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No Easy Answers: Male-Male Relationships of Surinamese Brown Capuchins as a Result of Complex Interactions and Multiple Variables

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No Easy Answers: Male-Male Relationships of Surinamese Brown Capuchins as a Result of Complex Interactions and Multiple Variables
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KAUFFMAN, LAURIE ( Author, Primary )
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2008

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Animal grooming ( jstor )
Ecology ( jstor )
Female animals ( jstor )
Mating behavior ( jstor )
Monkeys ( jstor )
Personal hygiene ( jstor )
Predators ( jstor )
Primates ( jstor )
Social behavior ( jstor )
Trucks ( jstor )

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University of Florida
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University of Florida
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Copyright Laurie Kauffman. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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8/31/2007
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436097587 ( OCLC )

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NO EASY ANSWERS: MALE-MALE RELATI ONSHIPS OF SURINAMESE BROWN CAPUCHINS AS A RESULT OF CO MPLEX INTERACTIONS AND MULTIPLE VARIABLES By LAURIE KAUFFMAN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS UNIVERSITY OF FLORIDA 2004

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Copyright 2004 by LAURIE KAUFFMAN

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Dedicated to my parents and all my teach ers and friends at Rosati and Grinnell

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ACKNOWLEDGMENTS This thesis would not be possible without the assistance and patience of my supervisory committee, Drs. Sue Boinski, Colin Chapman and David Daegling. I especially have to thank Sue Boinski for giving me the opportunity to do research in Suriname, access to her data, and for her continuing advice and encouragement. Without her, this thesis would not at all have been possible. I also must thank Erin Ehmke for many discussions about monkey behavior, life, and her helpful hints and support through the entire graduate school process. Thanks also go to my fellow graduate students in the Department of Anthropology for their friendship and willingness to share their knowledge on anything from capuchin sexual dimorphism to the use of the master’s thesis template. Finally, I thank my mom and dad, my brothers, and Rick for their on-going faith and never-exhausted support. iv

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TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES............................................................................................................vii LIST OF FIGURES.........................................................................................................viii ABSTRACT.......................................................................................................................ix CHAPTER 1 INTRODUCTION........................................................................................................1 Troop Defense..............................................................................................................7 Relatedness...................................................................................................................8 Life History Variables..................................................................................................8 Multi-Male Groups in Brown Capuchins.....................................................................9 2 METHODS.................................................................................................................10 Study Site....................................................................................................................10 Study Animals............................................................................................................10 Sampling Methods......................................................................................................11 Study Troop................................................................................................................12 3 RESULTS...................................................................................................................13 Grooming....................................................................................................................13 Male-Male Aggression...............................................................................................15 Male-Male Displacements..........................................................................................15 Male Cooperation in Intergroup Encounters..............................................................15 Male Cooperation in Predator Defense.......................................................................16 Alpha Male Tolerance of Copulations........................................................................16 v

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4 DISCUSSION.............................................................................................................17 Group Size and Composition......................................................................................17 Troop Defense in Exchange for Copulations and Grooming.....................................18 Philopatry....................................................................................................................19 Further Comparisons..................................................................................................20 LIST OF REFERENCES...................................................................................................26 BIOGRAPHICAL SKETCH.............................................................................................33 vi

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LIST OF TABLES Table page 1 Comparison of Raleighvallen Cebus apella to those at other sites .....................17 2 Comparison of male-male relationships across species......................................21 vii

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LIST OF FIGURES Figure page 1 Males as groomer or receiver...................................................................................14 2 Grooming bouts by dyad..........................................................................................14 viii

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Arts NO EASY ANSWERS: MALE-MALE RELATIONSHIPS OF SURINAMESE BROWN CAPUCHINS AS A RESULT OF COMPLEX INTERACTIONS AND MULTIPLE VARIABLES By Laurie Kauffman August 2004 Chair: Sue Boinski Major Department: Anthropology Despite early primatologists’ concentration on male aggression as the driving force behind primate social strategies, little comparative work has been done on the substance of male-male relationships. Prevalent theory argues that males in the same group will be intolerant of each other’s mating attempts as paternity, unlike food, cannot be shared readily. Male-male relationships are also expected to be affected by many variables such as need for troop defense, philopatry, genetic relatedness, and life experiences. This paper represents a critical consideration of the myriad factors that influence male-male social behavior. Long-term data collected on brown capuchins (Cebus apella) at Raleighvallen in the Central Suriname Nature Reserve indicate that co-resident adult males in Suriname exhibit stronger male-male affiliation and tolerance than reported elsewhere. Males in Raleighvallen exhibit higher rates of male-male grooming ix

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and lower rates of aggression than suggested by studies of brown capuchins in Peru and Argentina. Furthermore, the comparison of brown capuchins with other species emphasizes the great variability and flexibility found in male-male social behavior, and the need for additional descriptive data and a more dynamic theoretical approach regarding this subject. x

