Adolescent male chimpanzees (Pan troglodytes) form social bonds with their brothers and others during the transition to adulthood

Social relationships play an important role in animal behavior. Bonds with kin provide indirect fitness benefits, and those with nonkin may furnish direct benefits. Adult male chimpanzees (Pan troglodytes) exhibit social bonds with maternal brothers as well as unrelated adult males, facilitating cooperative behavior, but it is unclear when these bonds develop. Prior studies suggest that social bonds emerge during adolescence. Alternatively, bonds may develop during adulthood when male chimpanzees can gain fitness benefits through alliances used to compete for dominance status. To investigate these possibilities and to determine who formed bonds, we studied the social relationships of adolescent and young adult male chimpanzees (N = 18) at Ngogo in Kibale National Park, Uganda. Adolescent male chimpanzees displayed social bonds with other males, and they did so as often as did young adult males. Adolescent and young adult males frequently joined subgroups with old males. They spent time in proximity to and grooming with old males, although they also did so with their age peers. Controlling for age and age difference, males formed strong association and proximity relationships with their maternal brothers and grooming relationships with their fathers. Grooming bonds between chimpanzee fathers and their adolescent and young adult sons have not been documented before and are unexpected because female chimpanzees mate with multiple males. How fathers recognize their sons and vice versa remains unclear but may be due to familiarity created by relationships earlier in development.     

成年雌性短尾猴的社会联系强度及影响因素

灵长类动物社会中,个体间的社会关系是维系群体稳定的重要基础,也影响个体的寿命和繁殖成功。本研究以栖息于安徽黄山的短尾猴YA1群为对象,采用焦点动物取样法和行为取样法采集成年雌性个体在交配期（2015.9 - 2015.12）和非交配期（2016.3 - 2016.5）的社会行为,通过理毛和近距行为计算社会联系强度,探讨群体成员之间的社会关系及影响因素。结果表明：在交配期和非交配期,雌性短尾猴的社会联系强度无显著差异（t = 0.181,P = 0.857）;亲缘关系和社会联系强度呈显著正相关（交配期：r = 0.534, P = 0.001; 非交配期：r = 0.469, P= 0.001）;个体间的等级距离和社会联系强度呈显著负相关（交配期：r = -0.288, P= 0.014; 非交配期：r = -0.238, P= 0.048）;年龄差异和社会联系强度无显著相关性（交配期：r = -0.176, P = 0.181; 非交配期：r = -0.192, P = 0.151）。本研究提示成年雌性短尾猴个体间会形成稳定的社会关系,亲缘关系和等级顺位是影响个体之间社会关系的重要因素。     

Singing by male and female Kloss gibbons (Hylobates klossii) in the Peleonan Forest, Siberut Island, Indonesia

Kloss gibbons (Hylobates klossii) are endemic to the Mentawai Islands in Indonesia and are one of only two gibbon species in which mated pairs do not sing duets. This is the first long-term study of the factors influencing the singing activity of Kloss gibbons within a northern Siberut Island population and follows two previous studies in central Siberut nearly 30 years ago. We collected data on the presence/absence of male and female singing within the study area on 198 days and within a focal group on 47 days. Rainfall during the time period in which they normally sing inhibits singing in both males and females. Our study supports the hypothesis that male and female songs function in intrasexual resource defence, as singing is associated with singing by same-sex neighbours, and same-sex choruses are more likely to occur after one or more days of silence (from that sex), suggesting there is pressure for individuals to communicate with same-sex neighbours regularly. Singing was not coordinated within a mated pair, suggesting that vocal coordination of the pair has been lost with the loss of the duet and that Kloss gibbon songs do not convey information to neighbours about the strength of the pair bond. On days when males sang predawn, females were more likely to sing after dawn and earlier in the morning. Additionally, the number of groups singing in female choruses was positively associated with the number of males that had sung in the predawn male chorus. We suggest that female songs have an intersexual territory defence as well as an intrasexual function.     

