Crepuscular is a term used to describe animals that are primarily active during the twilight. Crepuscular is thus in contrast with diurnal and nocturnal. 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 matinine and vespertine , denoting animals active in the morning (dawn) and evening (dusk) respectively.

Crepuscular mammals include the common mouse and rat. Crepuscular birds include Common Nighthawk and Spotted Crake. Some species have different habits in the absence of predators. For example, the Short-eared Owl is diurnal on those of the Galapagos islands that do not have buzzard species, but crepuscular on the others.