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CHAPTER 1 INTRODUCTION Male primates were the main focus for the first generation of scientists studying primate behavior and aggressive behavior by males was seen as the central force in primate groups (Washburn & Hamburg, 1968; Popp & DeVore, 1979; also see Fedigan, 1992). Wrangham (1980) built upon models that integrated female behavior (Trivers, 1972; Emlen & Oring, 1977; Vehrencamp, 1983) to present a theory of social organization in which females depend on food as their limiting resource, and males depend on females. Females were thought to adjust their social behavior to enhance their access to food resources, and in turn males adjust their behavior to the females’, resulting in sex specific tactics. As the importance of ecology to primate behavior became more evident, females were brought to the fore because of the theorized close tie between their behavior and food resources. Since male social behavior was biased towards gaining access to females, female-female interactions and male-female interactions were studied, but not much mention was made of the subtleties of male-male social behavior beyond dominance and aggression (de Waal, 1987; Fedigan, 1992). This reversal of emphasis continued until the early 1990’s, when studies of males made a brief surge, but then returned to their previous obscurity (see Kappeler 2000; van Schaik and van Hooff 1994). Even much of this later research on male primates was limited to the number of males living in a group as opposed to focusing on male-male social relationships (see Ridley, 1986; van Schaik & Horstermann, 1994; Nunn, 1999; Cords, 2000; Heymann, 2000; Mitani et al., 2000; Kappeler, 2000). 1

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2 In this paper, I will explore the applicability of current theory, which predicts the character of male-male relationships based on numerous other factors, through a comparison of research on brown capuchins in Suriname with other populations of brown capuchins and other primate species. In this first section, I will explore the predictions about male-male social behavior that arise from current theory. I will present a summary of the costs and benefits of living in a multi-male group versus a single male group, discuss the character of male-male relationship expected to arise under different circumstances, and finally outline the main factors expected to contribute to differences in male-male relationships between multi-male groups. Most primates live in groups which consist of one or more breeding males and one or more breeding females (van Schaik, 1983). According to current theory, the advantage for a male living in a one male group is that he can monopolize the females and increase mating success (Emlen & Oring, 1977). Less obvious is the answer to the question: what is the benefit of living within a multi-male group? An investigation of the costs and benefits of living within a multi-male group can be approached from two sides: that of the perspective of the dominant male and that of the perspective of the subordinate male. In a multi-male group the dominant male allows other males proximity to the females of his group which may decrease his mating success. The subordinate male in the group may be participating in group defense or incurring other costs, but may not be gaining maximum reproductive success. Some researchers (Cowlishaw & Dunbar, 1991; Cowlishaw & O'Connell, 1996; van Hooff, 2000) have discussed why a dominant male would allow other males in the group and most agree that multi-male groups arise when the dominant male cannot monopolize the females. The literature suggests a number of

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3 reasons why this may occur (Cowlishaw & Dunbar, 1991; Cowlishaw & O'Connell, 1996; van Hooff, 2000): 1. females come into estrous simultaneously, and the alpha male cannot mate with all of them 2. females are dispersed to such an extent that the resident male cannot monitor them continually 3. number of females is simply to large to be constantly monitored 4. the number of additional males near the group is too large to monitor 5. the sex ratio is skewed 6. there is little sexual dimorphism Once a multi-male group exists the character of the relationships between males in the group is not necessarily predetermined. There are two main options predicted for the character of male-male relationships, depending on the circumstances of the group. First, males may be intolerant towards other males in the group, as exhibited through spatial isolation of males from one another, aggression (lunges, chasing, threats, biting), interference by the dominant male in copulations of subordinate males, and limited access to food for the subordinate males (van Schaik & van Hooff, 1983; Janson, 1985b; Janson, 1990; Janson, 1996). Second, the males in the group may be tolerant, affiliative, or even cooperative towards each other. Tolerant males will not exhibit aggression towards one another, nor interfere overtly in another males copulation attempts(Izawa, 1980; cf: Janson, 1996). Affiliative males will spend most of their time in proximity to one another, and will often groom or make contact in another way (Hill & van Hooff, 1994; Strier et al., 2002). Males may also cooperate, which is defined as two or more individuals acting together to gain something for either to gain benefits that are unavailable if either were acting alone (de Waal & Harcourt, 1992).

