Most animals in the deer family are crepuscular, meaning that they are most active during dawn and dusk, rather than being strictly nocturnal creatures. Some deer alter their activity patterns to avoid hunting by humans, producing the phenomena of the "nocturnal buck" familiar to deer hunters.
Whitetail deer are the most common deer species east of the Rocky Mountains, and their behavior does not stray far from the rest of the deer family. Whitetails tend to be inactive during the day, resting in undergrowth and occasionally getting up to graze. Their main time of daylight activity is during the breeding season. During all other times, whitetail deer are most active at sunrise and sunset.
However, whitetail deer do respond to predation by changing their preferred time of day, so places that restrict deer hunting to daylight hours have many mature deer that are only active during the night to avoid being shot. Younger deer are less likely to change their activity in this way, due to inexperience.