Aggressive intergroup encounters in two populations of Japanese macaques (Macaca fuscata)

It is predicted that variation in intergroup relationships in group living primates reflects the cost and benefit of resource defense. We tested the applicability of the model by examining population difference, group difference, and seasonal difference in behaviors during intergroup encounters in two populations of Japanese macaques (Macaca fuscata), one of six groups from Yakushima Island, and the other of three groups from Kinkazan Island. We found that the nature of intergroup encounter varied with group identity, reproductive seasonality, and population. Yakushima groups showed aggressive behaviors more frequently than did Kinkazan groups and the difference was consistent with the food competition model, both because of the involvement of females, and because home ranges were smaller on Yakushima than on Kinkazan, and thus more defensive. Both sexes of animals participated in aggressive interactions, but males were more aggressive than females. Furthermore, Yakushima population showed more agonistic intergroup behaviors during the mating season than the non-mating season. Also during the encounters, intergroup mating was observed, but only in Yakushima. It is concluded that intergroup relationships reflect the mate guarding behavior by group males. However, the agonistic relationship during non-mating season, especially that of among females, is also consistent with the food competition model. It is also noted that males' behavior toward other groups can also be interpreted as a form of investigative behavior before possible transfer into a new group.     

Intergroup interactions in Tibetan macaques at Mt. Emei,China

Data on intergroup-interactions (I-I) were collected in 5 seasonally provisioned groups (A, B, D, D₁, and E) of Tibetan macaques (Macaca Thibetana) at Mt. Emei in three 70-day periods between 1991 April–June (P1), September–November (P2), December–1992 February (P3). The I-I were categorized as forewarning made by high-ranking males (including Branch Shaking and/or Loud Calls), long-distance interactions in space (specified by changes in their foraging movements), and close encounters (with Affinitive Behavior, Male's Herding Female, Sexual Interaction, Severe Conflict, Adult Male-male Conflict, Opportunistic Advance and Retreat, etc. performed by different age-sex classes). From periods P1 to P3, the I-I rate decreased with reduction in population density as a positive correlate of food clumpedness or the number of potential feeders along a pedestrian trail. On the other hand, from the birth season (BS, represented by P1 and P3) to the mating season (MS, represented by P2) the dominance relation between groups, which produced a winner and a loser in the encounters, became obscure; the proportion of close encounters in the I-I increased; the asymmetry (local groups over intruders) of forewarning signals disappeared; the rate of branch shaking decreased; and sometimes intergroup cohesion appeared. Considering that sexual interactions also occurred between the encountering groups, above changes in intergroup behaviors may be explained with a model of the way in which the competition for food (exclusion) and the sexual attractiveness between opposite sexes were in a dynamic equilibrium among the groups, with the former outweighing the latter in the BS, and conversely in the MS. Females made 93% of severe conflicts, which occurred in 18% of close encounters. Groups fissioned in the recent past shared the same home range, and showed the highest hostility to each other by females. In conspicuous contrast with females' great interest in intergroup food/range competition, adult male-male conflicts that were normally without body contact occurred in 66% of close encounters; high-ranking male herding of females, which is typical in baboons, appeared in 83% of close encounters, and showed no changes with season and sexual weight-dimorphism; peripheral juvenile and subadult males were the main performers of the affinitive behaviors, opportunistic advance and retreat, and guarding at the border. In brief, all males appeared to “sit on the fence” at the border, likely holding out hope of gaining the favor of females both within and outside the group. Thus, females and males attempted to maximize reproductive values in different ways, just as expected by Darwin–Trivers' theory of sexual selection. In addition, group fission was observed in the largest and highest-ranking group for two times (both in the MS) when its size increased to a certain level, and the mother group kept their dominant position in size and rank among the groups that might encounter, suggesting that fission takes a way of discarding the “superfluous part” in order to balance the cost of competition for food and mates within a group, and the benefit of cooperation to access the resources for animals in the mother group. Am J Phys Anthropol 104:459–470, 1997. © 1997 Wiley-Liss, Inc.     

