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Dietary preferences of white-faced capuchins monkeys (C. capucinus) in northwestern Costa Rica were examined across age classes and between two distinct seasons over the course of 1 year. The findings show that the dietary profiles of small juveniles, large juveniles, and adults are quite similar, suggesting that juveniles are efficient foragers from a young age. The predictions of several ontogenetic models are presented, and the data lend limited support to the juvenile risk aversion and motor ability models. [ABSTRACT FROM AUTHOR]

Adult-like locomotor behavioral patterns were found to develop at an earlier age in C. capucinus than in A. palliata. By 5 months of age, young Cebus resemble adults in the frequency of positional behaviors while young Alouatta individuals vary significantly from the adult condition. Young Alouatta (6–24 months of age) differed from adult Alouatta in leaping, bridging, and climbing. Leaping modes significantly decreased during ontogeny in Alouatta while bridging modes increased significantly during ontogeny. Cebus was observed leaping between gaps more often (juveniles and adults) than howlers, but did not exhibit significant changes in gap crossing behaviors beyond the infant stage of development. These data suggest that in a comparison of these New World monkeys, interspecific ontogenetic differences in linear growth, body mass, and life history timing did not predictably influence locomotion. [ABSTRACT FROM AUTHOR]

Studies on spatial cognition in primates and other animals indicate that landmarks serve as reference points, and may be encoded as distance and/or direction vectors in navigating to concealed or out-of-sight goals (dens, nests, feeding sites). In the present research, we conducted an experimental field study of spatial cognition and foraging strategies in a group of 15 wild white-faced capuchins (C. capucinus) in northeastern Costa Rica (10°26′N, 83°47′W). Specifically, we examined the ability of wild capuchins to use the geometric relationships of an array of two and three landmark cues to predict the location of baited feeding sites. The research design involved the construction of eight visually identical feeding platforms arranged in a circle with a diameter of 8 m. We then conducted a series of six experiments in which the relative spatial positions of experimentally manipulated landmarks (yellow- and pink-colored poles measuring 2 m in height) were the only information available to the forager to efficiently distinguish the location of reward and sham feeding sites. Our results indicate that over the course of 55 consecutive days and 227 experimental trials, the capuchins visited the feeding platforms 3262 times. Group members quickly learned to attend to the spatial positions of landmark arrays and use this information to compute the location of reward platforms. In addition, given that foragers arrived at the feeding station from different directions and encountered alternative views of the landmarks, it is possible that the capuchins were able to mentally rotate the configuration of the landmark array to efficiently solve this foraging problem. [ABSTRACT FROM AUTHOR]

A comparison of mantled howling monkey (A. palliata) body weights from the two Costa Rican populations at SR and LP plus the island population of BCI yielded average body weights of 6445 g for BCI females (N = 49), 5161 g for SR females (N = 21), and 4726 g for LP females (N = 663). Average male body weight for these same three populations was 7562 g for BCI (N = 38), 6573 g for SR (N = 15), and 5790 g for LP (N = 288). All three populations are sexually dimorphic with the males being significantly heavier than the females (BCI: F = 65.71, p < 0.00001); SR: F = 65.60, p < 0.00001; LP: F = 621.72, p < 0.00001). The BCI females are significantly heavier than the SR females (F = 80.48, p < 0.00001) and LP females (F = 360.50, p < 0.00001). The BCI males are significantly heavier than the SR males (F = 23.23, p < 0.00001) and the LP males (F = 295.50, p < 0.00001). The SR females are significantly heavier than the LP females (F = 10.25, p < 0.001) and the SR males are significantly heavier than the LP males (F = 26.54, p < 0.0001). Female weight at LP showed a seasonal difference while season had no effect on male weight. There were habitat effects on both female and male weights. Individual body weights at LP oscillated from 10% to 30% within and between years. These dramatic changes in body mass did not reduce life span nor affect infant survivorship. [ABSTRACT FROM AUTHOR]