The relationship between duet songs and pair bonds in siamangs, Hylobates syndactylus

One of the most commonly cited functional explanations for animal duet songs is strengthening of the pair bond. However, the evidence to support this view is, at best, limited. This study provides support by documenting a relationship between pair bonds and duet singing in siamangs. As a working hypothesis, we assume that if duetting were related to pair bonding, we might expect to see a relationship between duetting intensity and indicators of pair bond strength. Like most gibbon species, siamang pairs produce loud, long and well-coordinated duet songs. We recorded daily frequency and duration of duetting and three generally accepted indicators of pair bond strength (mutual grooming, behavioural synchronization and distance between mates) in 10 siamang groups in zoos. Duetting activity was positively correlated with grooming activity and behavioural synchronization, and negatively correlated with distance between mates. These results suggest that the production of coordinated duets by siamang pairs is related to pair bonding. Copyright 2000 The Association for the Study of Animal Behaviour.     

Sound Spectrum Characteristics of Songs of Hainan Gibbon (Nomascus hainanus)

Gibbons are characterized by their species-specific calls, or songs. There are few studies of songs of Hainan gibbon (Nomascus hainanus). To study the sound spectrum characteristics and test for intergroup differences in Hainan gibbon song, we studied the singing behavior of Hainan gibbons in Bawangling National Nature Reserve, Hainan Province, China, intermittently from August 2002 to February 2013, collecting 184 recordings. Our results show that: 1) Hainan gibbon song bouts occur mainly 0–4 h after dawn. 2) The songs of adult males living in groups are composed mainly of one to three short notes and one to five long notes, while solitary adult male songs consist only of long frequency modulated notes and no short or single notes. 3) The song chorus is dominated by adult males, while females add a great call. Males do not have a great call, unlike those in other gibbon species. There are no female solos. 4) The sound spectrum frequency is similar in adult males living in two different groups, but the duration of the first long note differed significantly between the groups. The sonic frequencies of male and female songs are lower than those of other gibbons: no more than 2 kHz. Hainan gibbon sound structure is simple, although females participate in the chorus, reflecting their primitive status among gibbon species.     

Longitudinal study of delayed reproductive success in a pair of white‐cheeked gibbons (Hylobates leucogenys)

Concern over a lack of breeding success in a pair of white‐cheeked gibbons (Hylobates leucogenys) prompted a four‐part study of gibbon behavior and physiology at the Lincoln Park Zoo. Data were collected to determine the female intermenstrual interval (IMI) and identify periods of peak receptivity. Subsequent behavioral data were gathered during both female menses and estrous periods to formulate a behavioral profile for each gibbon. The female experienced a species‐typical IMI of 21.6 days and exhibited heightened levels of behavioral receptivity toward the male during estrus. The male exhibited high levels of human‐directed behavior throughout the day. Closing the exhibit to visitors did not result in higher levels of social proximity or prosocial behavior between the pair, although it did eliminate the male's human‐directed behavior during the experimental condition only. The female exhibited higher levels of social grooming, solicitation of the male, and proximity to the male when the pair was locked indoors. Based on those findings, the pair was moved to an exclusively indoor exhibit. The female's visibility to the public decreased substantially in the alternate exhibit, but there were no other significant behavioral changes. Nearly one year after the exhibit change, the female gibbon was confirmed to be pregnant. Although the results of this study cannot be used to infer causal conditions that resulted in the pregnancy, they do support the notion that systematic documentation of animal behavior and physiology may be used as a tool for monitoring reproductive behavior and informing management decisions. Zoo Biol 21:413–434, 2002. © 2002 Wiley‐Liss, Inc.     

