Doctoral Dissertation Improvement: An Experimental Analysis of Alarm Calling Behavior in Wild Tufted Capuchin Monkeys (Cebus apella)

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With funding from the National Science Foundation, Dr. Charles Janson will conduct one year of fieldwork to investigate the evolution of alarm calling behavior in tufted capuchin monkeys in Iguazu National Park in northeastern Argentina. Alarm calls, vocalizations given by prey species when a predator is detected, are found in many group-living animals. These calls have long been of interest to evolutionary biologists because their existence seems to contradict evolutionary theory; an individual who produces a vocalization while in the presence of a predator is more likely to be detected by the predator than is a silent individual. Several hypotheses, falling into three main categories, have been put forth to explain how alarm calls can be maintained in a population. First, an alarm may benefit the caller directly (e.g., if alarms deter the predator from attacking the caller). Second, an alarm may benefit relatives of the caller by alerting them to the presence of a predator. Finally, individuals may be able to use the calls in the absence of predators to manipulate the behavior of other group members (e.g., to usurp food resources). Although hypotheses falling into these categories have been tested in a number of birds and mammals, studies of alarm calls among primates are scant. The aim of this study is to be the first to extensively test multiple hypotheses for the evolution of alarm calling among wild primates and to examine whether or not alarm calls are used to usurp resources from other group members. In order to examine theses aspects of alarm calling behavior, three types of experiments will be conducted. First, models of predators of capuchin monkeys (including ocelots, hawk-eagles, and snakes) will be used to determine the reaction of the monkeys upon detecting predators. Second, recordings of alarm calls will be played back to live hawk-eagles in an avian rehabilitation center in order to determine if the production of alarm calls deters the predator from attacking a caller. Third, platforms suspended from tree branches and filled with bananas will be used to determine if the amount and distribution of food affects the propensity of capuchin monkeys to produce alarm calls in the absence of a predator. The intellectual merit of this study will be a better understanding of the factors that allowed for the evolution and maintenance of alarm calls among primates. The data which will result from this project are important because of both the widespread interest in alarm calling among evolutionary biologists and the notable absence of such data for primate species. The broader impacts of the study are that it will increase what is known about a widely noted but under-investigated aspect of primate behavior. In addition, this project will contribute to the training of a graduate student (the co-PI) in primate behavior as well as to the training of undergraduate and post-graduate students from the host country. Argentine field assistants will be given the opportunity to conduct research with the study animals for their undergraduate theses and the co-PI will have the opportunity to serve as the thesis advisor or co-advisor for these projects. Finally, the experiments conducted at the avian rehabilitation center will provide much needed funding for conservation efforts in what is the only remaining large continuous fragment of the Upper Parana Atlantic Forest.