Intergroup Encounters Research Articles

Intergroup Encounters of Chimpanzees (Pan troglodytes) from the Female Perspective

Intergroup Encounters of Chimpanzees (Pan troglodytes) from the Female Perspective

The effects of recalling positive and negative contacts on linguistic discrimination towards migrant people

The present research aims to test whether varying the sequential position in which majority members recall positive and negative contacts with migrants affects the linguistic descriptions of these episodes - in terms of abstraction and valence - provided by majority group members. We also tested whether participants' prior contact with migrants and distance in time of the recalled contact experiences moderated the effect of the recall on linguistic discrimination. Across two experimental studies, evidence consistently showed that participants who recalled first positive and then negative interactions expressed less linguistic discrimination against migrants in the second event recalled, compared to those who recalled two negative interactions. Moreover, participants who reported having fewer positive intergroup experiences expressed less linguistic discrimination against migrants in recalling negative and then positive interactions, compared to recalling two positive interactions. Findings of Study 2 also revealed an effect of the temporal distance of the recalled events, with more beneficial effects of positive-negative sequences of contact when participants retrieved temporally recent compared to distant intergroup encounters. Overall, this research highlights the key role of positive contact in counteracting the effects of negative contact, leading to a reduction in linguistic discrimination.

Intra- and Intergroup Spatial Dynamics of a Pair-Living Singing Primate, Indri indri: A Multiannual Study of Three Indri Groups in Maromizaha Forest, Madagascar

Territorial pair-living species tend to occupy and defend stable areas, assumed to contain all the resources needed for the lifetime of the group. Furthermore, groups have to mediate spatial relationships with neighboring groups. We investigated the relationship between social and spatial dynamics at the intra- and intergroup level in a pair-living territorial singing primate: the indri (Indri indri). We collected spatial data on three neighboring groups during 396 sampling days between 2009 and 2014 in Maromizaha forest, Madagascar. We evaluated the stability of territories in terms of size and location using minimum convex polygons, defined the presence and stability of core areas, and investigated if singing locations and intergroup encounters were concentrated in the core areas. Territories were generally stable in location and size, although some degree of territorial shift occurred, leading to readjustment of intergroup spacing. Groups had core areas that were not stable across years but were concentrated in the area of the territories that groups occupy consistently over time (stable areas). Singing locations were equally distributed inside and outside core areas, suggesting an even distribution through the territories; meanwhile 9 of 12 intergroup encounters took place in the core areas at the edge of territories. Together, our results support the pattern of territorial stability predicted for a pair-living species, where groups regulate territory exclusivity and spacing with neighbors. Singing behavior also plays an important role in mediating intergroup spatial dynamics. The spatial pattern we found in indris is comparable with that found in other territorial and pair-living primates with different ecological needs, suggesting that in addition to ecological factors, social dynamics influence intergroup spatial dynamics.

Do Monkeys Avoid Areas of Home Range Overlap Because They Are Dangerous? A Test of the Risk Hypothesis in White-Faced Capuchin Monkeys (Cebus capucinus)

In social animals, areas where the home ranges of neighboring groups overlap are often underused. The Risk Hypothesis posits that the costs of intergroup conflict create a “landscape of fear,” discouraging the use of such shared areas. To test this hypothesis, we observed the behavior of white-faced capuchins (Cebus capucinus) in central vs. peripheral areas of their home ranges. If capuchins perceive areas of home range overlap as “risky,” we predicted they would change activity budgets, vocalization rates, and foraging behavior in these areas. A spatially explicit behavioral comparison based on nearly 100 h of focal follows revealed that capuchins socialize less in the periphery (vs. the center) of their home range. Time spent resting, foraging, and engaging in vigilance, as well as vocalization rates, varied in consistent ways across all four study groups, but these differences did not reach statistical significance. Fruit trees near range borders (vs. the center) contained more ripe fruit, and groups spent more time in these trees, with more individuals entering to feed and consuming more fruits. However, capuchins did not alter their foraging behavior in potentially risky peripheral areas in a manner consistent with predictions of optimal foraging theory: intake rates at patch departure were not significantly lower and groups depleted trees to a greater extent along the periphery vs. in the center of their range. These results suggest that while peripheral areas are perceived as risky and this “landscape of fear” contributes to behavioral changes, they also provide resources whose value may outweigh the cost of intergroup encounters.