Information on food selection and feeding habits is critical for species conservation, particularly in the context of forest landscapes heavily transformed by human activities. In this study, we examined the degree to which A. pigra feeding habits differed between two sites in the conserved forest of the Calakmul Biosphere Reserve (CBR) and two forest fragments outside the reserve, and how monkeys select the trees on which they feed. Our results suggest that howlers tended to exploit a smaller set of fruit and leaf species in the conserved sites, whereas their diet was more diverse in the fragments. This can be explained probably by the role, at CBR, of Ficus sp. in howlers’ diet, as it was highly selected and represented half of all feeding events. Chesson’s electivity index showed that howlers in fragments selected 12 of the 16 species used for feeding; while in CBR, they selected 9 of the 10 species used for feeding. At both types of forests, feeding trees were taller and were greater in diameter than non-feeding trees. Trees exploited by howlers for feeding have commercial dimensions and most of these species are commercially logged. As a result, in fragments and logged forests, howlers have to face the lack of continuity in the canopy and the loss of many vital trees for feeding. We expect howler monkeys to survive in fragmented sites if tree species important in their diet are conserved. [ABSTRACT FROM AUTHOR]

In summary, forest fragment age is an important explanatory variable for capuchin and howler density (higher densities were found in older areas of forest), whereas it makes no contribution to explaining the density of spider monkeys. The presence of evergreen forests in ACG is also important for explaining the absolute density of all three species, as there were higher densities in fragments containing evergreen forest. Transects where water was available in the dry season had higher capuchin densities; water availability appears to be more important for this species than for the spider monkeys and howlers. Forest fragment isolation and size made little contribution to explaining the density of any primate in ACG, probably due to the large size of forest fragments surveyed. Based on these findings, we conclude that older fragments of forest with dryseason standing water, and a substantial amount of evergreen forest should be preferentially protected to enhance the conservation of white-faced capuchins, black-handed spider monkeys, and mantled howlers in Costa Rica. [ABSTRACT FROM AUTHOR]

A Central American black howler population in Monkey River, Belize, was monitored from May of 1999 to May of 2001 and was determined to have similar small group size with multi- and single-male groups. Fifty-three monkeys lived in 8 social groups in a 52-ha study area (population density 102 individuals/km2) that is part of the larger continuous forested area of the Monkey River watershed. On October 8, 2001, the study area was severely damaged by Hurricane Iris, a category four storm that resulted in complete defoliation of the forest along with severe structural damage to those trees not snapped or uprooted. When the area could be accessed again in February 2002, it was determined that the population had dropped by 42%, with 31 monkeys in 5 social groups inhabiting the study area. While initially it was hoped that the population would stabilize at this level, subsequent monitoring through May of 2004 (29 months post hurricane) has revealed a slow but steady decline in the population through the apparent dispersal of whole or parts of social groups, and poor infant survival. We hypothesize that a combination of nutritional and social stress interacting with increased parasite loads (and possibly increased predation) is leading groups and individuals to leave the area, moving west along the river in search of better habitat that is not available. The watershed forest fragment (approximately 100 km2) was equally damaged by the storm from the southern highway of Belize to the coast, leading us to believe that survival of the animals leaving the study site is unlikely. We are currently investigating phytochemical, hormonal, and parasite contributions to the continued decline of the Monkey River howler monkey population following hurricane Iris. [ABSTRACT FROM AUTHOR]

Until now, little information was known about demographic features of the regionally endemic black howler populations living in large tracks of tropical forests. Here, we report results from population surveys conducted in eight extensive forests sites (>8.5 km2) in Mexico and Guatemala. We also surveyed the black howler population in the fragmented landscape bordering two of the extensive forest reserves. Based on the 120 troops encountered in the extensive forest sites, mean troop size was 6.57 (SE = 1.20) individuals (range 2–12 individuals). Troops had most commonly a multimale-multifemale social structure, with two adult males and two adult females being the most common. Population densities ranged from 12.7 to 44.1 individuals/km2. Mean troop size and composition were not correlated to population densities. For the two fragmented landscapes bordering the extensive forests, mean densities in forest fragments were, on average, five times higher than in extensive forests. Mean troop composition was not significantly different between forest fragments and extensive forests, but data suggest a tendency of fewer males in troops living in forest fragments. Long-termmonitoring in extensive forests is necessary to document variability in population dynamics and to make adequate assessments of the consequences of fragmentation on demography, behavior, and life history of A. pigra. [ABSTRACT FROM AUTHOR]