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A total of 54 free-ranging monkeys were captured and marked in Santa Rosa National Park, Costa Rica, during May 1985, and an additional 17 were captured during March 1986. The animals were darted using a blowpipe or a CO2 gun. The drugs used were Ketaset, Sernylan and Telazol. Ketaset was effective for Cebus capucinus but unsuccessful for Alouatta palliata and Ateles geoffroyi. Sernylan was successful for A. geoffroyi and A. palliata but is no longer commercially available. Telazol proved to be an excellent alternative capture drug for both A. palliata and A. geoffroyi.

The feeding patterns of three neighboring groups of Cebus capucinus were documented over a 3-year period in Santa Rosa National Park, Costa Rica. We describe the diets of the three groups and examine whether dietary differences between groups could be attributed to environmental differences in food abundances, to differences in the profitability of what was available or to learned local traditions. Diets were variable among groups; group A primarily ate fruit (81.2% of feeding time) and spent little time eating insects (16.9%), while group C was more heavily reliant on insects (44.3%) and ate less fruit (53.0%). Group B had a diet that was somewhat intermediate (69.8% fruit, 29.0% insects). By measuring the densities of all major plant foods, we were able to determine that many of the dietary differences between groups could not be attributed to simple measures of food abundance, but we could not distinguish between the food profitability hypothesis and local tradition hypothesis.

A long-term study of two groups of white-faced capuchins (Cebus capucinus) in Santa Rosa National Park in Costa Rica provides evidence of unusually high levels of vertebrate predation compared to those reported in other field studies of Cebus. The hunting techniques for different prey types are described, and several questions concerning vertebrate predation in primates are addressed. Why is there variation between individuals and between groups in the rate of predation? Why do males hunt more than females? Previous hypotheses to explain hunting in Old World primates are applied to this Neotropical example. Finally, I argue that successful vertebrate predation can readily arise in species like Cebus, which are characterized by opportunistic foraging patterns, manipulative and cognitive skills and well-developed techniques for locating and subduing invertebrate prey.

Lifetime reproductive success, measured by the number of offspring surviving to age five, varied from 0 to 10 in a group of 33 provisioned female Japanese macaques. Of the three contributors to reproductive success, the number of reproductive years, fecundity per year and survivorship of offspring to reproductive age, the first accounted for two-thirds of the variation. Fecundity per year and survivorship were negatively correlated, indicating reproductive costs of reducing interbirth interval. No other demographic measure used, nor the behavioral measure 'dominance rank', significantly correlated with lifetime reproductive success or its components. Age-specific changes in fecundity and infant survival were not found for this sample, neither could cessation of reproduction, even in very old females, be demonstrated.