Cross-site comparison studies of behavioral variation can provide evidence for traditions in wild species once ecological and genetic factors are excluded as causes for cross-site differences. These studies ensure behavior variants are considered within the context of a species' ecology and evolutionary adaptations. We examined wide-scale geographic variation in the behavior of spider monkeys (Ateles geoffroyi) across five long-term field sites in Central America using a well established ethnographic cross-site survey method. Spider monkeys possess a relatively rare social system with a high degree of fission-fusion dynamics, also typical of chimpanzees (Pan troglodytes) and humans (Homo sapiens). From the initial 62 behaviors surveyed 65% failed to meet the necessary criteria for traditions. The remaining 22 behaviors showed cross-site variation in occurrence ranging from absent through to customary, representing to our knowledge, the first documented cases of traditions in this taxon and only the second case of multiple traditions in a New World monkey species. Of the 22 behavioral variants recorded across all sites, on average 57% occurred in the social domain, 19% in food-related domains and 24% in other domains. This social bias contrasts with the food-related bias reported in great ape cross-site comparison studies and has implications for the evolution of human culture. No pattern of geographical radiation was found in relation to distance across sites. Our findings promote A. geoffroyi as a model species to investigate traditions with field and captive based experiments and emphasize the importance of the social domain for the study of animal traditions.

Studies of laterality of hand function in chimpanzees (Pan troglodytes) have the potential to tell us about the origins of handedness in Homo sapiens. However, the data are confusing, with discrepancies present between studies done in the field and the laboratory: the former show wild chimpanzees to be unlateralised at the population level, while the latter show captive chimpanzees as lateralised at the population level. This study of 26 semi-free ranging chimpanzees of Chester Zoo, UK, aimed to investigate a situation between the wild and captivity and provided ethological data for 43 categories of spontaneous manual use and 14 categories of tool use. Other variables recorded were subordinate hand activity, whether the subject was arboreal or terrestrial, and the identity of the subject. Using switching focal subject sampling, 23,978 bouts of hand use and 1,090 bouts of tool use were recorded. No population-level handedness was present for manual non-tool use activities in the naturalistically housed chimpanzees of Chester Zoo in a similar way to studies of wild chimpanzees. However, about half of the individuals were lateralised to one side or the other for the foraging behaviours of pick up, eat, and pluck. Using a modified version of McGrew and Marchant's (1997) Laterality Framework, these results are comparable to some wild and captive populations for similar foraging tasks. Bimanuality was rare and thus prevented comparison with captive experimental studies that have reported population right handedness. Behaviour involving contact with water elicited stronger lateralisation. Chester chimpanzees were more likely to exhibit hand preferences for manual tasks with increasing age but there were no effects of sex or rearing history on hand specialisations in adult individuals. Lateralisation was biased in tool use, which evoked significant left hand preferences in half the individuals, with no effect of age. Results are discussed comparatively with reference to methodological and developmental issues. Longitudinal studies of hand use are needed to increase our understanding of laterality of hand use in chimpanzees.

The main objective of this study was to estimate the population density and demographic structure of spider monkeys living in wet forest in the vicinity of Sirena Biological Station, Corcovado National Park, Costa Rica. Results of a 14-month line-transect survey showed that spider monkeys of Sirena have one of the highest population densities ever recorded for this genus. Density estimates varied, however, depending on the method chosen to estimate transect width. Data from behavioral monitoring were available to compare density estimates derived from the survey, providing a check of the survey's accuracy. A combination of factors has most probably contributed to the high density of Ateles, including habitat protection within a national park and high diversity of trees of the fig family, Moraceae. Although natural densities of spider monkeys at Sirena are substantially higher than those recorded at most other sites and in previous studies at this site, mean subgroup size and age ratios were similar to those determined in previous studies. Sex ratios were similar to those of other sites with high productivity. Although high densities of preferred fruit trees in the wet, productive forests of Sirena may support a dense population of spider monkeys, other demographic traits recorded at Sirena fall well within the range of values recorded elsewhere for the species.