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4 The first category of male-male relationships expected in multi-male groups is readily explained. If males benefit most from monopolizing females, then male-male relationships are expected to be characterized by intolerance. As paternity cannot be shared males will be intolerant of one another unlike females who can share resources (Crook & Gartlan, 1966). Therefore multiple males should exhibit aggression towards each other and low levels of affiliation. Females benefit from the affiliative bonds that grooming suggests, as by means of bonds built through grooming, females can cooperate to gain access to food often resulting in more grooming between females than between males (Wrangham, 1980). Males, who cannot share their limiting resource as easily, will have less affiliative relationships (Trivers, 1972; van Hooff & van Schaik, 1994). Aggression between male group members will arise when the dominant male is unable to exclude subordinate males. In these situations the dominant male will be aggressive to other males’ mating attempts and try to limit access to estrous females. If the females in the group are rare or spatially isolated there should be more intragroup aggression (Terborgh & Janson, 1986) as the alpha male will be able to monopolize the females or because they are harder to gain access to and are therefore a scarcer resource. Van Schaik and van Hooff (1983) state that multiple males may occur in groups, but that the subordinate males will remain far away from the dominant male. Aggression over a resource will increase as the benefit of exclusive access to that resource increases (Janson, 1996). Higher aggression would be expected over access to females as mating success is the most direct road to fitness. The dominant male in the group should not want subordinate males in the troop and should therefore act intolerant towards them.

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5 In contrast, current theory is less able to explain situations in which males will be tolerant. There are three proposed situations in which male-male interactions may be more tolerant than intolerant. Males may need the support of subordinate males to maintain access to the females (van Hooff, 2000), the possible cost of injury incurred by males during aggression is too great (Eisenberg et al., 1972; Preuschoft et al., 1998) or the males in the group are related and cooperate to increase their inclusive fitness (Maynard Smith, 1964). If outgroup males or predators are a threat to the females in the troop, the dominant male may be more tolerant of subordinate males in the troop. He may also allow the subordinate male access to females and food resources in return for assistance in troop defense. (Sussman & Garber, 1987; Goldizen, 1989; Noe, 1992; van Schaik & Horstermann, 1994; Koenig, 1995; Davies, 2000). When subordinate males are needed for the support they contribute to the alpha male, the subordinate males have “leverage” and may receive some benefits in return for their cooperation (van Hooff, 2000). These benefits may include access to females or important food resources (Terborgh & Janson, 1986) as well as the opportunity to live in the group and be more protected from predators (van Schaik & Horstermann, 1994). Males in multi-male groups may also be affiliative because the cost of aggression is too great (Eisenberg et al., 1972; Preuschoft et al., 1998). If the males are of similar size and condition, it could be unlikely that they will be able to fight the other male and win, and in addition, could suffer dangerous injuries. In these cases the threat of injury is dire enough that males will be tolerant or affiliative to avoid the high costs that they could incur through aggressive behavior. The fact that aggression is not often observed, may not mean that it is not important (Silverberg & Gray, 1992).

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6 Genetic relatedness can affect male-male relationships. Males might be more affiliative if they are related to other males in the group (van Schaik & van Hooff, 1983). They could also have different within group interactions depending on their genetic relationship with one another. Many tolerant multi-male groups are found in species with male philopatry (Strier, 1992; Hill & van Hooff, 1994; Strier et al., 2000; Watts, 2000) or parallel dispersal; the immigration of more than one related male into a new troop (van Hooff, 2000; Jack, 2003). On the other hand, males in female philopatric societies are often agonistic (Stanford, 1998). In these groups, males move between troops and therefore do not have as stable and long lasting bonds as those that live in male philopatric species (Cords, 2000). The above theories about male-male intragroup relationships demonstrate the vast number of potential factors that can affect these relationships, and the different theories most often presented in order to predict and categorize male-male interactions. Male monopolization of females can be related to number of females, dispersal of females, number of other troops, breeding season, number of males, sexual dimorphism, and relatedness to other males in the troop. As male relationships are based on gaining access to females who are competing for food resources, male-male social behaviors have wide variation across species. Since copulations are a necessary prerequisite to fitness, a male’s behavior is expected to optimize access to as many copulations that will result in viable offspring as possible based on whatever context he finds himself. It is also important to take into account the fact that primates live in long-term social groups, and have detailed experience of their social companions. This factor makes it difficult to predict the characters of male-male relationships without extensive

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7 detailed knowledge of variables such as presence and type of interactions the troop may experience with other troops, the genetic relatedness of individuals within the troop, and the life history of the individuals and the history of their interactions with each other. In addition, as social structure depends on ecological variables (Crook & Gartlan, 1966; Clutton-Brock, 1974; van Hooff & van Schaik, 1994), we expect to see great variation from site to site (Struhsaker, 2000). Also, male-male relationships may not be able to be as simply described as “tolerant” or “intolerant.” Males can be bonded in one arena and compete in another (Stanford, 1998). So far, there are many theoretical predictions, but testing of these predictions is lacking. I will discuss in further detail how each of the above factors are expected to influence male-male interactions, and what other studies have discovered in order to lead up to a description of male-male interactions in one troop of brown capuchin monkeys in Suriname. Troop Defense Intergroup encounters (IGEs) are instances when one groups of monkeys comes into contact (<50 m) with another (Fashing, 2001). These encounters may be aggressive or not. The aggression in these situations may be over a food resource, or may be outgroup males attempting to gain access to the females in the other group (Wrangham, 1980; van Schaik, 1983). In this paper we will be dealing with aggressive intergroup encounters. A dominant male may benefit from having additional males in the group if they assist in defense against outgroup males interested in the group’s females. Perry (1996) found that in white-faced capuchins the need for male-male cooperation in IGEs influences male-male relations. Males with the greatest mating success participated most in intergroup aggression. Others have found that subordinate males in a troop are more likely to have access to females if they assist in defending the

