Anecdotal reports of predation as well as observed predation attempts and rates of animal disappearance provide some of the most relevant data for evaluating the influence that predation risk may have on primate behavioural ecology. Here, we report rates of disappearance from six groups of red titi monkeys (Callicebus discolor) and two groups of equatorial sakis (Pithecia aequatorialis) followed over a period of four and a half years at a lowland site in Amazonian Ecuador. We also describe the first direct observation of a harpy eagle (Harpia harpyja) preying upon a titi monkey, as well as 3 unsuccessful attacks by tayras (Eira barbara) on titi monkeys and 4 unsuccessful attacks by various raptors on sakis. Our data indicate that pitheciid primates may face a wider array of possible predators than previously recognized, and that titi monkeys and sakis are susceptible to different major classes of predators. Our observations also suggest differences in the sex role during predator defence that could be related to the evolution and maintenance of monogamous systems.

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Fragmentation and habitat destruction are 2 factors driving the current decline of mammal populations. Spider monkeys Ateles spp. are some of the first neotropical mammals to go extinct after fragmentation, as they (1) are large-bodied, specialized frugivores that require large areas to subsist, (2) are preferred targets for local hunters, (3) have slow reproductive cycles, and (4) rarely move between adjacent forest fragments. Brown spider monkeys A. hybridus are Critically Endangered, and most of their historical habitat has either been cleared or is seriously fragmented. We conducted census surveys at 2 areas in Colombia (Las Quinchas and San Juan) in order to compare the population density of brown spider monkeys, red howler monkeys Alouatta seniculus, and whitefronted capuchins Cebus albifrons in both continuous forest and recently fragmented forest in each of these 2 areas. We found a higher density of brown spider monkeys and red howler monkeys in recent fragments at both sites, while differences were not consistent for white-fronted capuchins. We suggest that these patterns could be explained by the constrained ability of spider monkeys and howler monkeys to move between forest fragments and to exploit impacted or degraded areas. In the absence of hunting, the immediate effects of fragmentation on spider monkeys seem to lead to a sudden increase in population density as a result of a decreasing forested area, while maintaining population numbers relatively stable. Longer-term research will lead to the identification of the proximate factors leading to the generalized pattern of local extinction of spider monkey populations in small isolated fragments.

We describe a new method for estimating population density of vocally responsive animals, which is based on playback calls coupled with auditory point transect sampling. The method yielded, for red titi monkeys (Callicebus discolor), better estimates than traditional line transect surveys. We propose it as an effective alternative for sampling certain cryptic, but vocally responsive animal species.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.

Socially-monogamous primates are often described as displaying a suite of behavioral characteristics that includes a prolonged and essentially exclusive mating relationship between mates, joint participation of mates in territory defense, and extensive male involvement in offspring care. Amongst the pitheciins, titi monkeys (Callicebus spp.), and saki monkeys (Pithecia spp.) frequently live in sociallymonogamous groups. We present here comparative data collected over four years on the social interactions of Neotropical adult male and female titi monkeys (Callicebus discolor, n = 2 groups) and saki monkeys (Pithecia aequatorialis, n = 1 group comprising 2 different male-female pairs) in the Yasuní National Park and Biosphere Reserve in Ecuador. Our data suggest that these two pitheciins do not both fit the mold of "classic" social monogamy. Despite their similar grouping patterns, the two species differ markedly in the quality of the social relationships between pairmates. Saki pairmates are less affiliative and engage less in behaviors thought to be instrumental to the development and maintenance of pair bonds (e.g., grooming, coordinated vocal displays) than titi pairmates. There are also dramatic differences in the extent to which males invest directly in offspring. While titi males invest heavily in infants, saki males provide little direct paternal care. Male sakis may be providing indirect investment, but they certainly do not seem to mitigate the energetic costs of infant care for their partners to the same extent as titi males do. Thus, male sakis apparently remain in sociallymonogamous relationships for reasons disassociated from paternal care. Our results suggest that different ecological and/or social factors may underlie the expression of social monogamy in these two pitheciins.

A female spider monkey (Ateles belzebuth belzebuth) that gave birth to twins was studied during 13 months, and her activity budget and diet were compared to those of females with single offspring and females with no offspring to assess selective pressures that could influence litter size. We recorded qualitative information on the development and social interactions of the twins and three other single infants. Emi, the female that had the twins, had the highest proportion of resting time and the lowest proportion of feeding and moving time compared to other adult females and males. Emi also had the lowest average daily travel distance and relied more heavily on flowers and leaves than other group members who included a higher proportion of fruits in their diets. These results suggest that twins are energetically costly to spider monkeys because of the direct energy allocated into raising and carrying the twins and, also, because these costs have direct effects in the ability of a mother to obtain high-quality resources (e.g., fruits). The twins had a slower rate of physical and social development as well as a smaller body size compared to same-aged singletons by the end of the study. Thus, the extended periods of maternal care and the costs associated with rearing and carrying offspring are some of the factors that influence the evolution and maintenance of a litter size of one in most anthropoid primates.

Brown spider monkeys Ateles hybridus are one of the most threatened primates in the Neotropics. Most of the remaining populations of this species already live either in forest fragments or in areas that face imminent anthropogenic disturbance. Understanding how these animals cope with the challenge of living in small fragments, while at the same time being a large, frugivorous mammal is crucial to design effective conservation and management strategies. We studied the diet of wild A. hybridus and measured forest productivity in a small (~65 ha) fragment in the Magdalena Region of northern Colombia over a period of 26 mo. Spider monkeys at this site spent far less time feeding on fruits than reported in previous studies of Ateles spp. living in less fragmented sites. Moreover, we registered a high consumption of leaves in every month (on average 37% of their feeding time) as well as the consistent inclusion of decayed wood in the diet. Ficus trees can be considered staple feeding items, as they were present in high proportions in the monkeys' diet throughout the study. Although wild populations of spider monkeys can have flexible diets that include large proportions of leaves over long periods of time, they may also be exposed to a suboptimal diet which may have negative implications for their reproduction and well-being in the long run, further compromising the viability of wild populations living in disturbed habitats.

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