Like other species of howler monkeys, almost all mantled howlers have full three color vision. This is different from other types of New World monkeys, in which most individuals have two color vision. The three color vision exhibited by the mantled howler is believed to be related to its dietary preferences, allowing it to distinguish young leaves, which tend to be more reddish, from more mature leaves. Locomotion The mantled howler is diurnal and arboreal. Movement within the rainforest canopy and floor includes quadrupedalism (walking and running on supports), bridging (crossing gaps by stretching), and climbing. It will also sometimes leap to get to another limb. However, the mantled howler is a relatively inactive monkey. It sleeps or rests the entire night and about three quarters of the day. Most of the active period is spent feeding, with only about 4% of the day spent on social interaction. This lethargy is an adaptation to its low energy diet. It uses its prehensile tail to grasp a branch when sleeping, resting or when feeding. It can support its entire body weight with the tail, but more often holds on by the tail and both feet. A study has shown that the mantled howler reuses travel routes to known feeding and resting sites, and appears to remember and use particular landmarks to help pick direct routes to its destination. Communication The mantled howler gets the name "howler" from the calls made by the males, particularly at dawn and dusk, but also in response to disturbances. These calls are very loud and can be heard from several kilometers. The calls consist of grunts and repeated roars that can last for four to five seconds each. The volume is produced by the hyoid bone — a hollow bone near the vocal cords — amplifying the sound made by the vocal cords. Male mantled howlers have hyoid bones that are 25 times larger than similarly sized spider monkeys, and this allows the bone to act like the body of a drum in amplifying the calls. Females also call but their calls are higher in pitch and not as loud as the males'. The ability to produce these loud roars is likely an energy saving device, consistent with the mantled howler's low energy diet. The roars allow the monkey to locate each other without moving around or risking physical confrontations. The mantled howler uses a wide