, Japan between 1978 and 1982. An average male built 6.5 nests during one breeding season and three of them were accepted by females. The most successful male completed 18 nests, and mated with 11 females. About 50 to 70% males were polygynous over the four years. The extreme development of polygynous mating of the Fan-tailed Warbler results from the long breeding period due to plentiful food supply and the male having no role in parental care. While females were unfaithful to their first breeding sites and/or their mates. When nesting failure occurred, almost all the females deserted their mates and moved out of the territories. Even successful females frequently changed their mates. The low mate and site fidelity skewed the sex ratio towards females. Rapidly remating is not only a demographic predisposition favoring highly developed polygyny for males, but also an adaptive compensation for highly frequent, unpredictable nesting failure for females.

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