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8 group’s territory (Sussman & Garber, 1987; Goldizen, 1989; van Schaik & Horstermann, 1994; Koenig, 1995). The alpha male’s tolerance of copulations by subordinate males may be payback for their assistance in intergroup aggression, but an alpha male may also allow subordinate males to copulate with females in order to give them the illusion of paternity which may cause them to assist further in the defending the troop, helping both the dominant male and the females in the troop (van Hooff, 2000). Subordinate males may also help defend the troop from predators (Stanford, 1998) for the above reasons. Relatedness Males in the same group may be related either because of male philopatry or because of parallel dispersal. Related males are expected to cooperate more than unrelated males because any costs incurred in the cooperation will be lessened by the fact that they are helping a relative and therefore increasing their inclusive fitness (Maynard Smith, 1964; Morin et al., 1994; but also see Mitani et al., 2000). In general, species in which males are affiliative or cooperative are also species in which the males are related and do not emigrate from their natal troop (Watts, 2000; Strier et al., 2002). Life History Variables Finally, it is important to remember that social interactions are the result of interactions between multiple actors with specific histories (Hausfater, 1975; Emlen & Oring, 1977; Davies, 2000). Individual males’ life histories, and the experiences they have had with each other can also contribute to the relationship of males within the troop. This is one reason why males may be more aggressive in female philopatric species, as male membership in these groups is fluid, males have less of a chance to build relationships with each other and therefore will remain aggressive (van Hooff & van Schaik, 1992; Cords, 2000; Jack, 2003).

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9 Multi-Male Groups in Brown Capuchins Cebus apella live in multi-male groups with male dispersal and male competition for mates is not obvious (Janson, 1984). There is low mating related aggression because the female chooses to mate with the alpha; however, when an estrous female does solicit a subordinate male, the dominant male is intolerant and follows the female to interfere in any copulations (Janson, 1984). Aggression between the alpha and subordinate males is seen, and according to Terborgh and Janson (1986), subordinate males do not cooperate in group defense as the alpha male sires the most offspring. This is in contrast to another capuchin species, Cebus albifrons in which all males sire the same number of offspring and also cooperate (Terborgh & Janson, 1986). Here I compare the characteristics of male-male behavior in Raleighvallen C. apella with those of C. apella at other sites and with other primate taxa. Through this comparison I will explore the drivers of male-male relationships, work towards elucidating the extent of the diversity of these behaviors and demonstrate the importance and need for long-term field studies to test the extensive theory on this subject.

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CHAPTER 2 METHODS Study Site The study site, Raleighvallen (4’N, 56’W), is situated in the 1.6 million ha Central Suriname Nature Reserve (CSNR). The CSNR is located in west central Suriname and is comprised of primary tropical forest. It receives annual average rainfall of 2300 mm (Reichart, 1993). The aerial and terrestrial predator complement of the forest is complete, and no significant hunting or other human disturbance has occurred in this century (Trail, 1987; Reichart, 1993). Eight species of primates are found at the site, Cebus apella, Saimiri sciureus, Cebus olivaceous, Ateles paniscus, Alouatta seniculus, Pithecia pithecia, Chiropotes satanus and Saguinas midas Basic descriptions of the site can be found elsewhere (Fleagle & Mittermeier, 1980; Mittermeier & van Roosmalen, 1981; Boinski et al., 2002; Boinski et al., 2003). Study Animals Brown capuchins (Cebus apella) live in multi-male groups with group membership varying from 10-35 (Janson, 1985a; Hirsch, 2002). They are usually described as female bonded, with a linear dominance hierarchy (Di Bitetti & Janson, 2001). The dominant male of the troop plays a central role, controlling access to food and receives the most mating success (Di Bitetti & Janson, 2001). Female brown capuchins exhibit high mate choice and preferentially mate with the dominant male (Janson, 1984). 10

