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BEHAVIOUR - Editorial Comment

Editorial Comment

(Editorial Overview Text Replicated on Overall Species page - Pan paniscus - Bonobo)
  • Female bonobos are sexually receptive for a greater proportion of the time than are female Pan troglodytes - Chimpanzees. In particular, adolescent females show prolonged receptivity, and females are sexually receptive until shortly before parturition (until about the last month of pregnancy) and return to cycling within about a year after parturition, despite not being fertile at this time. Copulation rates during oestrus are actually lower than for female Pan troglodytes
  • A variety of behaviours including approach, penile display, lead, bipedal standing, looking at and touching of the female by the male are seen prior to copulation. Bonobos copulate in both the dorso-ventral and the ventro-ventral positions, with more ventro-ventral copulations when the male involved is an adolescent, and a predominance of the ventro-dorsal position when an adult male is copulating with the female. It has been suggested that females prefer the ventro-ventral position but that adult males prefer the ventro-dorsal position.
  • There is an absence of male coercion of females to mate.
  • Copulation-for-food exchanges have been observed both in the wild and in zoo settings.
  • Additionally, bonobos use behaviours involving genital contact - genito-genital rubbing, non-copulatory mounting, rump-rump contact and manual touching of the penis - in the formation and maintenance of social relationships between individuals of the same or different sexes, including for reduction of tension and for reconciliation. See Bonobo Pan paniscus - Social Behaviour - Territoriality - Predation - Learning (Literature Reports) for further details.

(References are available in detailed literature reports below)

