The sun-tailed monkey was discovered in 1986 and this species of monkey is endemic to Gabon, West Africa. Their distribution area is estimated to be about 10,300 square kilometers. They are mainly centered in central Gabon. Their range is limited to the north and east because of three rivers. It is not really known to what extent the primate occurs in the west and south. Some studies show that the sun-tailed monkey can be found as far south as parts of the Lope National Park. They make their habitat in hilly, moist evergreen forests.
This species of monkey is classified as being vulnerable. The sun-tailed monkey has a very restricted range because they are at high risk from habitat loss and fragmentation. This species of monkey is semi-terrestrial, so it risks being trapped in ground snares as well. Since 1994 in Gabon, the government lists the monkey as a fully protected species. The monkey likes to live in areas with dense vegetation, like narrow valleys.
The sun-tailed monkey's diet consists of herbaceous plants, fruits, seeds, small vertebrate prey and insects. They are diurnal and go into the forest for a few activities. These monkeys can be seen from ground level up to two meters. They like to rest and groom at higher levels to avoid predators. The sun-tailed monkey sleeps in groups of about 17 individuals. The groups usually sleep 10 to 15 meters above the ground. Humans like to hunt this animal with snares and shotguns. When it is alarmed or threatened, it will flee to the ground.
The adult males defend their groups from other males. The female can give birth to only one offspring, when she reaches the age of four. More male monkeys are born than females. The male monkeys yawn to express tension. When they show signs of fear, they clench their teeth together. These monkeys have a cryptic nature and do not have high-pitched calls. They can be seen leaping from tree to tree with their bodies in vertical position. They also move by bipedal walking on the ground. They walk through grassy areas to avoid predators. Just a few of the sun-tailed monkeys are held in captivity in the country of Gabon. Many conservation measures are taking place to protect their habitat and range. Better protection of forests is needed in some areas where there is logging. Hunting of the sun-tailed monkeys is now being strictly controlled.