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An infradian rhythm is a biological rhythm with a period longer than 24 hours. Due to the longer time frame for each cycle the frequency of occurrence in these cycles is lower than that of the circadian rhythms.
- female menstrual cycle
- bird migration
Like the ultradian cycle the infradian rhythms are not directly linked to circadian and diurnal rhythms and are not believed to be affected by the daytime/nighttime pattern or changes in the availablity of natural light.