A methodical survey of biological clocks and calendars, beginning with plants and proceeding with examples of daily and seasonal activity in small sea and shore animals, insects, reptiles, mammals, birds, and humans. Riedman lists five basic rhythms: circadian (24-hour cycles), tidal (24.8 hours), lunar (28 days), circannual (""around the year""), and ultradian (short intervals such as our 90-minute sleep cycles). Thus, a two-page description of ghost crab behavior ends with the summarizing statement that ""a ghost crab follows three rhythms: feeding at low tide (tidal rhythm of 24.8 hours); resting in burrows on circadian rhythm (24-hour cycle); and breeding and hibernating on circannual or seasonal rhythm."" A description of emperor penguins' breeding and brooding behavior ends with a mere ""surely biological clocks are timing these events""--but elsewhere Riedman cites experiments with artificial light which demonstrate that it is the presence or duration of daylight, not temperature or elapsed time, that governs silkworm development, lizard and rat breeding, ground squirrel hibernation, fox molting and pelt growing, deer antler growing and shedding, and bird activity levels. She then explains the workings of the pineal gland, the ""master clock"" in the brain, and the simpler ceil-level responses in simpler animals that lack a pineal gland. On the practical level, knowledge of biological clocks has proved useful in insect control, medical drug administration, managing sleep disorders, and alleviating jet lag. But the Groundhog Day superstition is just that, says Riedman, and studies have failed to confirm the belief that a full moon heightens mental disturbance. Sound and serviceable.