Singing behavior and singing functions of black‐crested gibbons (Nomascus concolor jingdongensis) at Mt. Wuliang,central Yunnan,China

We used data on loud duetted and solo songs collected from one habituated polygynous group of black‐crested gibbons (Nomascus concolor jingdongensis) on Mt. Wuliang, Yunnan, to test several hypotheses about the functions of these songs. The major functions proposed for loud gibbon songs include resource defense, mate defense, pairbonding, group cohesion and mate attraction. Duet bouts are generally initiated by adult males, who select the highest trees near to ridges or on steep slopes as singing trees. Such trees facilitate voice transmission and inter‐group communication. Singing trees tended to be located near important food patches and sleeping sites, which supports the resource defense hypothesis. The adult male and two adult females always sang interactively, alternating male phrases with the females' stereotyped great calls, to produce the duets, and females rarely produced great calls if they were more than 30 m from the male. The two females usually produced great calls synchronously during the duet, especially when they were close together. These features support both the mate defense and pairbonding hypotheses. The number of great calls and their degree of synchrony transmit information about spatial relationships and possibly pairbond strength to members to neighboring groups and floating animals. During or after the duet bouts, the adult females and juvenile moved toward to the adult male; and group members maintained a close spatial relationship, which supports the group cohesion hypothesis. Other incidents observed suggest a mate competition role for duets. The adult male always sang when the females started duetting with the subadult male. The subadult male sang solo bouts, but they were not more frequent or longer than bouts initiated by the adult male. Although mate attraction is the likely function of subadult solos, it was not convincingly demonstrated. In conclusion, all hypotheses concerning the function of singing are supported by at least some of the data, and none can be excluded. Am. J. Primatol. 71:539–547, 2009. © 2009 Wiley‐Liss, Inc.     

Within-group social bonds in white-faced saki monkeys (Pithecia pithecia) display male-female pair preference

White‐faced saki monkeys (Pithecia pithecia) lack most of the behavioral and physical traits typical of primate monogamy [Fuentes, 1999 ]. In order to determine if social bonds in this species reflect patterns displayed by pair‐bonded groups or larger multimale–multifemale groups, we draw on 17 months of data collected on wild white‐faced sakis at Brownsberg Nature Park, Suriname. We analyzed within‐group social bonds for three habituated groups (one two‐adult and two multiadult groups) by measuring grooming, proximity, and approach/leave patterns between adult and subadult group members. We found that both two‐adult and multiadult groups showed significantly stronger social bonds between a single male–female dyad within each group (deemed “primary dyads”). In all three groups, primary dyads were composed of the oldest adult male and a breeding female. These pairs had significantly higher levels of grooming than other within‐group dyads and were also in close proximity (<1 m) more often than nonprimary dyads. Grooming in primary dyads was nonreciprocal, and consistently biased toward female investment. Grooming patterns in nonprimary dyads varied, but were often more reciprocal. Grooming and proximity of the primary dyad also changed in relation to infant development. Our results suggest that while white‐faced sakis do not show behavioral and physical traits typical of monogamy or pair‐bonding, social bonds are strongest between a single male–female pair. Pitheciine social systems range from small group monogamy in Callicebus to large multimale–multifemale groups in Chiropotes and Cacajao. As the middle taxon in this platyrrhine radiation, behavioral strategies of white‐faced sakis provide a model for how social bonds and affiliation could be influenced by and affect the evolution of larger group size in primates. Am. J. Primatol. 73:1051–1061, 2011. © 2011 Wiley‐Liss, Inc.     

Detection of a New Hainan Gibbon (<Emphasis Type="Italic">Nomascus hainanus</Emphasis>) Group Using Acoustic Call Playback

