Piliocolobus oustaleti

Oustalet’s Red Colobus (scientific name: Piliocolobus oustaleti), also known as Oustalet’s Red Colobus, was once a subspecies of the Tana River Red Colobus and was classified as an independent species in 2013.

The Ustarai red colobus has a smaller family territory than other red colobus monkeys. The average family occupies nearly 9 hectares, while the corresponding average is 34-114 hectares. The average length is 603 meters. They live in the upper and middle layers of the forest and rarely come to the ground. Family groups consist of an average of 8-15 members, usually an adult male, several females, and their young. Several females will raise the young within the family group, and males will leave the family group before reaching adulthood, while females will remain in the family group.

Oustalé Red Colobus Like many primates, Oustalé Red Colobus often engage in social behaviors such as play, aggression, and intimidation. Play can be anything from chasing and wrestling to jumping off branches. Aggressive behaviors can be minor, such as grimacing, touching, or slapping. These are often associated with various body and limb gestures. Major aggression behaviors often include staring and glaring, often accompanied by slapping or shaking branches, and in extreme cases, physical violence. These aggressions often occur between males and are related to dominance and group status. In general, males attack each other more frequently than females, although the full effects of this behavior have not yet been examined for the small number of males in the Tana River red colobus species.

The Ustarai red colobus is a noisy, social animal that lives in heterosexual groups. Typically, red colobus live in groups of 30-50 members, including multiple males and females. However, in the reduced and fragmented habitat of the Tana River, the number of individuals in each group is much smaller, ranging from 12-30 individuals. In stark contrast to the rainforest species, Tana River red colobus groups are usually populated by only 1-2 males. These population statistics allow males greater access to mates and indirectly reduce pressure on the limited resources of their fragmented habitat. The causes and effects of the Tana River's small and fragmented habitat on red colobus behavior are still under investigation, but the differences between Tana River red colobus group size, low males, and rainforest species are quite clear.

The Oustalai Red Colobus is a herbivorous species, which is related to the morphological adaptations for this diet. All red colobus monkeys differ from other Old World primates in that they have a ruminant stomach rather than a simple stomach. This stomach consists of a large sac cavity, which is divided into four chambers like herbivores in order to digest crude fibers, and has a ruminating function. One of the proventriculus has an alkali/acid system designed to digest plant matter using bacterial fermentation. These primates also have high, pointed, ridged molars for shearing and folding leaves and seeds. This helps to break down cell walls and extract the nutrients contained therein. They mainly eat shoots, leaves and stems of plants, fruits of leguminous plants, but also fungi, wild fruits and cereals, including fruits and flowers. In a study on dietary choices, the Tana River Red Colobus ate not only young leaves (36%), but also fruits and seeds (25%, mostly immature), leaf buds (16.4%), mature leaves (11.5%), and flowers (6.2%). The top three plants consumed were the fig tree (29.4%), the plant garden Sorindeia obtusifoliolata of the Anacardiaceae family (19.6%), and Acacia (15.0%). These species contribute to the majority of the diet of the Tana River Red Colobus.

Males of the Ustare Red Colobus reach sexual maturity at about four and a half years of age, while females reach sexual maturity at about four years of age, after which females are known to have a prominent pink sexual swelling on their genitals during estrus. Mating and reproduction are possible all year round. The mating system in this species is usually polygamous, especially when there is only one male in the group. Usually, dominance determines who is allowed to mate, and in special cases, single males or males from other male groups often enter the family group to mate with females. During estrus, the female monkey's genitals swell, and this behavior is the female telling the male that she is ready to mate. The gestation period is 4.5-5.5 months, with an interval of 26 months. Weaning occurs before the baby is 20 months old, because continued suckling may inhibit the conception of another offspring.

When the Ustare Red Colobus is born, the skin on the back of the baby monkey is black and the lower abdomen is gray. The muzzle, ears and palms of the 3-4 week old baby monkeys are pink. The fur remains gray until 2-2.5 months old, starting from the head, and turns red on the crown. After birth, the baby monkey clings to the mother's abdomen and remains dependent on it. Generally speaking, the baby monkey always stays very close to the mother until 2-3.5 months old, at which time the distance is about 1 meter. At 3.5-5.5 months, they will play with other monkeys. At 18 months old, the young females of the group will move to another group and may continue to move from one group to another throughout their lives. The female membership in the group is very unstable. Some males may leave the group during adolescence, but are difficult to be accepted by another group in this patriarchal social structure.

The Ustare red colobus has a wide distribution range, from the Sangha River in western Africa to the east of the Obangui River to Lake Albert; the southern boundary of its distribution range is the Congo River, the eastern boundary is the Aruwimi River and the Ituri region, and in the north, its range extends to the savanna woodlands north of the Uele River. It is not close to the critical value of vulnerable and endangered species survival (distribution area or fluctuation range is less than 20,000 square kilometers, habitat quality, population size, distribution area fragmentation), and the population trend is stable, so it is evaluated as a species with no survival crisis.

Listed in the "Red List of Endangered Species of the World Conservation Union" (IUCN) 2016 ver 3.1-Least Concern (LC).

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Distributed in Congo, Central African Republic, Democratic Republic of Congo and South Sudan.
Inhabits subtropical and tropical dry forests and swamps.

The Oustale Red Colobus has a slender body, with a head-body length of 51-63 cm, a tail length of 52-75 cm, and a weight of 5-11.3 kg. The hair on the top of the head, back, outer side of the upper wrist, forehead, outer thigh, tail and other parts is gray to dark black; the pubic area is white; the hair on other parts is light orange to orange-red. This species has a brown-red crown on its head, and the cheeks, lips and nose are all black. Like other colobus species, the anal warts are very small and the tail is very long, which plays a role in balancing the body. The cheek pouches are also smaller than those of ordinary monkeys. They are different from leaf monkeys in that they have no thumbs, although the other fingers are particularly long, and the thumbs have degenerated into a small wart, so they are called colobus monkeys.
The Oustale Red Colobus has a prominent snout, strong jaws, 32 teeth, nostrils facing forward and downward, and 5 fingers and toes on both hands and feet,