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11 Sampling Methods Data were collected on one troop of brown capuchins, Cebus apella, from June 2000 through October 2002. Two to eight additional troops were periodically observed in the study site, but this paper will concentrate on the main study troop, Troop A. Data were collected each day from approximately 700-1700 hours, for a total of 3600 hours of observation. Data presented here were collected ad lib (Altmann, 1974; Fragaszy et al., 1992) and all occurrences of male-male grooming, aggression, displacements, cooperation in intergroup aggression, cooperation in predator defense, and copulations were recorded when observed. Definitions of the behavioral categories are listed below: Grooming : one monkey picking through the fur of another. This can be for maintenance and health and is also often considered a sign of affiliation, or a commodity to be traded for another Aggression : one or more individuals threatening, lunging at, biting or chasing another Displacements : can be passive or active and included a male moving away from a foraging spot or other area after being threatened by another, or moving away from a foraging spot upon the approach of another male Cooperation in intergroup encounters : indicated by more than one male behaving aggressively in the presence of or in a direction towards another troop Cooperation in predator defense : two or more males simultaneously threatening or mobbing a predator Copulation : the mounting of a female by a male, including thrusting. Most copulations were easily observable because of the obvious estrous state of the female and her solicitation of the male (Janson, 1984).

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12 The ad lib data collection method may result in some underestimations of behavioral rates, but should not be biased as males are generally in the forefront of the troop and easily observed. Others have found that ad lib data collected on male behavior correlates closely with focal data collected on male behavior (Hausfater, 1975). Study Troop During the study period the study troop, Troop A, was made up of 20 to 35 animals, 3-4 males, 10-14 females and 7-24 juveniles and infants. The troop is well habituated and has been studied continuously for four years, although some preliminary observations began in 1998 (Boinski et al., 2000). Immigration and emigration did occur. In 2001, an older adult male, LX, previously alpha male of another troop, associated with the main study troop for one month. At the end of 2001 and the beginning of 2002 two other males, BL and BR also immigrated into the troop. One natal male, MY, aged from juvenile to subadult over the course of the study, and two others, WY and RY, aged from subadult to adult and transferred out of the troop. No females were observed to change troop residency during this study. Age class definitions used here are the same used by Izawa (1980). For the purposes of this study, both adult and subadult males are considered.

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CHAPTER 3 RESULTS Grooming There were 20 incidents of male-male grooming over the study. In 14 of these, both participants were recognized. Ten of the incidents involved the alpha male, JS, four as groomer and six as receiver. A natal male, MY, who aged from juvenile to adult during the study was the only individual to groom more often than the alpha male. He was involved in six bouts as groomer and two as receiver. Another natal male, RY, who grew from subadult to adult during the length of the study groomed nearly as often as the others, acting as groomer in four incidents. A younger immigrant male, BL, was groomer on two occasions – once to MY and once to JS. BL received grooming in three instances, all from JS (Figure 1). JS was only seen to groom MY, a natal male, or BL, an immigrant male. However, no grooming was observed between JS and LX, an older immigrant male, or between JS and BR, an immigrant male of similar age to BL. JS received grooming from BL, MY and RY. MY groomed JS on four occasions and RY on one. BL groomed MY on one occasion and JS on one. Although BL and BR were in the group at the same time, they were not observed grooming one another. LX, the older immigrant male was receiver once but never groomer, and RK, a juvenile natal male, was receiver once but never groomer (Figure 1). Most male-male dyads participating in grooming participated in only one bout each, except two. The only two dyads to be observed in more than one grooming bout 13

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14 were those of MY and JS and the dyad of JS and BL. MY and JS were observed grooming in four instances, as was the dyad of JS and BL. In the case of MY and JS, MY was always groomer and JS always receiver. In the case of BL and JS, JS was groomer on 5 occasions and BL on one (Figure 2). 01234567JSRYRKMYBLLXMale# bouts Groomer Receiver Figure 1: Males as groomer or receiver 00.511.522.533.544.5JS-RYJS-BLRY-JSRY-LXRK-MYMY-RYMY-JSBL-MYDyad# bouts Figure 2: Grooming bouts by dyad

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15 Male-Male Aggression 17 instances of within group male-male aggression occurred during the study. 14 involved the alpha male as the aggressor. 11 involved an older immigrant male, LX, who was previously alpha male of another troop and later joined the study troop. Six of these consisted of JS, the alpha male, chasing LX away from females in the troop. In the other five, the context was unknown. The six incidents of aggression involving LX were the only instances of aggression over a female observed. Five incidents were over food, and the remaining six are unknown. Three of the incidents involving food were between JS and the natal male MY, one between natal males WY and RY, one between JS and RY and one was between immigrant BR and natal male MY. Male-Male Displacements There were eight instances of one male displacing another, six were displacements from feeding sites and two were displacements from grooming a female. The two displacements that occurred because of grooming a female were between WY and RY, two likely natal young adult males in the troop. All other displacements involved the alpha male, two were of the young adult males, and three were with immigrant adult males. It is important to note that as data were collected ad lib, and displacements can be subtle, this is likely an underestimate. As all males were seen regularly and in the forefront of the group, however, it is unlikely to be biased. Male Cooperation in Intergroup Encounters Troop A participated in 69 aggressive intergroup encounters. The alpha male was supported by other individuals in the troop in 26 of these. In four IGEs, a subordinate male was identified as participating in the IGE. In one instance, JS and presumptive natal

