The forelimbs of bats are so highly modified for flight that they are of little value for terrestrial locomotion. Deprived of all but limited use of the front feet in terrestrial activity, roosts or resting sites are also limited. All bats are primarily nocturnal and most of them spend the day in elevated, secluded retreats. Elevation is critical, for some bats show limited ability to take flight from flat, horizontal surfaces. Many bats, however, do show marked agility on the ground, and are quite capable of gaining flight from flat, horizontal surfaces. There is little correlation between taxonomy and roosting habits, although utilization of vegetation as roosts appears to be the general rule in the Megachiroptera and rather uncommon in the Microchiroptera