Targeted management actions informed by robust data are needed to conserve species of extreme rarity, and assessing the effectiveness of different field methods for detection and monitoring of such species is a conservation priority. Gibbons are typically detected by their daily song through passive listening surveys, but lone gibbon individuals and low-density populations are less likely to sing, making detection difficult or impossible using standard survey techniques. Call playback represents an alternative potential method for detecting gibbon presence, but there has been no empirical evaluation of the usefulness of this method in the field. We investigated the efficacy of call playback as a survey method for detecting previously unconfirmed or unknown individuals of the Critically Endangered Hainan gibbon (Nomascus hainanus), the world’s rarest primate, in patches of good-quality forest outside the current home ranges of the three known Hainan gibbon social groups in Bawangling National Nature Reserve, Hainan, China. Call playback led to detection of a male-only call likely to have been made by a solitary male, and a previously unknown social group comprising an adult male, adult female, and an infant, increasing the number of known breeding females in the global Hainan gibbon population from five to six. Call playback therefore represents an effective tool for improved monitoring of Hainan gibbons, as well as other gibbon populations; however, it is a moderately disruptive survey technique, and should be employed sparingly, in key locations, and for short periods of time only when attempting to detect gibbon presence.     

Affiliative relationships and reciprocity among adult male bonnet macaques (Macaca radiata) at Arunachala Hill, India

In captivity, male bonnet macaques (Macaca radiata) frequently express "friendship" toward one another, including affiliative behavior such as huddling, grooming, coalitionary support, and sitting in close proximity. The purpose of this study was to determine whether wild adult male bonnet macaques also express "friendship" by investigating whether or not (1) adult male bonnet macaques have affiliative social relationships with other males, (2) the strength of social relationships varies among dyads, (3) there is time-matched reciprocity in allogrooming among dyads, and if so, whether the level of reciprocity occurs within a bout of grooming, a day, or over 2 months (the limit of this study), and (4) a correlation exists between the strength of social relationships and dominance ranks among adult males. Focal samples totaling 150 hr on all seven adult males in one study group were conducted to record both agonistic and affiliative interactions. Agonistic interactions were used to construct a dominance hierarchy, whereas affiliative interactions (sitting in proximity to within 1 m with and without grooming) were used to quantify the existence and strength of social bonds within dyads. Results show that adult male bonnet macaques had differentiated affiliative relationships with other males in their group. There was little reciprocity of grooming within a bout of grooming or within a day, but greater reciprocity over the study period of 2 months. There was no correlation between dominance ranking distance and the strength of affiliative relationship within dyads; however, within dyads lower-ranking males groomed higher-ranking males more than vice versa. This study suggests that friendships in male bonnet macaques are characterized not by immediate tit-for-tat reciprocal altruism, but by reciprocity over a longer time span, and that affiliative social relationships may be less constrained by agonistic relationships than is the case in more despotic species of macaques.     

Sex Differential Behavior of Immature Hanuman Langurs (Presbytis entellus) in Ramnagar, South Nepal

We investigated sex differences in the social behavior of immature Hanuman langurs (Presbytis entellus) in the light of sex-specifically different life-courses and Hanuman langur characteristics, such as the individualistic dominance hierarchy and the rarity of intragroup coalitions among adult females. We observed four immature female and four immature male langurs—all members of the same free-ranging multimale multifemale group in Ramnagar, South Nepal—from November 1992 to February 1993 for 288 hr via focal-animal and instantaneous sampling techniques. Immature females spent significantly more time in proximity to other group members than immature males did. They had more physical contact and groomed more. Other immature females were their preferred social partners. Immature males also preferred like-aged females. They restricted their relationships with other immature males to proximity and occasional grooming. Monitoring was directed especially toward adult males. Female behavior can be interpreted as oriented toward integration into the female social network and their age-inverted dominance hierarchy. Males seem to prepare for leaving their natal group and for future strong intrasexual competition.     

