by Angela Peetz Society of Tropical Ecology 2001 ABSTRACT Bearded Sakis (Chiropotes satanas) are specialized frugivores with a large proportion of seeds in their diet. Studies in Brazil and Surinam showed that these primates prefer high tropical forests. Other than living in medium to large multi-male-multi-female groups, little is known about the social behavior and organization of the genus. The aim of this study was to investigate the extent to which ecological parameters influence behavioral strategies in a group of Chiropotes satanas chiropotes at the northern limit of the species' geographical distribution. Feeding ecology, activity budget, and ranging behavior were related to food abundance and monthly variation in the productivity of the habitat. Furthermore, social behavior patterns were considered in order to reveal aspects of the social organization of the Bearded Saki group. The study was carried out at one of the field sites of the "Proyecto de Primatologia Ecologica de Guayana," which was located on an island of about 180 ha (7°21'N, 62°52'W) in Lake Guri in Eastern Bolivar State, Venezuela. The climate was characterized by a distinct dry season. Behavioral data on the C. s. chiropotes group were recorded over 15 months employing 5-minute instantaneous scan-sampling and ad lib. observations on five consecutive days, with c. 50 hours of observation per month. Data on the habitat were collected by quantifying the plant species composition, and by monitoring phenological cycles to assess peaks in relative productivity. The floristic inventory (total 1.5 ha) amounted to 983 woody plants > 10 cm dbh, representing 128 species in 40 families. Canopy height averaged 9 m, with only 1.5 % of the trees attaining heights of 20 m or more. The species Importance Value indicated no leading species. Phenological data showed production of young leaves, flowering, and fruiting throughout the year. During the dry season, however, almost a quarter of the sample was fully defoliated. With regard to the distinct dry season, maximum tree height, and the striking presence of lianas in the forest, as well as the lack of a leading species, the forest type was classified as a "transitional semi-deciduous tropical moist forest." During the whole study, the Bearded Sakis exploited at least 100 plant species for food. Fruit was the primary food resource during every month, amounting to an annual average of 92.3 % of all feeding records. Seeds accounted for the largest quantity of food items derived from fruit, with an annual average of 50.7 %, and were the major food source during the dry season months. Flowers were 0.9% of records, vegetative material 2.5%, and items of the second trophic level 3.9 %. Pradosia caracasana (Sapotaceae) was the most important food plant, with 37.0% of the annual feeding records, while its parasite Oryctanthus alveolatus (Loranthaceae) accounted for another 18.6%. Daily activity of the study group started before or with first light and ended well before sunset. Feeding comprised the largest part of the annual activity budget (37.0 %), and was most frequent in the dry season. Foraging was recorded as 10.1% of activity, traveling 18.7%, and resting 21.4%. Other behavior patterns accounted for 12.8%. The study group used an area of 122.25 ha, but 50% of all utilization was recorded in only 15.75 ha. The annual average daily path length amounted to 1.6 km, with daily path lengths ranging from 0.5 to 2.7 km. Ranging behavior was influenced by the availability of Pradosia caracasana fruit. All social interactions with social resting (5.8%), social play (5.6%), allogrooming (5.0%), and other behavior patterns of a sexual, associative or agonistic context comprised 17.9% of the groups annual activity budget. The amount of social interactions decreased when the proportion of seeds in the monthly diet was high, whereas it increased when the Bearded Sakis fed on juicy fruits. While the amount of grooming activity remained almost constant throughout the study period, play behavior distinctly decreased during seed-feeding months. Considering the high amount of social interactions, and some apparently ritualized behavior patterns, strong ties between individuals seem to be prevalent in the social organization of the study group. Affiliative behaviors directed at the breeding male, as well as his involvement in agonistic interactions and appeasement behaviors, indicated a male dominance. Since there was only one adult male in the Bearded Saki group, behavioral data on groups with more adult males are needed to distinguish the breeding system of C s. chiropotes. The Author After half a year of voluntary work at the "Max Planck Institut fur Verhaltensphysiologie" in Seewiesen, Germany, Angela Peetz began to study biology at the University of Bielefeld, Germany. She focused on ecology and behavior of birds and mammals. Starting in 1988, Angela Peetz joined the "Proyecto de Primatologla Ecologica de Guayana" in Estado Bolivar, Venezuela, run by the late Prof. Dr. Warren G. Kinzey (City University of New York) and Prof. Dr. Marilyn A. Norconk (Kent State University). For her M.Sc. thesis Dr. Peetz studied the behavior of a group of red howler monkeys Alouatta seniculus stramineus. Subsequently Prof. Kinzey invited her to continue research within his project and to work on the ecology and behavior of Bearded Sakis Chiropotes satanas chiropotes for her Ph.D. dissertation. CONTENTS Abstract 7 Resumen 8 Resumo 10 Zusammenfassung 12 Acknowledgments 15 1. Introduction 17 Introduction to the Species 18 Approach and Aims of the Study 20 Study Site and Climate 22 The Primates of Lake Guri 24 General Methodology 24 2. Habitat 27 Introduction 27 Floristic Composition 27 Methods 27 Results 29 Plant Phenology 40 Methods 40 Results 41 Discussion 44 3. Feeding Behavior 50 Introduction 50 Methods 50 Results 52 Dietary Composition - Plant Resources 52 Dietary Composition - Animal Resources 62 Monthly Variation in Feeding Behavior 63 Potential Food Competitors 74 Discussion 78 4. Activity Budget 85 Introduction 85 Methods 85 Results 87 Discussion 98 5. Ranging Behavior 104 Introduction 104 Methods 104 Results 105 Habitat Use 105 Movement 113 Effects of Food Choice on Ranging Behavior 118 Discussion 119 6. Social Behavior and Organization 124 Introduction 124 Methods 124 Results 125 Social Interactions 125 Predator Avoidance 139 Infant Development 139 Discussion 140 References 147 Appendices 158 Index 167 WHERE TO ORDER: GTOE Zoological Research Institute and Museum of Zoology Adenauerallee 160 D-53113 Bonn, Germany Price: EURO 55.00 (Add Euro 5.00 for handling and shipping charges outside Europe) Make checks payable to GTOE, Bonn.
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