The Peruvian spider monkey (Ateles chamek), also known as the black-faced black spider monkey, is a species of spider monkey that lives in Peru, as well as in Brazil and in Bolivia. At long, they are relatively large among species of monkey, and their strong, prehensile tails can be up to long. Unlike many species of monkey, they have only a vestigial thumb, an adaptation which enables them to travel using brachiation. Peruvian spider monkeys live in groups of 20–30 individuals, but these groups are rarely all together simultaneously. The size and dynamics of the resulting subgroups vary with food availability and sociobehavioral activity. They prefer to eat fleshy fruit, but will change their diet in response to scarcity of ripe fruit. Individuals of this species also eat small animals, insects and leaves based on availability. Females separate from the band to give birth, typically in the fall. These females inhabit a group of core areas where resources are abundant in certain seasons. Typically, males exhibit ranging over longer distances than females, with movement of individuals enhancing the fluidity of subgroup size. Peruvian spider monkey are independent at about 10 months, with a lifespan of about 20 years. Characteristics The Peruvian spider monkey weighs up to . Its body can be long and the tail can be long. It has four elongated fingers and virtually no thumb, which is typical for spider monkeys but unusual for other monkeys. It can move easily through the trees and it has a prehensile tail like other species in the genus Ateles, which it uses to assist with brachiation. It has an agility that can only be compared to the gibbon of Asia. It has a life span of up to 20 years. Distribution The species occurs in central-northern of Bolivia, north-eastern Peru, and the central-western Brazilian Amazon. The species was recently found to occur in the northern bank of Solimões River, at the Mamirauá Reserve, where it probably colonized through a river meander cutoff process. They live primarily in lowland forests, occupying the canopy and the sub-canopy, but they have been observed using various habitat types, including dry and hilly areas such as the piedmont and cerrado forests, and have been observed to move depending on food availability. They were also observed living in Amazonian seasonally flooded forests. They live in territorial bands of 6–12 individuals whose territory covers about 20 square kilometers.