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16 males RY and WY chased three other males from another troop. JS was seen to chase outgroup males on another occasion with an unidentified male, JS and BL and other troop member chased an unknown troop on an additional occasion. Once, presumptive natal males MY and RY were observed threatening a lone adult male from a different troop. JS did not participate in this encounter. Male Cooperation in Predator Defense We observed two instances of male cooperation in predator defense. One towards an unknown snake and one towards a tayra (Eira barbara). In both instances, LX, the older immigrant male joined JS in mobbing a possible predator. Two other instances of male cooperation in predator defense were observed in a secondary study troop, Troop E. In this troop ER, the alpha male, was observed mobbing a harpy eagle along with CN, an immigrant male. In another case CN and LX, the same older male observed with the main study troop on numerous occasions, mobbed a harpy eagle. ER did not participate in this predator defense. Alpha Male Tolerance of Copulations The alpha male was never seen to harass a subordinate male during a copulation, although he did show aggression to LX when LX was in proximity to a female. 22 copulations were observed in the main study troop. The alpha male was involved in 12 or 55%, the older immigrant male, LX, was involved in four or 18%, and a younger immigrant male, BR, was also involved in four or 18%. The natal male RY was involved in one copulation, and an unknown older juvenile was observed in one copulation.

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CHAPTER 4 DISCUSSION My findings differ from those reported for other populations of brown capuchin monkeys. The male monkeys observed in Suriname exhibit higher rates of grooming, lower rates of aggression, no interference by the alpha male in copulations by subordinate males and assistance by the subordinate males in intergroup aggression (Table 1). Now the challenge is to attempt to explain these differences. What details of the life of male capuchins in Raleighvallen could affect these different social relationships? Table 1: Comparison of Raleighvallen Cebus apella to those at other sites Site Grooming Aggression Copulation Interference Intergroup Aggression Participation Raleighvallen .0063/hr .01/hr No yes Manu (Di Bitetti, 1997) 0 n/a n/a no Iguazu Manu, Peru (Janson 1984, 1985a,b) n/a >.05*/hr Yes (.007/hr) no *aggression by dominant male, the individual responsible for most aggression Group Size and Composition Males living in a large troop with more females are expected to be more affiliative as the sex ratio will be skewed such that one male cannot monopolize all the females (van Hooff, 2000). The study troop in Suriname is on the large range of described brown capuchin troops, consisting of 20-35 animals (3-4 males and 10-14 females). Most brown capuchin groups range from 10-35 animals. Janson (1985) reports group sizes of brown capuchins between eight and fourteen in Manu and Hirsch (2002) reports troop sizes of 23-29 in Argentina. The larger group size seen in Raleighvallen may help 17

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18 account for the increased male-male tolerance seen there. Male brown capuchins in both Argentina and Peru may be more able to monopolize females because of their smaller group sizes, therefore they will show more aggression to additional males joining the troop. In Raleighvallen, there are too many females for a male to monopolize anyway, so he may be tolerant to additional males in the group if they assist in defending the troop from outgroup males. Troop Defense in Exchange for Copulations and Grooming When males from other troops are a threat, the dominant male groom subordinate male or allow them access to females in exchange for their assistance in intergroup encounters (Sussman & Garber, 1987; Goldizen, 1989; van Schaik & Horstermann, 1994; Koenig, 1995). Capuchins at Raleighvallen have high rates of interaction with other troops – 69 aggressive intergroup encounters were observed. In the four intergroup encounters during which subordinate males assisted in troop defense, four subordinate males participated. The males who participated in intergroup encounters were RY, WY, BL and MY. All are natal males except for BL. RY, WY and MY may have been defending the troop because the encounter did not relate to reproduction, but to food. Many encounters occur near a large patch of bamboo, which we suspect is an important food resource. BL and RY were groomed by JS, possibly as payment for assistance in troop defense. If grooming is a necessary payment for assistance in troop defense then it is unclear why WY and MY would also join in unless as suggested above, intergroup encounters were actually over food resources, which they would benefit from, as opposed to females. Besides the alpha male, JS, the males observed copulating were LX, BR, RY and a juvenile male. LX was only observed in the troop for 137 hours yet accounted