Against all odds: Numerical assessment by tufted capuchin monkeys

When competitors are able to assess the asymmetry in the resource holding potential before interacting, individuals or groups should avoid interacting with stronger opponents, thereby avoiding the energy costs and risk of injury associated with aggressive intergroup encounters. Thus, escalated aggression is expected only between closely matched competitors. Among Argentine tufted capuchin monkeys (Sapajus nigritus), intergroup dominance is decided by the asymmetry in male group size. Using playback experiments, I simulated intergroup encounters with neighboring groups, manipulating both the apparent numerical asymmetry and the resource context. During experimental trials, I recorded the approach behavior of the focal individual, as well as changes in neighbor density and individual travel speed following the presentation of the playback stimulus, to assess whether individual willingness to participate in resource defense was affected by the probability of winning the encounter. In spite of the competitive disadvantage, neither males nor females showed a decreased probability of approach when the numerical odds strongly favored the opposing group. Instead decisions regarding whether to participate appear to be driven primarily by the resource context. Nevertheless, changes in individual behavior during approaches suggest that tufted capuchin monkeys are sensitive to the relative odds. Individuals accelerated less when approaching a larger group, although no changes in neighbor density were apparent. The absence of an effect of the numerical asymmetry on willingness to approach the playback speaker suggests that subordinate groups benefit from engaging in intergroup aggression with larger neighbors, despite the high probability of losing. These encounters may serve to assess the current subjective resource valuation of the neighboring group or limit territorial expansion by large groups by decreasing the marginal value of home range exclusivity. Because these encounters are riskier, however, individuals appear to alter their approaches, becoming more tentative as the numerical odds increasingly favor the opposing group.

Contact Logger: Measuring everyday intergroup contact experiences in near-time

Intergroup contact research has traditionally relied on retrospective accounts of intergroup encounters, mainly through survey-based or observational methods. This study introduces and tests the usability of a purpose-built, location-aware mobile application—the Contact Logger. This application enables the recording of interpersonal and intergroup encounters, in public and private spaces (both indoor and outdoor), in their here-and-now contexts. The main advantage of this approach, as compared to traditional methods, lies in its ability to collect repeated and timely (near-time) self-assessments of individuals’ behaviors and experiences. It also allows for geographical location data to be logged. Usability testing was conducted in a real-world environment and took place over the course of seven days, during which participants (N = 12) logged every contact they had with an outgroup member (here, older people). Subsequently, participants completed a paper-and-pencil questionnaire, reporting on the usability and experience of using the Contact Logger. The results showed that the application is a viable and easy-to-use alternative to traditional methods. The information gathered aided the further development and optimization of the application. The outcomes of this development process are also briefly discussed.

Impacts of Intergroup Interactions on Intragroup Behavioral Changes in Javan Gibbons (Hylobates moloch)

Agonistic intergroup interactions can cause individual costs such as physical injuries, increased physiological stress, and disrupted intragroup social relationships. Therefore, individuals should employ behavioral strategies to minimize the cost associated with aggressive intergroup encounters (IGEs). We investigated the behavioral strategies of territorial, pair-living Javan gibbons (Hylobates moloch) in response to intergroup aggression, including 1) changes in activity budgets, 2) affiliative behaviors within pairs, and 3) potential intergroup avoidance strategies, such as sleeping tree selection. We observed 129 encounters in three habituated gibbon groups surrounded by four unhabituated groups in Gunung Halimun-Salak National Park, Java, from 2014 to 2016. Overall, gibbons significantly altered their activity budgets during IGEs: they foraged less and were less active than when there was no encounter. We also found a decrease in grooming within pairs following IGEs compared to a matched-control period. However, we did not find any effects of the intensity of aggression, outcome, length of, or female participation in IGEs on grooming within pairs in the hour after an encounter. Male gibbons slept farther away from the IGE location after aggressive IGEs than after neutral encounters. Our results suggest that not only primates living in large groups but also primates living in small groups, such as Javan gibbons, may develop behavioral strategies to deal with direct (during encounters), immediate (within 1 h after encounters), and possibly longer (at the end of a day with encounters) effects of intergroup interactions.

