Ethogram and Natural History of Golden-backed Uakaris (Cacajao melanocephalus)

Male-male affiliation and cooperation characterize the social behavior of the large-bodied pitheciids, Chiropotes and Cacajao: A review

Cooperation and affiliation between males may be key to the evolution of large multimale-multifemale primate groups in some species. Cacajao and Chiropotes form multimale-multifemale groups larger than those of most other platyrrhines (Cacajao: over 150 and Chiropotes: up to 80 individuals), and groups exhibit a high degree of fission-fusion dynamics. In both genera, males engage in affiliative, sex-specific behaviors and form all-male parties. Males in both genera also have conspicuous genitalia but can demonstrate sexual crypsis, or mimicry, wherein testes are retracted, resembling labia. Observed egalitarian interactions among males suggest that there is scramble competition for access to females, and aggression between males is uncommon relative to other social primates. As of yet, there are no genetic data to clarify dispersal patterns, and while relatedness among males would in part explain their affiliative relationships, there is some limited evidence for dispersal by males in Cacajao. In this review of recent studies of male-male social interactions in Chiropotes and Cacajao, we posit that the ability to maintain large groups in these genera may be related to the affiliative and perhaps coalitionary relationships between males, who may or may not be related. Affiliative male-male relationships may allow for monopolization of groups of females and facilitate group cohesion by reducing intragroup aggression; however data on male-male interactions with identified individuals will be required to determine patterns of affiliation, while genetic studies may be the most practical way of determining dispersal patterns for these genera.

Terrestrial activity in pitheciins (Cacajao, Chiropotes, and Pithecia)

Neotropical monkeys of the genera Cacajao, Chiropotes, and Pithecia (Pitheciidae) are considered to be highly arboreal, spending most of their time feeding and traveling in the upper canopy. Until now, the use of terrestrial substrates has not been analyzed in detail in this group. Here, we review the frequency of terrestrial use among pitheciin taxa to determine the ecological and social conditions that might lead to such behavior. We collated published and unpublished data from 14 taxa in the three genera. Data were gleaned from 53 published studies (including five on multiple pitheciin genera) and personal communications of unpublished data distributed across 31 localities. Terrestrial activity was reported in 61% of Pithecia field studies (11 of 18), in 34% of Chiropotes studies (10 of 29), and 36% of Cacajao studies (4 of 11). Within Pithecia, terrestrial behavior was more frequently reported in smaller species (e.g. P. pithecia) that are vertical clingers and leapers and make extensive use of the understory than in in the larger bodied canopy dwellers of the western Amazon (e.g. P. irrorata). Terrestrial behavior in Pithecia also occurred more frequently and lasted longer than in Cacajao or Chiropotes. An apparent association was found between flooded habitats and terrestrial activity and there is evidence of the development of a "local pattern" of terrestrial use in some populations. Seasonal fruit availability also may stimulate terrestrial behavior. Individuals also descended to the ground when visiting mineral licks, escaping predators, and responding to accidents such as a dropped infant. Overall, the results of this review emphasize that terrestrial use is rare among the pitheciins in general and is usually associated with the exploitation of specific resources or habitat types.

Multilevel Societies in New World Primates? Flexibility May Characterize the Organization of Peruvian Red Uakaris (Cacajao calvus ucayalii)

Researchers have described multilevel societies with one-male, multifemale units (OMUs) forming within a larger group in several catarrhine species, but not in platyrhines. OMUs in multilevel societies are associated with extremely large group sizes, often with >100 individuals, and the only platyrhine genus that forms groups of this size is Cacajao. We review available evidence for multilevel organization and the formation of OMUs in groups of Cacajao, and test predictions for the frequency distribution patterns of male–male and male–female interindividual distances within groups of red-faced uakaris (Cacajao calvus ucayalii), comparing year-round data with those collected at the peak of the breeding season, when group cohesion may be more pronounced. Groups of Cacajao fission and fuse, forming subgroup sizes at frequencies consistent with an OMU organization. In Cacajao calvus ucayalii and Cacajao calvus calvus, bachelor groups are also observed, a characteristic of several catarrhine species that form OMUs. However, researchers have observed both multimale–multifemale groups and groups with a single male and multiple females in Cacajao calvus. The frequency distributions of interindividual distances for male–male and male–female dyads are consistent with an OMU-based organization, but alternative interpretations of these data are possible. The distribution of interindividual distances collected during the peak breeding season differed from those collected year-round, indicating seasonal changes in the spatial organization of Cacajao calvus ucayalii. We suggest a high degree of flexibility may characterize the social organization of Cacajao calvus ucayalii, which may form OMUs under certain conditions. Further studies with identifiable individuals, thus far not possible in Cacajao, are required to confirm the social organization.