With primate populations losing 125,140 km2 of habitat annually most populations exist either in isolated, scattered protected areas, or in unprotected areas facing pressures from an increasing human population. Cercopithecine monkeys, a subfamily of small, frugivorous monkeys, are now found only in tiny forest fragments and a few national parks and forest reserves throughout West and East Africa. Scientists have recognized that little progress has been made towards providing scientific information that managers can use in the conservation of this subfamily. For example, while it has been suggested that weather, disease, infanticide, and food resources may all act to regulate primates populations, little is known about the specific conditions necessary for a species to survive and prosper. Food resources have been argued to be the most common limiting factor for most species, yet little is known about how food quantity and quality interact to determine the size and distribution of primate populations. This is particularly true for frugivorous primates since fruit, unlike leaves, is typically low in protein, minerals, and lipids, making it difficult to maintain a balanced diet. Therefore, this study will use redtail monkeys in Kibale National Park, Uganda to investigate the relationship between nutrient intake and availability, reproduction, and population densities. In addition, it will determine if nutritional factors are responsible for reduced population densities of redtail monkeys in heavily logged areas. Three focal groups have been identified in the heavily logged and unlogged areas to: 1) quantify and compare seasonal nutrient intake of groups between areas and to examine relationships between nutrient availability and intake, 2) compare the relationship between nutrient intake and reproduction between groups and correlate nutrient intake and availability with reproductive rates, timing, and infant survival, and 3) identify behavioral responses to changes in seasonal nutrient availability and intake. In addition, nutrient intake and behaviors will be correlated with group size across all six groups. Finally, existing data on redtail population densities and diets across six habitats within Kibale will be used to test for correlations between nutrient availability, key food resources, and redtail population densities. This will be the first study to explicitly examine the role of nutrition in population regulation of frugivorous primates and one of only a few to quantify the mechanisms by which habitat disturbance affects primates. The results of this study have implications to our understanding of the diets and nutrition of extinct and extant primates and hominids, the role of nutrition in population regulation, and the conservation and management of frugivore populations. By identifying the tree species needed to support high densities of redtail monkeys, current and future habitat restoration and protection plans will have the information necessary to design appropriate management strategies.