Comparisons of between-group differentiation in male kinship between bonobos and chimpanzees

Patterns of kinship among individuals in different groups have been rarely examined in animals. Two closest living relatives of humans, bonobos and chimpanzees share many characteristics of social systems including male philopatry, whereas one major difference between the two species is the nature of intergroup relationship. Intergroup relationship is basically antagonistic and males sometimes kill individuals of other groups in chimpanzees, whereas it is much more moderate in bonobos and copulations between individuals of different groups are often observed during intergroup encounters. Such behavioural differences may facilitate more frequent between-group male gene flow and greater between-group differentiation in male kinship in bonobos than in chimpanzees. Here we compared differences between average relatedness among males within groups and that among males of neighbouring groups, and between-group male genetic distance between bonobos and chimpanzees. Contrary to expectation, the differences between average relatedness among males within groups and that among males of neighbouring groups were significantly greater in bonobos than in chimpanzees. There were no significant differences in autosomal and Y-chromosomal between-group male genetic distance between the two species. Our results showed that intergroup male kinship is similarly or more differentiated in bonobos than in chimpanzees.

Beyond the group: how food, mates, and group size influence intergroup encounters in wild bonobos

AbstractIn social-living animals, interactions between groups are frequently agonistic, but they can also be tolerant and even cooperative. Intergroup tolerance and cooperation are regarded as a crucial step in the formation of highly structured multilevel societies. Behavioral ecological theory suggests that intergroup tolerance and cooperation can emerge either when the costs of hostility outweigh the benefits of exclusive resource access or when both groups gain fitness benefits through their interactions. However, the factors promoting intergroup tolerance are still unclear due to the paucity of data on intergroup interactions in tolerant species. Here, we examine how social and ecological factors affect the onset and termination of intercommunity encounters in two neighboring communities of wild bonobos, a species exhibiting flexible patterns of intergroup interactions, at Kokolopori Bonobo Reserve, Democratic Republic of the Congo. We recorded the timing and location of intercommunity encounters and measured fruit abundance and distribution, groups’ social characteristics, and space-use dynamics over a 19-month period. We found that intercommunity tolerance was facilitated by a decrease in feeding competition, with high fruit abundance increasing the likelihood of communities to encounter, and high clumpiness of fruit patches increasing the probability to terminate encounters likely due to increased contest. In addition, the possibility for extra-community mating, as well as the potential benefits of more efficient foraging in less familiar areas, reduced the probability that the communities terminated encounters. By investigating the factors involved in shaping relationships across groups, this study contributes to our understanding of how animal sociality can extend beyond the group level.

Effect of Group Size and Individual Characteristics on Intergroup Encounters in Primates

Intergroup encounters are common in nonhuman primates and can vary from affiliative to aggressive. We extracted data from the literature to test five different hypotheses: 1) where there are group size differences between opposing groups, whether the larger group is more likely to win an intergroup encounter than the smaller group; 2) whether the likelihood of a group engaging in aggressive intergroup encounters increases with group size; and 3–5) whether dominant, older individuals, and/or males are more likely to participate aggressively in intergroup encounters than subordinate, younger individuals and/or females. Our data set comprised 52 studies on 31 primate species (3 lemur species, 5 New World monkeys, 19 Old World monkeys, and 4 apes). We found that the larger group is more likely to win an encounter against a smaller group than vice versa. We found no significant relationship between group size and propensity to be aggressive during intergroup encounters. We found weak/no support for the effect of age, dominance rank, and sex on the frequency of aggression displayed toward outgroup individuals during intergroup encounters. Species- and population-specific differences in inter- and intragroup competition and in the degree of the unequal distribution of resources across group members may explain why age, dominance rank, and sex are not strong predictors of aggression during intergroup encounters.