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19 for 18% of the copulations observed during the entire study. LX and JS did not show any affiliative behaviors, but did have aggressive interactions. It is possible that JS was so aggressive to LX because of his attractiveness to the females and in this case was demonstrating the tactic of an alpha male who wants to monopolize the females in the group. The other immigrant male who copulated was BR who was observed for 1307 hours and received 18% of the copulations. JS was never seen interacting aggressively or affiliatively with BR and BR did not participate in any intergroup encounters. It seems BR was not allowed these copulations because of any trade offs he had made with JS. Possibly there was something about BR that caused JS to not mind his participation in copulations such as his attractiveness to the females, or maybe BR was such a threat that JS did not want to risk aggression towards him. The third immigrant male, BL, was observed for 1927 hours and was never seen to copulate although he was observed grooming with JS and participated in intergroup encounters. These differences in the tactics of two similarly aged immigrant males, BL and BR, demonstrate the importance of individual strategies to male-male social behavior. Philopatry Generally, affiliation between males is seen in primates where males remain in their natal group (Cords, 2000; van Hooff, 2000). These males may work together to increase their inclusive fitness. In the monkeys at Raleighvallen, the dyads of JS and MY and JS and BL were the ones that groomed the most. MY is very likely a natal male while BL immigrated into the group as an adult. While at first glance affiliation rates in the Suriname capuchins may appear surprising because males are not philopatric, it is possible that the affiliation that occurs is actually between related individuals. Males who

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20 are very likely natal such as MY and RY were also two of the individuals who contributed most to the total rate of male-male grooming. The fact that male monkeys immigrate in this species may be leading us to discount the importance of relatedness to their relationships. Although both MY and RY later left the group, as adults and subadults still within the troop they participated in a large share of the male-male grooming. This also leads to the point that describing monkey troops as single male or multi-male may not be nuanced enough. Eisenberg et al. (1972) mentions the importance of the age graded multi-male troop. Age graded troops consist of multiple males, but of different ages. These troops may show more affiliation than strict multi-male troops, as the males are of different ages and may not be as competitive with each other as they may not be competing for similar resources. There is evidence that younger males, as they are still growing, cannot afford to participate in social behaviors that may take away from foraging time as much as older males (Matsubara, 2003). Further Comparisons The results above give us some insights into the variability of the character of male-male relationships when compared through an intraspecific perspective. If we move to higher level of comparison between different primate species, the variability becomes even more evident (Table 2). Although the different methodologies used in the various studies and the different ways the data are presented make it difficult to compare all the studies across the board, we can look at the results presented in 25 different studies of primate social behavior and attempt to draw some conclusions.

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Table 2: Comparison of male-male relationships across species Site Species Groom Aggression Displacements Participation in IGE Grp size # hours Male Philopatric? RV C.apella .0063 .01 .0038 Yes 20-35 3600 N Iguazu , Argentina (Di Bitetti, 1997; Hirsch, 2002) C.apella 0 No 23-29 740 N Manu, Peru (Janson 1984, 1985ab) C. apella >.05* No 8-14 3000 N La Macarena, Colombia (Izawa, 1980) C. apella .07 8 1.79 .07 8 16 110 8 3.89 N Santa Rosa, Costa Rica (Jack, 2003) C. capucinus 10 s/h not incidents Rare 1198.25 N Lomas Barbudal, Costa Rica (Perry, 1996; Perry, 1998) C. capucinus .3 s/hr 6 .2 s/hr7 .04 6 .147 Yes 21 364.5 N Barro Colorado Island, Panama (Wang & Milton, 2003) Alouatta palliata .018 .018 227.35 ? Costa Rica (Zucker & Clarke, 1986) Alouatta palliata .2 4 23 122 ? Venezuela (Neville, 1972) Alouatta seniculus 60 sec. 5 603 ? Hato Masaguaral, Venezuela (Sekulic, 1983) Alouatta seniculus .03/male/hr Unknown ? Brazil (Strier, 1992; Strier et al., 2002) Brachyteles arachnoids .11.1 1 .0008 .006 1200 Y Yakushima Island, Japan (Nakagawa, 1998; Takahashi & Furuichi, 1998; Matsubara, 2003) Macaca fuscata high >1.4* Yes large Unknown N Affenberg Salem, Germany (Preuschoft et al., 1998) Macaca sylvanus 2 Less than other age/sex classes; 10% of trials 600trials N Captivity (Matheson & Bernstein, 2000) Macaca mulataa .077 220 N Somanathapur Troop (Simonds, 1974) Macaca radiata Yes 15months N Moray River troop (Simonds, 1974) Macaca radiata No 15months N 21

