The Black howler monkey exhibits a noticeably big neck and lower jaw with huge vocal cords. The largest New World monkey, this primate is also the largest monkey in rainforests of Latin America. This species has a well-defined sexual dimorphism with females, being smaller and displaying buff overall coloration. Additionally, newborn babies of this species also have buff fur. Another characteristic feature of these monkeys is their prehensile tails, acting as a 'fifth limb', allowing them to grip and hang from tree branches. Being arboreal animals, the Black howler monkeys spend majority of their time high in the trees, using their gripping tails quite often. Their diet mainly consists of various leaves, found aloft.
The natural range of this species covers central regions of South America, including eastern Bolivia, southern Brazil, Paraguay, and northern Argentina. Within this territory, the Black howler monkeys occur in a wide variety of habitats such as tropical semi-deciduous gallery forest as well as tropical deciduous forest with savanna-like areas. Due to their leaf-based diet, these primates prefer living in areas with diverse plant species, which they consume.
The Black howler monkeys are diurnal and social animals. They usually form units of 5 - 19 individuals, typically composed of 1 - 3 mature males and 2 - 4 mature females with their young. Males of this species are known to form bachelor herds. These animals are known to display territorial behavior, although each group will only defend the territory, where it resides. Home ranges of various groups tend to overlap. Every morning, community members emit howling signals, announcing of their location to neighboring groups. This behavior allows to keep distance between various groups. The Black howler monkeys also rub themselves on branches, thus marking their home range. Additionally, in the morning and evening, they mark their territories by defecating, occasionally leaving large dung piles.
Black howler monkeys are polygynandrous (promiscuous), which means that both males and females breed with multiple mates. Breeding occurs year round. Gestation period lasts for 180 - 194 days, yielding one infant, rarely - twins. The newborn baby is very small and weighs only 3.5 pounds (113 g). During the first month of its life, the infant will cling to the belly of its mother. After a while, it begins riding on her back. The mother will care for the baby, until it's about 1 year old. After reaching independence, females continue living with their natal group. The age of reproductive maturity is 5 years old in males and 3 - 4 years old in females.
The Black howler monkeys heavily suffer from hunting for their coat and meat. These animals are primarily threatened by loss and fragmentation of their natural habitat, as a result of cattle ranching as well as agricultural development for soy.
According to IUCN, Black howler monkeys are widely distributed across their range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC), although its numbers are decreasing.