Deprovincialization as a key correlate of ideology, prejudice, and intergroup contact

This paper aimed to examine deprovincialization, defined as a less ingroup-centric worldview fostering openness to other cultures and outgroups, and to test its relationships with personality, cognitive styles, values, political ideologies, intergroup contact, and prejudice. In Study 1, we proved the factorial validity of the Cultural Deprovincialization Scale (CDS), an instrument specifically designed to assess a growing acceptance of other peoples and cultures following intergroup encounters, and we provided evidence for its construct validity by exploring its nomological net. People scoring higher on the CDS were more extraverted, agreeable, open to experience, cognitively flexible, and scored lower on social dominance orientation, right-wing authoritarianism, and nationalism. Moreover, deprovincialized people reported higher scores on positive contact, lower scores on negative contact, better outgroup attitudes, and lower levels of prejudice. In Study 2, using a longitudinal design, we tested the within- and between-individual associations that deprovincialization had with positive and negative intergroup contact, outgroup attitudes, and prejudice. Both between-individual and within-individual variations in positive and negative contact predicted time-varying deprovincialization, whereas between-individual and within-individual variations in deprovincialization predicted time-varying outgroup attitudes and prejudice, controlling for age, gender, and social dominance orientation, and also for contact when deprovincialization was a predictor.

Social influences on grooming site preferences in wild bonobos (Pan paniscus) at Wamba, DRC.

Social grooming is assumed to have both social and hygienic functions. In monkey species, body site preferences during social grooming are related to both the dominance ranks of participating individuals and strength of social bonds. It is suggested that low-ranking groomees and individuals with weak social bonds expose less vulnerable sites of their body because doing so allows them to avoid eye contact, thus reducing the risk of aggression. This study aimed to investigate the influence of (1) the levels of affiliation (through analyses of sex, grooming frequency, and group membership during intergroup encounters), (2) dominance, (3) kinship, and (4) age on grooming site preferences (head, front, back, anogenital region, and limbs) in wild bonobos. Subjects were two groups of wild bonobos living in Wamba, DR Congo. Body site preferences were documented from video clips. Our results illustrate that the levels of affiliation between individuals and their dominance status do not seem to influence body site preferences, contrasting with results in monkey species. However, the selection of body sites was mostly influenced by age and kinship. Mothers were found to groom less accessible sites on their immature offspring's body more than when grooming a non-related immature, suggesting that mothers invest in their offspring more to prevent diseases linked to ectoparasites. Finally, mature individuals groomed the inaccessible back more often than immature individuals, while the latter focused their grooming on the head and front. Overall, this study suggests hygienic functions of social grooming in wild bonobos.

What makes a pair bond in a Neotropical primate: female and male contributions.

Pair living and pair bonding are rare in mammals, and the mechanisms of their maintenance remain a puzzle. Titi monkeys, a ‘textbook example’ for ‘monogamous’ primates, have strong pair bonds and extensive male care. To investigate mechanisms of pair-bond maintenance, we studied seven wild groups of red titis (Plecturocebus cupreus) in Peruvian Amazonia over a period of 14 months. We analysed pair bonds by measuring proximity, grooming and approaches/leaves within pairs, and collected data on intergroup encounters. Females contributed to grooming more than males, especially during infant dependency, when most of the grooming within pairs was done by females. Females were also more active in controlling proximity between pair mates, making most of the approaches and leaves. Males, on the other hand, invested more in territorial defences. They participated in more intergroup encounters than females and were more active during these encounters. Our data is most consistent with the ‘male-services’ hypothesis for pair-bond maintenance, where a female contributes more to the proximity and affiliation maintenance while a male provides beneficial services.

The Influence of Loud Calls on Intergroup Spacing Mechanism in Black Howler Monkeys (Alouatta pigra)