Impact of forest fragment size on between-group encounters in lion-tailed macaques

Between-group encounters are an obvious outcome of intergroup competition. Between-group encounters in primates range from avoidance to fatally aggressive. The prevailing hypotheses explain such encounters as mate defense strategy by males and resource defense strategy by females. However, the rate and nature of between-group encounters may also be influenced by habitat and demographic characteristics. We studied the effect of forest fragment size on group encounters in lion-tailed macaques in the Western Ghats of southern India. The encounter rate decreased as the fragment size increased. Group density and home range overlap correlated positively with the encounter rate. The aggressive encounters were more in the relatively medium-sized fragment where the observed frequency of between-group encounters was higher than the expected frequency than in the small fragment and the large forest complex. Together, these results indicate a complex pattern of effects of fragment size on between-group encounters in primates.     

Intergroup encounters in wild moor macaques (<Emphasis Type="Italic">Macaca maurus</Emphasis>)

We studied intergroup encounters among moor macaques at the Karaenta Nature Reserve, South Sulawesi, Indonesia. Group B has been observed on the basis of individual identification since 1988. We analyzed 85 encounters between members of Group B and members of neighboring groups from September 1990 to November 1998. The average frequency of intergroup encounters was 0.035/hour. Neither the presence of females in estrus nor rainfall had an effect on encounter frequency. Behaviors of moor macaques during intergroup encounters differed from those of Japanese macaques. In moor macaques, no intergroup interactions with body contact were observed during encounters, and females never directed aggression toward members of different groups. The present study did not confirm the prediction of the model ofvan Schaik (1989). Extension of the existing models is required to explain the difference in female dominance styles among macaques by socioecological factors.     

Effect of Seasonality on the Behavior of an Insectivorous Primate, Tarsius spectrum

The distribution and quality of food resources is generally recognized as the preeminent factor explaining much interspecific and intraspecific variation in the behavior of nonhuman primates. Primates that live in seasonal environments often show predictable responses to fluctuating resources. In order to compensate for the reduction in resource availability, primates variously switch to alternative, poorer quality food sources, increase the amount of time they spend foraging, or increase their daily path length. Some primate species reduce their group size or maximize the group dispersion. I address whether spectral tarsiers (Tarsius spectrum), which are insectivores, modify their behavior in the same ways as frugivores and folivores in response to seasonal or scarce resources. My results indicate that wild spectral tarsiers modify their activity budget in response to seasonal resources. Specifically, during periods of low resource availability, spectral tarsier males and females spent more time traveling and foraging compared to their activity budget during the wet season. Males and females not only increased the amount of time they spent foraging during times of low resource abundance but also modified their foraging behavior. During the wet season, when resource abundance was high, they consumed Orthoptera and Lepidoptera with greater frequency than during the dry season. During the dry season, when resource abundance was low, spectral tarsiers still ate numerous Orthoptera and Lepidoptera, but they also increased consumption of Coleoptera and Hymenoptera. Spectral tarsiers were also more likely to be involved in territorial disputes during the dry season than during the wet season. Intragroup encounters decreased in frequency in the dry season versus the frequency of encounters during the wet season.     

Variation in Intergroup Encounters in Two Populations of Japanese Macaques

The nature of intergroup encounters differed between two populations of wild Japanese macaques (Macaca fuscata): the Yakushima and Kinkazan populations. In the Yakushima population, intergroup encounters were more likely to result in the displacement of one group, intergroup agonistic interaction was common, and intergroup dominance was usually distinct. When displacement occurred at Yakushima, larger groups tended to dominate smaller ones. Conversely, in the Kinkazan population, intergroup encounters rarely resulted in displacement, intergroup agonistic interaction was rare, and intergroup dominance was usually unclear. Thus, monkeys in Yakushima appear to defend resources actively during encounters, while those in Kinkazan usually did not defend resources. The frequency of encounters was significantly higher in Yakushima than in Kinkazan. The two populations had very different group densities and traveling speeds, both of which directly influence the chance of encounters. Taking these differences into account, we compared the observed frequency with those predicted by the ideal gas model. The observed frequencies in both populations were about one-third of the number expected with the model, which suggests that the differences in encounter frequency were caused by differences in group density and traveling speed. We discuss this intraspecific variation in light of economic defendability in connection to habitat differences and the evolutionary significance of resource defense behavior.     

