The Yellow-tailed Woolly Monkey is a rare primate found only in the Peruvian Andes where they live in rough terrain in the cloud forest. They are arboreal and diurnal and adult males can reach sizes of 51.3 to 53.5 cm with tails even longer than the body and can weigh as much as 11 kg. Their fur is longer and denser than other woolly monkeys which is an adaptation to its cold mountain habitat. They are deep mahogany and copper with a whitish patch on their snout extending from the chin between their eyes. Their fur gets darker towards their upper body, making their head seem almost black. Their powerful prehensile tail is capable of supporting their entire body weight and it also uses its tail to help move through the canopy. They have been known to leap 15 metres. They live in large mixed social groups of approximately 23 individuals and they have a multiple-male group social system and a polygamous mating system. For all that, they have low reproductive rates and long inter-birth intervals, which adds to their vulnerability for extinction. They express aggressive behaviors upon initial encounters such as branch shaking, showing their buttocks, and making short barking calls. Their diet is primarily frugivorous, but they also eat leaves, flowers, insects and other invertebrates. Oddly, they also engage in geophagy, or the consumption of soil. Geophagy is a rare biological behavior but the species benefits from this tendency since it allows for the intake of minerals and the detoxification of the intestinal region of parasites and other diseases. Perhaps related to the fact that they tend to suffer from an iron deficient diet, their consumption of soil allows iron that they do not get from their regular diet. Although, like most primates, the Yellow-Tailed monkey has low birth rates, their main threats are all human-related. The last estimated population count was less than 250 individuals, largely because of the loss of habitat due to slash and burn agriculture. Afraid of losing their farmland to conservation efforts of the species, a rising population of farmers say they do not hunt the monkeys but that the land is necessary for growing coffee and raising cattle. The construction of new roads, habitat loss and fragmentation from agriculture, logging and cattle ranching, and subsistence hunting, together with the monkey's naturally low population densities, slow maturation, low reproductive rate, have led to a predicted decline of at least 80% over the next three generations. They are considered one of the world's 25 most endangered primates.