Long-distance vocalizations form an integral part of intergroup spacing mechanisms. The decision to approach, retreat, or ignore loud calls of neighboring groups might be influenced by resource availability, location in the home range, presence of fertile females or infants, or differential resource-holding potentials, and can alter intergroup encounter rates. During a 19-mo study (February 2016–August 2017), we examined navigation decisions relative to neighbor’s loud calls for five groups of black howler monkeys (Alouatta pigra) in Palenque National Park, Mexico. Study groups encountered any of their neighbors at a mean rate of one every 3.5 days and the same neighbor at a mean rate of one every 16.7 days, which was significantly more frequent than would be expected based on a simulation model that randomized observed daily paths. These results are consistent with mutual attraction. Based on 368 travel bouts relative to nearby (50–300 m) calls of neighbors, study groups were more likely to approach calls of neighbors than would be expected by chance, but only when neighbors were close by (50–150 m), suggesting that the imminence of threat by opponents played a role. Of the nine social and ecological predictor variables considered, availability of ripe fruits and of flowers was an important driver of their navigation choices and groups were more likely to move toward neighbors’ calls when ripe fruits were scarce and to move away when flowers were abundant. We found no evidence that the presence of fertile females or unweaned infants influenced navigation decisions. Nor did relative competitive abilities of opposing groups, measured as numeric superiority in group size or male group size, affect navigation decisions. This study provides evidence that black howler monkeys incorporate information on resource availability and neighbors’ current locations into their navigation decisions and intergroup spacing patterns.

Intergroup Competition Enhances Chimpanzee (Pan troglodytes verus) In-group Cohesion

In-group cohesion is an essential component of successful intergroup competition in both human and nonhuman animals, likely facilitating group members access to potential benefits. However, when benefits are equally shared among group members, group defense becomes a collective action problem, which might subvert cohesive participation during intergroup competition. There is a lack of consensus across studies and species with regard to the link between in-group cohesion and intergroup competition, likely as a result of species differences in managing the collective action problem. Here, we examine this link in a species with a striking example of collective action during intergroup competition, chimpanzees (Pan troglodytes verus). Using two years of focal-follow data on males and females in two groups at the Taï Forest, Côte d’Ivoire, we investigated the immediate and long-term effects of intergroup competition (border patrols and intergroup encounters) on measures of in-group cohesion, namely modularity, party size, and intergroup aggression. We found that groups’ association patterns were less modular (more cohesive) in months in which they engaged in more border patrols and intergroup encounters. We found that current and greater prior engagement in intergroup competition predicted larger party sizes. Furthermore, current, but not prior engagement in intergroup competition, predicted reduced intragroup aggression by males but not by females. Increased in-group cohesion in chimpanzees likely reduces potential costs of intergroup competition engagement, by facilitating joint participation in current and future intergroup conflicts, overcoming the collective action problem.

Greeting Behaviors in Male Alouatta palliata at La Pacifica, Costa Rica

Greeting behaviors are ritualized, nonaggressive interactions that serve as a form of tactile communication between two individuals; however, our understanding of the function of male greetings and how they vary inter- and intraspecifically is limited, particularly in Neotropical species. I examined greeting behavior in male Alouatta palliata to determine their social function by testing the tension reduction, social bonding, and formal dominance hypotheses. I collected 1751 h of behavioral data on two groups (G2 and G12/42) of similar size and sex ratio, with clear male dominance hierarchies. The overall number of greetings was low in both groups (N = 36 for both groups). More greetings occurred during times of social disruption (i.e., intergroup encounters, competition for food or females) than during neutral contexts (i.e., traveling or resting without potentially cycling females nearby), though frequencies varied by context in each group. Greetings occurred during all intergroup encounters in G2 but not in G12/42. With the exception of the competitive context in G12/42, alpha males and the higher-ranked male in the dyad initiated the majority of greetings in all contexts, though unidirectionality was not consistent. The pattern of greetings differed among dyads and between the groups. Subordinates in the dyad initiated more greetings than dominants only in G12/42 in the context of competitive activities, and the number of greetings decreased in G12/42 as rank distance increased. These results partially support the tension reduction hypothesis, and suggest greetings communicate nonagonistic intent among males. However, the nature of these encounters can vary by dyad and group within the same population, suggesting that greetings may also be partly driven by differing group histories, the social and ecological environments surrounding each group, and individual male temperaments.

