"Crepuscular" redirects here. For the atmospheric optical effect, see Crepuscularrays.For a definition of the term "crepuscular", see the Wiktionary entry crepuscular.
A number of factors affect the time of day an animal is active. Predators hunt when their prey is available, and prey try to avoid the times when their principal predators are at-large. The temperature may be too high at midday or too low at night. Some creatures may adjust their activities depending on local competition.