The yellow-tailed woolly monkey (Lagothrix flavicauda) is a New World monkey endemic to Peru. It is a rare primate species found only in the Peruvian Andes, in the departments of Amazonas and San Martin, as well as bordering areas of La Libertad, Huánuco, and Loreto. Oreonax flavicauda is one of the rarest Neotropical primates and is one of Peru's largest endemic mammals. Adult head and body lengths can range from 51.3 to 53.5 cm, with tails even longer than the body, up to 63 cm (25 in). The average weight is 8 kg in adults, but some males reach 11.5 kg. Peruvian yellow-tailed woolly monkeys are similar in size to the common woolly monkey, also in the genus Lagothrix. They live in large social groups (around 23 individuals) of both male and females. They have low reproductive rates and long interbirth intervals, which adds to their vulnerability for extinction. They are known to express aggressive behaviors upon initial encounters such as branch shaking, "mooning" of the scrotal tuft, and short barking calls. The yellow-tailed woolly monkeys' fur is longer and denser than other woolly monkeys, an adaptation to its cold montane forest habitat. The monkey's color is deep mahogany and copper with a whitish patch on its snout extending from the chin to between its eyes. Its fur gets darker towards its upper body, making its head seem almost black. It has a powerful prehensile tail, with a hairless patch on its underside and a yellowish pelage on the last third of the tail, giving this species its name. This coloration of the tail is not seen in infants and juveniles. The powerful tail is capable of supporting the animal's entire body weight while feeding or just hanging around; it also uses its tail to help travel through the canopy. The monkey is also known for its long, yellowish, pubic hair tuft. It has the ability to leap 15 m (49 ft). The yellow-tailed woolly monkey is one of the least known of the primate species. It is also one of the largest neotropical primates. They are regularly found in the tropical Andes. Their habitat is characterized as rough terrain consisting of steep mountain sides and deep river gorges, with canopy heights of 20-25 m. Cloud forest, the habitat of this monkey, are in high altitudes and often have cloud coverage near or in them. The last estimated population count was less than 250 individuals. The current habitat of the yellow-tailed monkey is fragmented due to deforestation, as is the population.