Female feeding priority in bonobos, Pan paniscus, and the question of female dominance

The question of whether bonobos show feeding priority and female dominance has been proposed and examined, both in the wild and in captive studies, with differing results. The relationship between female dominance and female feeding priority has been best studied in prosimian primates. These studies use established criteria of females consistently evoking submissive behavior from males in dyadic encounters for determining female dominance. Although the relationship is complex, female dominance in prosimians is associated with preferential access to food. Data from studies of wild habituated bonobos in the Lomako Forest, Democratic Republic of the Congo, are examined for evidence of both female feeding priority and female social dominance using similar criteria as used for prosimians. Bonobos showed evidence of female feeding priority in small, but not in large, food patches. Male-male competition for mating opportunities at the start of the food bout was related to some, but not all, differences in time spent feeding between the sexes. Female dominance similar to that seen in prosimians was not observed in these bonobos. Males were consistently dominant in dyadic interactions. Female feeding priority with male dyadic social dominance implies that male deference during feeding cannot be excluded as one explanation of interpretations of female dominance in bonobos. Additionally, dominance of male bonobos by females appears to require the presence of female coalition partners. As in other primates with female feeding priority, bonobo females express this trait where food is economically defendable. Unlike prosimians, however, bonobo female feeding priority may result from male deference and the importance of female coalitions in nondyadic interactions.     

Patterns of range use,range defense,and intergroup spacing in moustached tamarin monkeys (Saguinus mystax)

In this paper we examine patterns of group spacing and habitat utilization in neighboring groups of marked free-ranging moustached tamarin monkeys (Saguinus mystax) inhabiting Padre Isla, a small island in the Amazon Basin of northeastern Peru, and describe the set of behavioral mechanisms used by tamarins to maintain the spatial isolation and social integrity of individual groups. Specifically, we address a series of questions regarding the importance of resource defense, mate defense, and territorial defense in intergroup interactions. From June through November 1990, we recorded 67 intergroup interactions involving members of our two main study groups. These interactions occurred at a rate of .14/observation hour and were of two general types. Vocal battles averaged 18 min in duration and were characterized by a series of high frequency, short syllable, long calls that were exchanged between groups separated by distances of greater than 25 m. Aggressive encounters averaged 26 min in duration and involved visual contact, alarm calls, scent marking, and sequences of chases and retreats. Intergroup confrontations did not cluster around the perimeter of a group's home range, and there was no evidence that moustached tamarins patrolled range borders. Our data indicate that 35% of aggressive encounters occurred in the vicinity of major feeding trees. Priority access to these sites is likely to have an important influence on tamarin foraging success. Mate defense and the exploration of new breeding opportunities also appear to be important functions of intergroup conflicts. Not only did the frequency of aggressive encounters increase during breeding periods, but three-fourths of all observed copulations occurred during or within 30 min of an encounter. Given the high degree of reproductive competition reported among tamarin females and the time and energy group members devote to intergroup aggression, maintaining access to a stable home range and the resources contained within that range appear to be critical functions of moustached tamarin social interactions.     

Social dynamics of intergroup encounters in the capped langur (Presbytis pileata)

Data from a 15–month field study of the capped langur (Presbytis pileata) in moist deciduous forest in Bangladesh show that during intergroup encounters males respond more aggressively to extra-group males and to the resident males of unfamiliar one-male groups than they do toward familiar males. Lone males followed established one-male groups and attempted to interact with group females. During intergroup encounters males responded to the approach of unfamiliar males with significantly more displays than were given to familiar (frequently encountered) males. The frequency of displays given to approaching groups showed a negative correlation with the frequency of encounters with those groups. In 50% of intergroup encounters males pushed and bit their group females if the females strayed from the immediate proximity of the group male. Further observations suggest that males obtain females that have emigrated from established groups or attempt to interact with them in established onemale groups. Males had a tenure from at least 13 months to at least 26 months, and between 1986 and 1988 no male changes were seen. Capped langur males defended females from other males, but females did not defend resources or participate in intergroup encounters. The implications of this sex difference in behavior during encounters is discussed with regard to ecological models of female-bonded primate groups.     