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Table 2 Continued 22 Africa (Kummer, 1968) Paio hamadryas Less than chance 835 Y (Eaton, 1984) Papio anubis .375/hr 179.96 N Amboseli, Kenya (Hausfater, 1975) Papio cynecephalus 4.9/hr 222.1 N Kibale, Uganda (Struhsaker, 1977) Ceraopithecus ascanius scmidti .036 552.8 N Kibale, Uganda (Firos, 2001) Colobus badius tephrosceles .22 .33 Yes 41 36.3 Y India (Hrdy, 1974) Presbytis entellus .38 yes 156 N Madagascar (Sussman et al., 2003) Lemur catta 1% of activity/day 3 40 N Ngogo, Kibale, Uganda (Watts, 2000) Pan troglodytes 88%-91% of all grooming 1500 Y # of incidents per hour Groom= rates of male-male grooming. Aggression= rates of male-male aggression. Includes threats, lunges, chases, biting, possibly displacements. May be unidirectional from one animal to other with no response, or may include response from 2 nd individual. Displacements= rates of male-male displacement. One animal moves away from food resource or grooming partner immediately upon the approach of another. * aggression by dominant male, the individual responsible for most aggression 1 species does not groom – “embraces” instead (Strier et al 2002, Strier 1992) 2 Semi-free ranging, results presented are from experimental tests 3 less than other age/sex classes 4 Mostly “supplantations” 5 Only adult malesubadult male. No adult maleadult male observed 6 before a male rank reversal occurred 7 after male rank reversal occurred 8 Group M 9 Group E

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23 Male-male grooming rates range from zero to 1.7/hr and 88-91% of all grooming while aggressive incidents range from .01/hr to 4.9/hr. Species with male philopatry are expected to exhibit higher rates of affiliative behaviors like grooming (van Schaik & van Hooff, 1983), and indeed relatively high rates of male-male grooming were found in Colobus badius (Firos, 2001)but Macaca fuscata and Cebus apella in Colombia also exhibit high rates, and neither of those species is described as male philopatric (Izawa, 1980; Takahashi & Furuichi, 1998). Other patterns are also hard to discern. Many of the species in which subordinate males assist in intergroup encounters do also exhibit male-male grooming but there is only one study in which it was stated that males did not participate in IGEs and this fact is unknown for many studies in the table. Also, as discussed above, grooming may not always be traded for assistance in group defense. The effect of group size is also hard to see from this comparison. Four species with groups of 20 or more (C. apella in RV, C. capucinus, Macaca fuscata and Colobus badius) have reported instances of subordinate males assisting in IGEs. Again, not all studies report these data, and C. apella in Iguazu have large group sizes but no participation in IGEs. The lack of clear patterns among these studies, and the fact that the brown capuchins in Suriname have surprising rates of affiliation when considered as a female philopatric species, but that when studied on an individual level the bulk of the affiliation is between related individuals, demonstrates the importance of looking at these social behaviors at the individual level. It is accepted that social behaviors are the result of individual strategies (van Schaik & van Hooff, 1983) and that these strategies are not necessarily discrete, but exist on a continuum (Janson, 1988). Despite this,

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24 primatologists often present descriptions of social behavior aggregated to the species level. This obscures much of the variation that really occurs, and as in this study, may even misrepresent the actual data. A brief perusal of this table indicates the need for more basic data on the character of male-male relationships. Many of these studies do not report all the results useful to exploring male-male relationships. Lately, descriptive data seems to have fallen out of favor in primatology (Fedigan, 1992) but as our appreciation of the complexity and number of variables affecting primate social behavior increases, it becomes even more imperative that we collect data on a number of populations within the same species. Brown capuchins, for example, have been most thoroughly studied at only two other sites – Manu, Peru and Iguazu, Argentina (Janson, 1984; Janson, 1985a; Janson, 1990; Janson, 1996; Di Bitetti, 1997; Di Bitetti & Janson, 2001; Hirsch, 2002). Three populations of capuchin monkeys is not a large data set for comparing factors that affect male-male behaviors. Another issue is that the average number of hours of duration of the studies listed here (when available) is 745.6 hours with a high of 3600 hours (this study) and a low of 3.8 hours (Izawa, 1980). If a researcher observed monkeys for eight hours a day, it would only take 93 days to complete a 745 hour study. This is not sufficient time to truly investigate the decisions male monkeys must make on a day-to-day basis. This study, along with other research, has shown that the individuality of males in addition to their life history situations, have an important effect on their behavioral decisions. Short term studies cannot hope to capture the details that are needed to truly discover which variables are most important to predicting aspects of male-male behavior.

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25 Primates have relatively long lives and interact with other individuals on a daily basis. They have opportunities to learn from these interactions and adjust their strategies. Even when male strategies are studied within one troop, variability can be seen between members of the troop who would be expected to make similar decisions based on age and position in the troop. Hausfater (1975) describes life history as relating population biology to the study of individual behavior. I think this study indicates the importance of life history variables in male-male behavior and the need for more long-term studies of populations of primates of all species.

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BIOGRAPHICAL SKETCH Laurie Kauffman was born in Orange, California, but spent most of her formative years in St. Louis, Missouri, where she attended Rosati-Kain High School. Laurie attended Grinnell College where she majored in anthropology. While at Grinnell, Laurie completed a semester abroad in Costa Rica where she studied the impact of tourists on white-faced capuchins and volunteered at a wildlife rehabilitation center. After graduation Laurie worked as a field assistant for Sue Boinski for a year in Suriname. She entered graduate school at the University of Florida in 2002. 33