Crepuscular is a term used to describe some animals that are primarily active during twilight, that is at dawn and at dusk. The word is derived from the Latin word crepusculum, meaning "twilight." Crepuscular is thus in contrast with diurnal and nocturnal behavior. Crepuscular animals may also be active on a bright moonlit night. Many animals that are casually described as nocturnal are in fact crepuscular. Within the definition of crepuscular are the terms matutinal (or "matinal") and vespertine, denoting species active only in the dawn (matutinal) or only in the dusk (vespertine), respectively.
The patterns of activity are thought to be an antipredator adaptation. Many predators forage most intensely at night, while others are active at mid-day and see best in full sun. Thus the crepuscular habit may reduce predation. Additionally, in hot areas, it may be a way of avoiding thermal stress while capitalizing on available light.
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