Circadian and Circannian Rhythms
Certain mammalian behaviors serve to promote the survival of the individual. One striking aspect of animal behavior is the rhythmic, or cyclic, pattern of activity. Some species are active at night(nocturnal) and some during the day(diurnal); others are active primarily at dawn and dusk. The activity periods tend to be at regular intervals. The time of emergence of a particular species of bat may differ by no more than two or three minutes night after night. Animals also exhibit other kinds of cyclic behavior. The timing of reproduction is cyclic, and in some mammals, such as some rodents and bats, daily or seasonal shifts occur between highly active and torpid states. Migratory movements are also cyclic. Daily activity rhythms, those based on a 24-hour cycle, are termed circadian rhythms and are better understood than other types of rhythms.
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