Bolivian Squirrel Monkey

Movements, Home range and Social organization. Group sizes of Black-capped Squirrel Monkey at Manu National Park and Biosphere Reserve are 35 - 65 individuals, and home ranges are 250 - 500 ha. Home ranges of different groups overlap, and there is no evident territorial behavior. Groups have been seen feeding on fruits in a large fig tree one after the other or even at the same time in neighboring Brosimum trees. There is, however, competition for food within groups. Food-based disputes are 70 times more frequent in groups of Black-capped Squirrel Monkeys (although still not very frequent) than they are in egalitarian and peaceful groups of the Central American Squirrel Monkeys where such aggressive interactions occur 0 - 3 times / hour. Only twelve aggressive interactions (all disputes over animal prey) were recorded in more than 3000 observations of Central American Squirrel Monkeys. In ¢. 23 % of encounters (95 % disputing fruit in fruiting trees), Black-capped Squirrel Monkey females interacted in coalitions; female Central American Squirrel Monkeys do not form coalitions. Female Black-capped Squirrel Monkeys stay in their natal group and, as adults, establish dominance hierarchies and develop alliances in kin-based coalitions. Male-male aggression is also common, and males also form coalitions. Males play no particular role in group vigilance and do not defend group members from predators. They disperse from their natal groups at 4 - 5 years of age and form allmale groups before attempting to join a mixed-sex group. Male coalitions are known to transfer between groups every 2 - 3 years. Females are dominant to males and keep them on the periphery of the group except during the mating season. Black-capped Squirrel Monkeys regularly travel with Large-headed Capuchins (Sapajus macrocephalus). The capuchin monkeys are usually the leaders, and it is believed that they help squirrel monkeys locate large crops of fruits such as figs. In a two-month study at Cocha Cashu, a group of 40 - 50 Black-capped Squirrel Monkeys associated with capuchin groups for ¢. 63 % of their time, with distances of 50 m or less between groups. Capuchin groups are smaller (8 - 12 individuals) and have smaller home ranges (c. 80 ha), so squirrel monkeys with larger home ranges associate with up to five different capuchin groups. Association with any particular capuchin group generally lasts about five days, but sometimes they travel together for up to twelve days. When in association with capuchins, squirrel monkeys eat more fruit and nectar and spend less time foraging for animal prey. Capuchins are larger but are outnumbered by the squirrel monkeys. Squirrel monkeys benefit from being led to large fruit crops, which capuchin monkeys are unable to monopolize, but there is a cost. Capuchins are able to monopolize medium-sized and smaller crops, which they locate with the help of the squirrel monkeys. Capuchins travel higher in the forest using more vines and palms where they forage for insects. Foliage gleaning squirrel monkeys, on the other hand, travel and forage more through small and medium-sized trees where they are more likely to discover small to middle-sized fruit crops, which can then be taken over by capuchins. Competition means that both capuchins and squirrel monkeys eat faster when they are traveling together. Capuchins can also dominate insect infestations, such as caterpillar swarms, to the detriment of squirrel monkeys. On the plus side, squirrel monkeys occasionally benefit by gaining access to otherwise inaccessible mesocarp of discarded and dropped Scheelea palm fruits during and following feeding bouts by capuchins. The ornate hawk-eagle (Spizaetus ornatus) and the Ocelot (Leopardus pardalis) are confirmed predators of Black-capped Squirrel Monkeys, and the harpy eagle (Harpia harpyja) and the black-and-white hawk-eagle (Spizaetus melanoleucus) have also been seen to attack them. C. Peres compared densities in terra firma and seasonally flooded (varzea) forests along the Rio Jurua. At two varzea sites in the Brazilian Amazon, he obtained densities of 70 - 7 ind / km? (Sacado do Condor) and 149 - 2 ind / km? ® (Boa Esperanca), and at six terra firma forest sites, also in the Brazilian Amazon, densities were considerably lower: 11 - 3 ind / km? * (Porongaba), 36 - 4 ind / km? (Kaxinawa reserve), 25 - 4 ind / km? * (Penedo), 28 - 7 ind / km? ® (Altamira), 7 - 7 ind / km? (Igarapé do Jaraqui), and 13 - 5 ind / km? * (Vai Quem Quer). Density in Manu National Park and Biosphere Reserve, Peru was 50 ind / km * in a forest of lacustrine succession (around Cocha Cashu).