Pitheciid social organization is quite variable. Callicebus is unique among pitheciids in exhibiting a pair-bonded, monogamous social structure, living in groups of 2-6 individuals (adult couple and offspring). Pithecia species live in small multimale/multifemale groups. Chiropotes lives in

A brown titi (Callicebus brunneus) near upper Madre de Dios River in South America. (Photo by © Kevin Schafer/Corbis. Reproduced by permission.)
A southern bearded saki (Chiropotes satanas satanas). (Photo by Claus Meyer/Minden Pictures. Reproduced by permission.)

multimale/multifemale groups of 10-30 individuals with a roughly equal sex ratio, while Cacajao lives in large multimale/multifemale groups of up to 100 individuals.

Grooming behavior is important in reinforcing social bonds in Callicebus and may account for 10% of a day's activity. Group members also twine their tails when sitting together. When aggravated, Pithecia exhibits an aggressive display of piloerection, body shaking, an arched posture, and a growling vocalization. Chiropotes has a distinctive tail wagging behavior that denotes excitement, and a characteristic high-pitched whistling vocalization. Cacajao also exhibits tail wagging and piloerection, and the naked-faced Cacajao calvus has the largest repertoire of facial expressions of any platyrrhine.

Callicebus lives in small, well-defined territories that in most species are defended using loud vocalizations (solo male calls and male-female duets). In other species there is overlap of home ranges, and calls are used to define territories without boundary defense. They rarely associate with other primate species, but have been observed occasionally with tamarins (genus Saguinus) and marmosets (genus Callithix). Pithecia generally occupies small home ranges, but some species may have large ones. The home ranges of some species may overlap, while others may have relatively exclusive areas with defined boundaries and little overlap. They have not been observed to form polyspecific associations with other primates. Both Chiropotes and Cacajao have large home ranges that are not defended. Chiropotes has been observed in poly-specific groups with squirrel monkeys (genus Saimiri), capuchin monkeys (genus Cebus), and Cacajao; and Cacajao has been observed to associate with squirrel monkeys (genus Saimiri), capuchin monkeys (genus Cebus), woolly monkeys (genera Lagothrix, Pithecia, and Chiropotes).

Both Pithecia and Chiropotes have relatively shorter day ranges than do the other two pitheciid species. Pithecia has short day ranges, usually less than 0.6 mi (1.0 km). Most Pithe-cia species locomote by vertical clinging and leaping and tend to prefer the lower and middle strata of the forest canopy, although Pithecia albicans uses the middle and upper canopy and does little vertical clinging. Some species will forage occasionally on the ground. Day ranges are much longer in Chiropotes (0.6-2.8 mi [1.0-4.5 km]), and increase during periods of food scarcity. Groups may fission for feeding. Travel is cohesive but they may also travel in subgroups. Chiropotes is an arboreal quadruped that prefers the upper canopy, traveling rapidly between feeding trees and then engaging in intense feeding bouts. Cacajao also has very long day ranges (greater than 3 mi [5 km]), and prefers the middle and upper canopy, but will forage on the ground during the dry season due to the paucity of terrestrial mammals in flooded forests. They are arboreal quadrupeds, but employ more leaping and bipedal suspension postures than other pitheciids. All Callicebus species are primarily arboreal quadrupeds and rarely forage on the ground. Some species use the lower canopy, some the middle canopy, and some others the upper canopy.

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