For many animals, activity occurs during a particular temperature range. Crepuscular animals are active at dawn and dusk, the coolest times of day. The half-darkness makes prey animals less visible, yet visibility is good enough to locate food. Activity can change with the season, too. Snakes and lizards are diurnal (active during the day) in late spring and early fall, but they become crepuscular during the heat of summer.
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