Evidence for High Variability in Temporal Features of the Male Coda in Müller’s Bornean Gibbons (<Emphasis Type="Italic">Hylobates muelleri</Emphasis>)

Most pair-living primate species engage in duets, wherein males and females produce coordinated vocalizations. Previous analyses of male gibbon contributions to the duet have shown that calls are individually distinct. Here we investigate variation in the temporal and spectral parameters in the male contribution to the duet, also known as the coda, of wild, nonhabituated male Müller’s Bornean gibbons (Hylobates muelleri), recorded both opportunistically and as a response to playbacks at the Stability of Altered Forest Ecosystems site in Sabah, Malaysia. We used linear discriminant function analysis to estimate the intra- and interindividual variation in 13 spectral and temporal parameters of the vocalizations (N?=?337) of 31 male gibbons. To further understand how call features vary within and between individuals we used a multivariate, variance components model to investigate how variance in features was partitioned at these two levels. We could identify males with a 66% accuracy using leave-one-out cross-validation, a relatively low score compared to female Müller’s Bornean gibbons and males of other species. We found that for some features (such as maximum frequency of the notes) most of the variance occurred between males, but for others (specifically total duration of the call and duration of rest in between notes) most of the variance occurred within a single male. Overall, male Müller’s Bornean gibbon coda vocalizations showed greater variability relative to their female counterparts, raising questions about potential differences in the function of the male and female contributions to the duet in Müller’s Bornean gibbons and the gibbon taxon as a whole.     

Social behaviour and infant carrying in a group of moustached tamarins,Saguinus mystax (primates: Platyrrhini: Callitrichidae), on Padre Isla,Peruvian Amazonia

The social behaviour of a group of eight moustached tamarins,Saguinus mystax, (five males, three females) was studied on Padre Isla in northeastern Peru. About 60% of all allogrooming was done by the two adult males in the group, and about 11% by a young adult female. All other group members groomed very little. The adult breeding female received more grooming than any other group member. After the death of the adult female (preyed upon by an anaconda) the amount of active allogrooming remained constant for all group members except for the young adult female, who increased her contribution to about 30%. Her preferred grooming partner was the subadult female, which generally screamed when being groomed by the young adult female and terminated grooming by going away. This kind of grooming relation is termed “forced grooming” and is interpreted as a possible social control mechanism. The young adult female groomed the adult males more often after the death of the adult female than before. This might have had the function of strengthening the social bond with the adult males and in obtaining the breeding position in the group. After the death of the adult female, the vulva of the young adult female grew to full adult size. Agonistic behaviour was less frequent than allogrooming. Most aggressive interactions (50%) originated from the subadult male of the group. The young adult female was the target of most of these aggressions. Extremely little aggression occurred between the three females. The young adult female was the only individual who tried to emigrate from the group during the study period. Her attempt to join a neighbour group failed due to rejection by all four members of this group. All group members participated in carrying an infant, but the adult males and the young adult female carried most frequently. Contribution to infant carrying varied with the infant's age.     

东黑冠长臂猿鸣叫声谱分析

2007 年9 月至2009 年6 月,利用Sony TC - D5 Pro2 录音机、Sony C - 76 指向性话筒和Sony 录音磁带对广西邦亮自然保护区3 群东黑冠长臂猿的鸣叫进行了录音,对每群录音效果较好的5 个声音用Signal/ RTS 4.0 软件进行声谱分析。结果表明:东黑冠长臂猿叫声的频率较高,最高频率已经达到甚至超过了5 kHz;雄性的鸣叫声由起始音(boom)、简单的重复音节(aa notes)、调节前音节(pre-modulated note)和调节音句(modulated phrases)组成,雌性长臂猿一般只会发出一种固定而刻板的激动鸣叫,二者互相配合组成结构复杂的二重唱。通常,二重唱由成年雄性发起和结束,并占主导地位。同时,将东黑冠长臂猿二重唱的声谱结构与近缘种西黑冠长臂猿和海南长臂猿进行比较,结果显示雄性和雌性的叫声、以及二者配合发出的激动鸣叫序列在三者之间都有明显差异。因此,从声谱特征角度可以有效论证这三种长臂猿独立物种的分类地位。     

Social relationships between adult females and the alpha male in wild tufted capuchin monkeys

