Bearded saki socioecology: affiliative male–male interactions in large, free-ranging primate groups in Suriname

Bearded sakis (Chiropotes spp.) are among the least known primates in the world, particularly with regard to their social organization. However, extremely large and variable group size and growing evidence for affiliative relationships among males, make them a fascinating subject for studies of male–male tolerance and the evolution of large groups. During a 13-month study of free ranging Guianan bearded sakis (Chiropotes sagulatus) in continuous forest in Suriname, we documented variation in group size seasonally and social behaviour, particularly among males. We found that group size was smaller and more variable in the long dry season than the short wet season, perhaps in response to changes in resource availability. We found clear evidence of affiliative male–male relationships, with males being more social than females (89.2% of events involved one male versus 15.6% that involved one female) and typically socializing with other males (68.7% of events involved 2 or more males). We also found no evidence of hierarchical relationships between males (complete absence of agonistic interactions), and we documented unique male-affiliative behaviours and temporary all-male subgroups for the first time. To investigate potential explanations of male tolerance, we compared bearded saki social patterns to other multi-male group living primates (Ateline and Pan spp.). We found similarities with Brachyteles that suggest high intergroup mating competition and scramble competition for mates within groups.

Primate community of the tropical rain forests of Saracá-Taqüera National Forest, Pará, Brazil

Brazil is the richest country in the world in terms of primate species and the Amazonian rain forest is one of the richest biomes containing 15 (ca. 90%) of the Neotropical primate genera. Although considered key elements in conservation strategies, there is only anecdotal information on primates for several protected areas within the region. Here we present new data on the community composition of the primates in the Saracá-Taqüera National Forest (429,600 ha), an actively mined, bauxite rich area, in Pará, Brazil. We used information from the literature, technical reports, museum data, and interviews conducted with agents from the Brazilian Institute of the Environment and Natural Renewable Resources (Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis - IBAMA) and members of the local "Quilombo" community. In addition, from July 2003 to June 2007, we carried out 19 field trips ranging from 10 to15 days each, amounting to a total effort of 1,230 hours and 1,420 km of censuses, resulting in 1,034 records of eight primate species (Saguinus martinsi, Saguinus midas, Saimiri sciureus, Cebus apella, Pithecia pithecia, Chiropotes sagulatus, Ateles paniscus, and Alouatta macconelli). Two other species (Cebus olivaceus and Aotus trivirgatus) were recorded only indirectly, through interviews and literature data. In all, Alouatta macconelli was the most frequently recorded species (43% of all records); while Saguinus midas and P. pithecia were the least (ca. 0.4 and 0.6% of all records). Based on our results, we discuss group sizes as well as taxonomic problems concerning the genera Pithecia and Chiropotes, for which we registered individuals displaying phenotypic geographical variation and two different forms, respectively. Despite the deforestation inherent in bauxite mining, the Saracá-Taqüera National Forest still has a remarkable richness of primate species. Our study results place this National Forest amongst the richest reserves, in terms of primate species, in the Amazon region.