Contest and scramble competition: patterns of female aggression and ranging behavior among primates

The fact that most female primates (and many other mammals)live in groups is paradoxical, given that the presence of otherspresumably increases competition for foods and may, for some,reduce reproductive success. Competition for food resourcesis generally inferred from any of the following observations:(1) female dominance hierarchies within groups; (2) female aggressionbetween groups; (3) increasing home-range size with increasinggroup size; (4) longer day-range length with increasing groupsize; and (5) lower reproductive rates in larger groups. Bothfemale aggression (interference competition) and adjustmentsof ranging behavior to group size (exploitative competition)have been linked in the past to patterns of food distributionand abundance. Using data largely from the literature, thispaper examines the covariance of female aggression and rangingbehavior among 20 species of primates in an attempt to betterexplain the variation in female relationships within and betweengroups of primates. Results show that groups of females areaggressive toward other groups and that home-range size increaseswith increasing group size in most species. In addition, inthose species with strong dominance hierarchies within groups,day-range length increases as a function of group size. However,in those species that do not have strong dominance hierarchieswithin groups, dayrange length does not increase as a functionof group size. The implications of these results are presentedin a model that suggests that intergroup competition is determinedby food abundance, whereas intragroup competition is determinedby food distribution. This model differs from earlier modelsin its explanation of the ecological conditions that influencefemale relationships within and between groups of primates.[Behav Ecol 1991;2:143–155]     

Sociality in Callithrix penicillata: II. Individual Strategies During Intergroup Encounters

In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil. Agonistic interactions occurred at low frequencies during intergroup encounters. The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.     

Ecological determinants of the behavior and social structure of Japanese monkeys: A synthesis

A review is presented of the results of the various studies in this volume and an attempt is made to establish connections among several features of the ecology, behavior, and social structure of Japanese monkeys. Several studies in this volume suggest that intergroup direct feeding competition has been much more severe in Yakushima, in the warm-temperate region, than in Kinkazan, in the cool-temperate region of Japan. This result is consistent with the predictions that moderate abundance and clumped distribution of food incur more severe intergroup direct competition. However, the number of adult females within a group in Yakushima was smaller than that in Kinkazan even though severe intergroup direct competition should favor large groups. This contradiction can be mainly explained by the less severe intergroup indirect competition in Kinkazan than in Yakushima. By contrast, some studies in this volume also indicate that adult male to female ratio within a group has been higher in Yakushima than in Kinkazan. This result can be explained in two ways: the females in Yakushima might have recruited more males to increase the competitive ability of the group under conditions of severe intergroup direct feeding competition; alternatively, it might be profitable that the males in Yakushima defend females cooperatively as group males against the males in other groups at a moderate density of females. Some studies in this volume suggest that grooming frequency was higher in Yakushima than in Kinkazan. The higher grooming frequency in Yakushima might have been partly due to a constant increase in engaging in social behavior from a decrease in feeding time. Another reason might be that there is a stronger effect of grooming on promotion of formation of coalitions among adults under conditions of severe intergroup direct and intragroup direct competition.     

Urinary C-peptide levels in male bonobos (Pan paniscus) are related to party size and rank but not to mate competition

Within- and between-species variation in male mating strategies has been attributed to a multitude of factors including male competitive ability and the distribution of fertile females across space and time. Differences in energy balance across and within males allow for the identification of some of the trade-offs associated with certain social and mating strategies. Bonobos live in groups with a high degree of fission–fusion dynamics, there is co-dominance between the sexes and a linear dominance hierarchy among males. Males compete over access to females, breeding is aseasonal, and females exhibit sexual swellings over extended time periods. In this study we use urinary C-peptide (UCP) levels in male bonobos (Pan paniscus) obtained from 260 urine samples from a wild bonobo community, to quantify male energy balance during mate competition and levels of gregariousness in the species. Although high ranking males are more aggressive, spend more time in proximity to maximally tumescent females, and have higher mating frequencies, we found no indication that mate guarding or mate competition affected male energy balance. Our results showed a positive correlation between monthly mean UCP levels and mean party size. When traveling in large parties, high ranking males had higher UCP levels than those of the low ranking males. These results support the hypothesis that patterns of fission–fusion dynamics in bonobos are either linked to energy availability in the environment or to the energetic costs of foraging. The finding of a rank-bias in UCP levels in larger parties could also reflect an increase in contest competition among males over access to food.     