Neighbourhood-scale public spaces, inter-group attitudes and migrant integration in Beijing, China

Cities worldwide face the challenge of persistent social polarisation that is exacerbated by the mass migration of populations. Scholars have debated whether the planning of public spaces, which presumably fosters inter-group encounter, potentially reduces prejudice against minorities such as migrants, and eventually promotes social inclusiveness. This research uses a large-scale questionnaire survey conducted in 36 neighbourhoods (estates) in Beijing, China, combined with field observations and interviews, to investigate whether the presence, perception and use of neighbourhood-scale spaces of encounter are relevant in predicting residents’ attitudes towards migrant social inclusion, particularly with respect to equal access to citizenship and government welfare. Qualitative and quantitative analyses found that residents’ inclusiveness attitude is less associated with the physical presence of public spaces and facilities in the neighbourhood, and more with actually using such spaces for neighbourly encounters in daily life. The findings echo recent critiques of the romanticised view of public spaces for urban encounters, and suggest that neighbourhood planning of public spaces should incorporate elements from social projects that facilitate meaningful interaction between native and migrant residents to achieve the goal of building an inclusive city.

Genetic Analysis of Migration Pattern of Female Bonobos (Pan paniscus) Among Three Neighboring Groups

Relationships between females of different groups in female philopatric species are typically antagonistic, whereas those in female dispersing species can be more moderate. Such nonantagonistic relationships among females of neighboring groups may allow immigrant females to minimize dispersal costs by migrating into those groups, whereas the frequency of female migration among neighboring groups is little understood in female dispersing species. Bonobos (Pan paniscus) are a species in which females disperse and often show affinitive interactions between groups during intergroup encounters. We examined the frequency of female migration into neighboring groups in bonobos using genetic and demographic data. We studied 27 immigrant female bonobos in three neighboring groups at Wamba, Democratic Republic of the Congo. We estimated the frequency of female migration into neighboring groups using the following formula: the number of females that migrated into any neighboring group/the number of females that migrated into any nonnatal group. We estimated the number of females that migrated into any neighboring group using genetic evidence for female migration among the three groups, and the number of neighboring groups for the three groups. We estimated the number of females that migrated into any nonnatal group using the age of subject females, age of first birth, interbirth intervals, and mortality. The estimated frequency of female migration into any neighboring group was 60% (4.5/7.48). Our results suggest that female bonobos do not disperse far from their natal groups, which may be because they usually transfer between groups during intergroup encounters.

Habitat Use in a Population of the Northern Muriqui (Brachyteles hypoxanthus)

Habitat loss and fragmentation are known to restrict the movements of primates, including their ability to expand their home ranges. These effects are especially strong at high densities, where home range overlap can result in high rates of agonistic intergroup encounters over range defense. We investigated habitat use and range defense in a population of northern muriquis (Brachyteles hypoxanthus) at the Reserva Particular do Patrimonio Natural – Feliciano Miguel Abdala, in Minas Gerais, Brazil from August 2010 to July 2013. The four groups in this isolated population used 878 ha of forest, with home ranges exhibiting high interannual fidelity in location and low intergroup overlap. Core areas represented 13–29% of the respective home ranges and, except for one group, showed only moderate to low interannual fidelity in successive years. Of 130 intergroup encounters recorded in 2010–2011, significantly more occurred in core areas that overlapped with the range of another group than in areas of home range overlap or areas used exclusively by one group. Daily path lengths of the one group used in assessing range defensibility varied little (1075–1132 m) across years and relative to home range diameter did not meet the criteria for defensibility. However, the occurrence of independent subgroups, combined with a mean monthly detection distance of 242 m, provides strong evidence of range defensibility. These findings point to the importance of fission–fusion dynamics for intergroup range defense, particularly in primates living at high densities in fragmented habitats.

How to Enhance the Effects of Mediated Intergroup Contact? Evidence from Four Countries

We bridge the theorizing on mediated and imagined contact and integrate these two contact forms in one sequence within a single design. We experimentally examine whether (1) encouraging people to imagine a positive intergroup encounter prior to reading a personal story of an outgroup member as well as (2) mediated contact with an outgroup member similar or dissimilar to the ingroup prototype, improve outgroup attitudes. We also test the affective and cognitive mediators through which these effects emerge. Data from four different countries that test attitudes toward four distinct immigrant groups find that although imagined contact and similarity do not consistently improve outgroup attitudes, enhanced interest in the story of an outgroup member and positive emotions mediate the effects from similarity, and – in two countries – from imagined contact. Theoretical and practical implications of the findings are discussed.