The theory of optimal foraging predicts that animals in nature will select a diet that balances the energy consumed through feeding with energy expended in such activities as self-maintenance, socializing, and obtaining food. Although this theory is an excellent framework for studying the feeding patterns of predators, optimal-foraging theory needs more careful evaluation when considering the ready adaptability of some primates, such as the rhesus monkey (Macaca mulatta), to extremely diverse habitats and food resources. Through social learning, macaque monkeys of several species have developed unique feeding adaptations. On Koshima Island in Japan, the monkeys (Macaca fuscata) carefully monitor the tidal movements and have learned to remove and eat limpets when these animals have relaxed their muscles under changing tidal pressure. On Cayo Santiago, an island off the coast of Puerto Rico, preliminary observations indicate that rhesus monkeys may also have developed specific feeding techniques to harvest marine organisms. These monkeys are particularly suitable subjects for assessing learned behavior patterns in relation to family relationships, as the lineage of individual monkeys is known since the 1930s. Does optimal-foraging theory account for these unique feeding adaptations? Drs. Marriott and Tobach will carry out a pilot study that will provide basic information for the development of two future long- term projects on the feeding behavior and ecology of rhesus monkeys. The first is an initial study of the feeding ecology of rhesus monkeys on Cayo Santiago across the yearly seasons. The second is a preliminary descriptive study of feeding on marine organisms within the contex of the overall feeding ecology. The objective of this project is to collect quantitative information across the yearly vegetational seasons on 40 identifiable rhesus monkeys of both sexes. All food items will be sampled, identified, and combusted to determine gross energy. Continuous behavioral observations will include data on food-collection, -preparation, and social aspects of feeding. Estimates of energy expenditure and input will be calculated to develop a bioenergetic evaluation of feeding patterns. Thus, Drs. Marriott and Tobach will describe marine feeding adaptations of the Cayo Santiago rhesus monkeys and will evaluate these feeding adaptations in terms of optimal-foraging theory and the social status and lineage of individual animals.
