Social Conventions, Sexual Selection, and Acoustic Signals in Wild Brown Capuchins

University Of Florida, Gainesville FL

Investigators

Abstract

The capacity to combine objects and employ objects as tools is considered one of the major achievements of our species and figures deeply in our mythological, philosophical, cultural, and academic explanations for the evolution of human intelligence and behavior. Many researchers hold that object manipulation, language, social skills, and brain structure are been linked in human evolution. For the past 40 years capuchins monkeys, New World primates in the genus Cebus, have often been suggested as models for the evolution of intelligence and tool use in humans. Among primates, only only chimpanzees and humans exceed capuchins in the frequency, complexity with which objects are combined and manipulated. Although suggestive observations come from capuchins in captivity, scant evidence from wild populations is available to test hypotheses as to why exceptional manipulative abilities can be advantageous in natural settings and how individuals acquire these skills. Brown capuchins (Cebus apella) in the Central Suriname Nature Reserve (CSNR) use complex object manipulation at the highest rates yet documented among wild capuchins. More specifically, male capuchins at CSNR employ an array of object combinations and manipulations labeled as percussion: striking sticks or hard fruit against hard surfaces and breaking off tree limbs. Percussion generates mechanical (non-vocal) acoustic sounds that transmit farther and more reliably in this densely forested environment than social signals based on visual displays. Preliminary observations suggest that capuchins evaluate the acoustic structure of the noises males produce in percussion as honest indicators of male strength and vigor important in male-mate competition and female mate choice, i.e., the stronger the male percussing, the louder the noise. This research project evaluates hypotheses about (1) the functions of brown capuchins' percussive behavior, focusing on the relative benefits accruing in sexual selection versus foraging, and (2) the expression of percussion in relation to an individual's developmental status and social circumstances. Whatever the findings, the theoretical implications are important and encompass anthropology, biology, ecology, and psychology. Percussive behavior will be most fully understood against the distinctive ecological background of capuchin society at CSNR. First, the biota of the Guianan Plateau is characterized by extremely low energy and nutrient flow relative to other Neotropical regions. Second, these regional ecological characteristics are compounded by previously unsuspected landscape earthworks by pre-Columbian Amerindians populations in the area now encompassed by the CSNR. Recent exploratory work by Boinski and colleagues confirms that pervasive archeological features are present in CSNR; these sites covary with the bamboo and liana forest habitats preferentially used by capuchins. This primate and community ecology research program has been ongoing in the CSNR since 1998 and remains the only multi-year ecological project within Suriname's forested interior since the end of violent civil uprisings (late 1970's - early 1990's). Boinski and her team work with biologists, educators, and wildlife and conservation officials of Suriname, international NGOs, and Peace Corps. Long-term supportive relations have developed between Surinamese Park Service and the research team, leading to educational and conservation outreach and contributions to the scientific infrastructure of Suriname by this project far beyond the immediate research products. Educational videos produced from research tapes will be made freely available on the web. The CSNR project is engaging the Surinamese with provocative questions about the cultural and biological significance of their matchless forests at a moment in history when national and foreign interests seek to expand economic exploitation of these same forests.