Primates are notable for the widespread presence of long-term female-male associations which go beyond the mating context. However, little attention has been given to the factors that affect within-species variation in female-male relationships, especially among New World primates. Although detailed accounts of heterosexual relationships in Cebus species are scarce, a few studies have suggested the occurrence of strong associations between adult females and high-ranking males. This study explores affiliative relationships between females and the alpha male during the nonbreeding season in wild tufted capuchin monkeys (Cebus apella nigritus). Affiliative relationships were explored through female-male patterns of spatial proximity and grooming. By adopting a social network approach, we analyzed: (1) whether the alpha male is the preferred male partner for females and, (2) whether variation (if any) in female-alpha male affiliation can be explained through both female individual characteristics and social network metrics. Our results showed that alpha males were the favorite male partner for adult females in the proximity networks, but this did not hold true in the grooming networks. In addition, female-alpha male interaction patterns showed considerable variation, with only some females being strongly associated with the alpha male. Our results suggest that such a variation can be explained by female dominance rank, level of centrality (the quantity and intensity of spatial connection with other females) and prestige (the quantity of grooming received by other females) in female-female social networks. Taken together, these findings highlight two aspects of female-alpha male relationships in tufted capuchin monkeys: the alpha male represents the most socially integrated male in the group, and females with high dominance ranks and high centrality in both proximity and grooming networks show stronger relationships with the alpha male.     

Grooming interactions among adult chimpanzees at Bossou,Guinea, with special reference to social structure

Grooming and proximity interactions among chimpanzees at Bossou, Republic of Guinea, were analyzed as an index of friendly and affinitive relationships among adult males, among adult females, and between the sexes. Data from the first (1976–1977) and the third (1982–1983) study period were used. The expected value of their interactions was calculated from the number of adult males and females in the group and also from the observed frequency of combinations of adult males and females in the parties (temporary foraging groups). In the pooled data from the two periods, there was little difference between grooming and proximity (without grooming). The frequency of male-female grooming and proximity interactions was lower than expected, and that of female-female interactions was higher than expected. The frequencies of male-male grooming and proximity were intermediate but fluctuated. Male-male grooming frequency was lower than that recorded in chimpanzees of East Africa. Characteristics of same-sex affinitive interactions, especially between Bossou chimpanzee females, clearly differ from those of East African chimpanzees and are more like those recorded for female-related groups of Japanese macaques (Macaca fuscata).These differences indicate the variability and flexibility of chimpanzee social structure.     

Sociality in <Emphasis Type="Italic">Callithrix penicillata</Emphasis>: I. Intragroup Male Profile

We analyzed the social interactions and behavior of adult males from a group of black-tufted-ear marmosets (Callithrix penicillata) to determine their roles and hierarchy in the group and how their behavior fits within the predictions of monogamic or polyandric mating systems in callitrichines. We monitored 1 group of marmosets from February to October 2005 in central Brazil. We conducted focal subject samples with 20 predetermined behaviors for adult and subadult males and registered all occurrences of agonistic behavior, affiliative behavior, copulations, and alarm vocalizations. Moreover, we recorded the height in the vegetation and proximity to other individuals by the focal subject. Males exhibited no clear dominance hierarchy based on either behavioral data or patterns of scent marking. Copulation and grooming patterns showed a social bond between 1 of the males and the dominant female, suggesting him as the group’s putative breeding male, with no apparent competition for the position. There was no difference regarding other behaviors— alarm vocalization, infant carrying, and play—or the use of different vegetation strata among the males, and no indication of a specific role by the putative breeding male or any other male in the group. The presence of multiple males in marmoset groups and the behavioral profile generated in the current study suggest a mating system compatible with monogamy with helpers-at-the-nest structure.     

