Mandrills will sleep in trees, in a different location each night. Drills rely on visual and vocal communication, while mandrills also use scent marking. They are one of the few Old World monkeys to have cutaneous glands. Alpha males scent mark the most frequently. Drills have a series of deep grunts used for close contact communication, to get their group together, and to begin movement.
Juveniles alarm bark more than the others.
Male mandrills have a 2-phase grunt or roar to round up their group. This expression can be interpreted as a threat by some inexperienced observers who note the display of the mandrills' large teeth. Despite their fierce appearance, mandrills can be quite pleasant personalities and have also demonstrated impressive cognitive abilities. Drills reach sexual maturity at about 42mos. Females have an estrus cycle of 35 days and gestation length of around 174 days.