Rabbits are NOT nocturnal they are crepuscular.
More Info: Actually, in the wild, rabbits are not nocturnal or diurnal but fall into a category known as crepuscular. Animals with a crepuscular circadian rhythm are most active at dawn and dusk rather than during the day or at night, and generally sleep both at night and during the day.
Rabbits Have a Retinal Clock
Current research suggests that the circadian rhythm of rabbits, like most other mammals, is influenced mainly by the amount of light hitting the retina. This is known as the retinal clock. In the absence of a rhythmic daily source of light, the rabbit’s behavior will no longer follow this pattern. The same thing will happen to a human’s circadian rhythm when deprived of a standard daily light cycle, such as when living near the North or South Pole.
Why is this Behavior Adaptive?
Because rabbits feed on foliage and usually have a continuous supply of food, their main concern is avoiding predators. Rabbits are prey to both diurnal predators such as hawks and nocturnal predators such as owls. Their crepuscular diurnal rhythm is most likely an adaptation that minimizes their exposure to diurnal and nocturnal predators by keeping them asleep in their warrens during these hours of the day and night.
Olek, Michael R.. “Species Profile: Cottontail Rabbit.” Messinger Woods Web Site – NYS Wildlife Hospital. N.p., n.d. Web. 1 Nov. 2012. http://www.messingerwoods.org/rabbitprofile.htm
Ribelayga, Christophe. “Identification of a Circadian Clock-Controlled Neural Pathway in the Rabbit Retina.” National Center for Biotechnology Information. N.p., n.d. Web. 1 Nov. 2012 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2883549/pdf/pone.0011020.pdf