Differences in Titi Monkey (Callicebus cupreus) Social Bonds Affect Arousal,Affiliation, and Response to Reward

Titi monkeys (Callicebus cupreus) are a monogamous, New World primate. Adult pair‐mates form a bidirectional social bond and offspring form a selective unidirectional bond to their father. Some of the neurobiology involved in social bonds and maternal behavior is similar to the neural circuitry involved in nonsocial reward. Due to these overlapping mechanisms, social states may affect responses to external rewarding stimuli. We sought to determine whether having a social attachment, and/or being in the presence of that attachment figure, can affect an individual's response to a rewarding stimulus. In addition, we compared affiliative bonds between pair‐mates to those between offspring and fathers. Eighteen adult male titi monkeys were either living alone (Lone), with a female pair‐mate (Paired), or with the natal group (Natal; N = 6/condition). Each individual went through eight 30‐min preference tests for a sweet substance, Tang. For Paired and Natal males, half of the test sessions were with their attachment figure and half were alone. Lone males were always tested alone. Preference scores for Tang, time spent drinking, affiliative, and arousal behaviors were measured. Paired and Natal males emitted significantly more isolation peeps and locomoted more when tested alone compared to when tested with their attachment figure, and paired males engaged in more affiliative behavior than Natal males. Lone males engaged in significantly more behaviors indicative of behavioral arousal such as locomotion and piloerection compared to Paired and Natal males. Finally, Paired males drank significantly more Tang and had a significantly greater preference for Tang compared to Lone and Natal males. These results indicate that offspring undergo a behavioral separation response upon separation from their father that persists into adulthood, Lone males are more behaviorally reactive, and that living with an attachment figure and the type of attachment relationship result in different responses to a rewarding sweet stimulus. Am. J. Primatol. 74:758‐769, 2012. © 2012 Wiley Periodicals, Inc.     

The social behavior of a marmoset (Saguinus fuscicollis) group II: Behavior patterns and social interaction

The behavioral patterns and social interaction of a marmoset (Saguinus fuscicollis) group in a semi-naturalistic environment were observed for 14 months. The analysis showed that, of the 32 behavior patterns observed, the 10 most frequent accounted for over 97 per cent of the total behavior. One pattern, sit and look, accounted for 44 per cent of the total behavior. The two most frequent social behavior patterns, grooming and social play, were concentrated in different parts of the group. The focal point of grooming was the adult female; social play was characteristic of younger animals 4–20 months of age. These results were compared with other studies of marmosets and with primate studies on grooming and social play.     

Sex and age differences in juvenile social priorities in female philopatric,nondespotic blue monkeys

Juveniles should choose social partners on the basis of both current and future utility. Where one sex is philopatric, one expects members of that sex to develop greater and sex‐typical social integration with group‐mates over the juvenile period. Where a partner's position in a dominance hierarchy is not associated with services it can provide, one would not expect juveniles to choose partners based on rank, nor sex differences in rank‐based preferences. We tested these ideas on 39 wild juvenile (3.2–7.4 years) blue monkeys (Cercopithecus mitis stuhlmanni), cercopithecines with strict female philopatry and muted hierarchies. We made focal animal observations over 6 months, and computed observed:expected amounts of proximity time, approaches and grooming given to various social partners. Overall, our results agree with the hypothesis that juvenile blue monkeys target social partners strategically. Spatial proximity, approaches and active grooming showed similar patterns regarding juvenile social preferences. Females were far more sociable than males, groomed more partners, reciprocated grooming more frequently, and preferred—while males avoided—infants as partners. Older juveniles (5–7 years) spent more time than younger juveniles (3–4 years) near others, and older females were especially attracted to infants. Close kin, especially mothers and less consistently adult sisters, were attractive to both male and female juveniles, regardless of age. Both sexes also preferred same‐sex juveniles as social partners while avoiding opposite‐sex peers. Juveniles of both sexes and ages generally neither preferred nor avoided nonmaternal adult females, but all juveniles avoided adult males. Partner's rank had no consistent effect on juveniles' preference, as expected for a species in which dominance plays a weak role. Juveniles' social preferences likely reflect both future and current benefits, including having tolerant adult kin to protect them against predators and conspecifics, same‐sex play partners, and, for females, infants on which to practice mothering skills. Am. J. Primatol. 72:193–205, 2010. © 2009 Wiley‐Liss, Inc.