Female contributions to the peaceful nature of bonobo society

Although chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) are closely related, females of the two species show surprisingly large differences in many behavioral aspects. While female chimpanzees tend to range alone or in small parties during non-estrous periods, female bonobos aggregate even more often than do males. Female chimpanzees do not have frequent social interactions with other females, whereas female bonobos maintain close social associations with one another. Although the ranging patterns of chimpanzee parties are generally led by males, female bonobos often take the initiative in ranging behavior. While female chimpanzees usually do not exhibit estrus during postpartum amenorrhea or pregnancy, female bonobos exhibit a prolonged pseudo-estrus during such non-conceptive periods. Studies of these two species have also shown great differences in agonistic behaviors performed by males. Male chimpanzees frequently fight with other males to compete for estrous females, but male bonobos seldom do so. While there are many records of infanticide by male chimpanzees, there is no confirmed record of such an event among bonobos. Several cases of within-group killing among adult male chimpanzees have been reported, but there is no such record for bonobos. While intergroup conflicts among chimpanzees sometimes involve killing members of the other group, intergroup conflicts among bonobos are considerably more moderate. In some cases, bonobos from two different groups may even range together for several days while engaging in various peaceful interactions. I will address two important questions that arise from these comparisons, exploring why females of such closely related species show such clear differences in behavior and whether or not the behavioral characteristics of female bonobos contribute to the peaceful nature of bonobo society.     

Intragroup cohesion and intergroup hostility: the relation between grooming distributions and intergroup competition among female primates

In some primate species, females interact affinitively withmany related and unrelated females, whereas in other speciesfemales interact with only a small subset of available partners.One explanation for high rates of affinitive interactions amongfemale members of the same group is that they function to maintainthe group's cohesion in competition for resources against othergroups. Here, I attempt to determine if grooming is more "egalitarian"or diverse in groups that compete aggressively with their neighborsthan in groups in which females rarely take an active role inbetween-group competition. Three types of data are considered.The first concerns grooming and intergroup encounters in onepopulation of free-ranging vervet monkeys. The second concernsgrooming interactions in a captive population of vervets beforeand after females in adjacent cages began to respond aggressivelyto one another. The third involves a literature survey of avariety of species. When only female-bonded species are considered,there is no relation between the diversity of grooming withingroups and female participationin intergroup encounters. Therealso appears to be no clear relation between the strength ofthe female dominance hierarchy and the diversity of groomingamong females. Female-bonded groups are apparently composedof subgroups allied in a loose confederation against other groups.Female members of the same group may compete against other groupsas a cohesive unit, but their grooming relationships are oftensharply differentiated.     

Demography, range use, and behavior in black lemurs (Eulemur macaco macaco) at Ampasikely, northwest Madagascar

We studied a black lemur population over a 2-year period (1992-1993) and 8 years later (2000) in a 50-ha secondary forest in northwest Madagascar. All of the animals were marked to investigate population dynamics and seasonal variation in ranging and behavior, and new data on black lemurs were obtained. Our data on demographic characteristics were expanded to include other forest sites and contrasted with those collected in other Eulemur macaco macaco field studies, in relation to human activity and the presence of introduced and cultivated plant species. Density is affected by deforestation and hunting. Group size and home range depend on the composition of the forest and probably food patches. Sex ratio at birth varies according to the number of females per group, a result that fits the local resource competition model. Groups are multimale-multifemale, and adult females form the core of the groups. Reproductive parameters indicate sharply defined seasonal breeding, a high female reproductive rate, and birth synchrony. Changes in group composition reveal male and female juvenile dispersal, male transfer between groups at the time of mating, and adult female transfer and group fission when groups exceed a critical size. At mating and birth, intergroup agonistic encounters occurred at home-range boundaries, and larger groups were dominant over smaller groups. Patterns of intragroup interactions suggest that males compete for access to groups of females during the mating season, and that females may compete for food resources during the birth season. Our study also reports female social dominance and lack of sexual weight dimorphism in this species.     

Seasonality and Socioecology: The Importance of Variation in Fruit Abundance to Bonobo Sociality

The assumption that nonseasonal, evergreen, rain forests contain more continuously available food resources than seasonal rain forests is fundamental to comparisons made between the socioecology of the male-bonded Pan troglodytes and the female-based social system of the Pan paniscus. Chimpanzee females may be less social due to the high costs of feeding competition, whereas in the more food-rich central African rain forests such as the Lomako forest, female bonobos can associate and socially bond. The Lomako Forest experiences two wet and two dry seasons a year. Data on fruit abundance and sociality show that despite monthly variation in fruit availability, there was no consistent seasonal variation in fruit abundance or dietary breadth. Bonobo use of nonfig fruits, figs, THV, and leaves did not follow seasonal patterns. Leaves and THV may act as complementary sources of plant protein and their use was inversely correlated. Monthly variation in fruit abundance was associated with a significant decrease in the number of males in a party but not in the number of females. Focal males were frequently solitary during 1 of the 3 months with the smallest party sizes. In contrast, females remained social with each other throughout the year. Therefore, seaonality at Lomako appeared to be less marked than at comparable chimpanzee sites, such that the variation in fruit abundance did not fall below a level that prohibits female sociality.     

Factors underlying party size differences between chimpanzees and bonobos: a review and hypotheses for future study

Differences in party size and cohesiveness among females have been primary topics in socio-ecological comparisons of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). This paper aims to review previous studies that attempted to explain these differences and propose some hypotheses to be tested in future studies. Comparisons of recent data show that relative party size (expressed as a percentage of total group size) is significantly larger for bonobos than chimpanzees. Although the prolonged estrus of females, close association between mother and adult sons, female social relationships including unique homosexual behavior, and high female social status might be related to the increased party size and female cohesiveness of bonobos, these social and behavioral factors alone do not appear to explain the differences between the two species. Differences in ecological factors, including fruit-patch size, density of terrestrial herbs, and the availability of scattered foods that animals forage as they travel between large fruit patches could also contribute to the differences between chimpanzees and bonobos. However, these factors cannot fully account for the increased party size and female cohesiveness of bonobos. The higher female cohesiveness in bonobos may be explained by socio-ecological systems that reduce the cost in feeding efficiency incurred by attending mixed-sex parties. These systems may include female initiatives for party ranging movements as well as the factors mentioned above. Because of their geographical isolation, the two species probably evolved different social systems. Chimpanzees, whose habitats became very dry during some periods in the Pleistocene, likely evolved more flexible fission–fusion social systems to cope with seasonal and annual variation in food availability. On the other hand, bonobos had a large refugia forest in the middle of their range even during the driest periods in the Pleistocene. Therefore bonobos, whose habitats had more abundant food and smaller variation in food availability, probably evolved systems that help females stay in mixed parties without incurring large costs from contest and scramble competition.     

Group encounters and territoriality in wild Alaotran gentle lemurs (Hapalemur griseus alaotrensis)

During a 3 month field study, 18 group encounters between four groups of Alaotran gentle lemurs (Hapalemur griseus alaotrensis) were observed in the Lake Alaotra marshland in Madagascar. Behaviors observed during group encounters are described, and quantitative data on intergroup interactions and ranging patterns are discussed in the context of territoriality. Intergroup interactions varied in their intensity, ranging from visual monitoring, scent marking, and display locomotion to penetrating the neighboring range. A quarter (27%) of the encounters were aggressive, involving chases and confrontation displays, and no affiliative interactions were observed. Both adult males and females were involved in intergroup encounters, with males playing more active roles. All encounters took place in the small overlapping areas of neighboring home ranges. The outcome of an aggressive encounter was determined by its location, with the resident group always driving out the intruding one. The Alaotran gentle lemur actively advertised and consistently defended a large area of its home range against intrusion of neighboring groups and can therefore be considered territorial. Am. J. Primatol. 46:251–258, 1998. © 1998 Wiley-Liss, Inc.