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Sexual Behaviour

Source Information

Note: many sexual-type activities in bonobos are not associated with reproduction but rather have social functions (B577.6.w6). These are described in Bonobo Pan paniscus - Social Behaviour - Territoriality - Predation - Learning (Literature Reports). Only sexual behaviours between adult males and adult females are considered here.
  • Copulation in bonobos is extremely promiscuous. (B577.6.w6)
  • At Wamba, copulation occurred while bonobos were feeding, resting or travelling. Copulation lasted from a few to 80 seconds, with 15-20 seconds the average duration. Of 106 instances, 66 were dorso-vental, 37 ventro-ventral with three starting dorso-ventrally and ending ventro-ventrally. When a female presented by backing towards a male, dorso-ventral copulation generally occured, but when a female sat in front of a male, gazed at him then fell onto her back and elevated her buttocks, ventro-ventral copulation occurred, After copulation the male usually remained in place while the female sometimes stayed in the same place (older females) or moved a short (older females) or longer (younger females) distance away. Often the male's penis remained erect. In 17 of 121 observed instances, a juvenile or infant was involved (the other partner being an adult); intromission generally occurred in copulations involving an immature male and an adult female. In two cases the female then moved to another place while carrying the immature individual on her back. Promiscuous behaviour was noted, the same female copulating with more than one male. Maximum tumescence of the female genitalia was observed for periods of as long as 11 and 12 days. Females with dependent offspring were seen copulating. On several occasions copulation had an obvious non-procreative function in that a female presented to a male who possessed a large fruit, and immediately following copulation, begged for and received food from the male. [1980](J583.9.w1)
  • Female bonobos are sexually receptive for relatively long periods - about twice as long as in Pan troglodytes - Chimpanzee. (B147)
  • Copulation between adult males and adult females may be initiated by either the male or the female. (B577.6.w6)
  • Courtship displays by males towards females include: (B577.6.w6)
    • The male facing a female who is too far away to be touched and spreading his thighs to expose his erect penis, then sitting or squatting, moving the body up and down, side to side or forwards and backwards. The chest may be stuck out or stooped forwards. The hands are extended and moved, most commonly forwards but in other individuals upwards or sideways. (B577.6.w6)
    • If the female fails to respond to the first display, approaching the female, sitting or bipedally standing in front of her, extending a hand and lightly touching the female or her head, shoulder, back or knee. (B577.6.w6)
    • Positive response from the female involves standing up, or standing and approaching the male if he is further away, then "presenting": exhibiting her genitalia to the male. (B577.6.w6)
    • If the female does not present, the male retreats several metres from the female and resumes courtship display. (B577.6.w6)
    • There may be several repetitions of courtship display, approach by the female, retreat and return to courtship display before copulation occurs. (B577.6.w6)
  • Females may initiate copulation by approaching and presenting to a male who has not shown any sign of courtship. (B577.6.w6)
  • Females in oestrus may approach to within a certain distance "not too close, but not too far, from the male"; if the male then is "fascinated by her swollen genitalia" and shows any courtship display, the female then approaches and presents to him: "In this situation we cannot say that the male initiated copulation." (B577.6.w6)
  • Presentation by the female may be:
    • Standing quadripedally, facing away from the male, thrusting her genital area in front of the male. This presentation is followed by dorso-ventral copulation. In this study at Wamba, most copulations were dorsal. (B577.6.w6)
    • Lying on the back in front of the male, raising her buttocks and showing her genital area to the male. this presentation is followed by ventro-ventral copulation. In this study at Wamba, 29.1% of copulations were ventro-ventral. (B577.6.w6)
    • In the study at Wamba, changes of position from dorso-ventral to ventro-ventral were noted on several occasions, initiated by the female. It was noted that the male was not always willing to mount in the ventro-ventral position and it was suggested that the dorsal position was preferred by males while the ventro-ventral position was preferred more by females. (B577.6.w6)
  • Ventral copulation occurs more in adolescents than in adults, and half of copulations between a female and an immature male were noted to be ventro-ventral (at Wamba). It appeared that females preferred the ventral position more than did males. (B577.6.w6)
  • In ventro-ventral copulation, the male takes a quadripetal position while the female passes her arms under those of the male, or clings to the male while turned onto her shoulder, and she grasps the male's hips with her legs; occasionally one or both of her hands grasps an overhead branch rather than the male. At least part of the female's weight is generally taken by the male. (B577.6.w6)
  • In dorsal copulation, the female often stands in a quadripedal position, limbs slightly bend, but sometimes lies prone, raises the buttocks only, stands with all four limbs fully extended, or sits facing away from the male. The male is generally in a bipedal standing slouch to sitting position, and often but not always he has one hand or elbow on the female's back. The female often extends a foot or hand and touches the male's scrotum, sometimes pressing firmly, increasing the male's thrusting pressure. (B577.6.w6)
    • A latero-ventral variation involves the female on her side or back with her legs around the side of the male's chest
  • On average, a copulatory bout lasts 15.3 seconds, with 2.7 thrusts per second and 43.8 thrusts per copulation (based on film taken at the feeding site at Wamba). (B577.6.w6)
  • It is common for a male to copulate several time a day, and ejaculation may not always occur; often the penis is still erect following copulation. (B577.6.w6)
  • Sometimes the female screams towards the end of copulation. (B577.6.w6)
  • Interference by other individuals is not common - seen in only 7% of cases at the Wamba feeding site (33/515 copulations). In 27 cases, an adult male interfered and in six cases, an adult female. Interference involved approach (11), intimidation (2) threat and pursuit (8), open-hand slapping (10) and squeezing between the partners (1). In the cases where a male interfered, he was dominant over the copulating male, who avoided or fled his approach. Sometimes with a young female, both would flee together, but most females reacted calmly or even aggressively towards the intruder. (B577.6.w6)
  • Juveniles often watch, cling to either party (belly or back) and scream. Not uncommonly, an immature individual will get between the copulating pair; this is tolerated. Juveniles show interest in copulations involving other females, not only their own mother, and after the partners finish copulating, the juvenile will often show immature copulation with one of the partners. (B577.6.w6)
  • Occasionally, sexually mature individuals (adolescents) also will respond to nearby copulation, with a male mounting the copulating male and thrusting, or mounting the upper of two females engaged in GG-rubbing, inserting his penis and thrusting. (B577.6.w6)
  • After copulation, both bonobos remain sitting together or calmly separate be several metres. (B577.6.w6)
  • Copulation occurs more in early morning (69%) in the period 0530 - 0900 under natural conditions. (B577.6.w6)
  • Copulations are often seen under conditions of excitement: when parties join, or when bonobos discover a large food source. Copulations occurring in the early morning may function as a greeting between male and female as they leave their night nests. Copulations at a feeding site may facilitate males and females feeding together. With provisioning at Wamba, obvious interactions involving females taking sugar cane from a male then presenting and allowing mounting by the male, and a case of a female inviting copulation then taking sugarcane from the male. (B577.6.w6)
  • Grooming between sexual partners immediately before or after copulation is uncommon (occurred in 9/515 copulations). (B577.6.w6)
  • Note: copulation commonly occurs under tension-filled conditions such as when parties meet, "suggesting that it plays a social role in preventing antagonism and facilitating peaceful coexistence between males and females." (B577.6.w6)
  • At the Wamba provisioning site, high-ranking males copulated more often than lower-ranking adult males or adolescent males. This could be explained by the fact that the subordinate males spent less time at the provisioning site. One particular low-ranking male who did spend long periods at the feeding site also showed a high frequency of copulation. (B577.6.w6)
  • While a top-ranking male is not able to monopolise a female, an oestrous female has been observed apparently selecting to mate only with one top-ranking male and not with any other males. (B577.6.w6)
  • Instances of a male forcing copulation on an unwilling female (rape) have not been observed in bonobos. (B577.6.w6)
  • Among females, the highest frequency of copulation occurred in young nulliparous females. Females with infants less than a year old showed the lowest frequency of copulation. Copulation occurs mainly when the genitalia are at or near maximum tumescence (swelling). This is seen in adolescent females nearly all the time; they have a period of about 5 - 6 years in which they are sexually receptive most of the time, but do not conceive (the period called "adolescent sterility"). Once pregnant, the sexual swelling decreases about two months prior to parturition and the female ceases copulating about a month before parturition. . Maximum tumescence may be regained as soon as one year after giving birth. The sexual cycle lasts about 46 days (captive data) and a female often shows a maximal or near-maximal swelling for 20 days or longer (although periods as short as three days and as long as 60 days have been recorded in different females. (B577.6.w6)
  • Unlike in Pan troglodytes, there is no evidence that male bonobos ever try to mate a female against her will, nor that they show consortship. It is suggested that female-female alliances, producing female-male co-dominance, has reduced the costs of sexual receptivity to female bonobos. (J611.4.w1)
  • Bonobos apparently use sexual behaviours for conception, paternity confusion, practice (sex with immatures), exchange for food or social benefits, and communication, including development of social relationships, tension reduction to avoid aggression, and repairing a social relationship following aggression. (J611.4.w1)
  • Female bonobos have a sustained sexual attractiveness; this is thought to affect their social status. Females remain sexually attractive for long periods including during pregnancy and lactation, when conception is not possible. At any one time, a relatively high proportion of female bonobos is interested in mating (compared to in Pan troglodytes - Chimpanzee). (B580.5.w5)
    • This makes it more difficult for a high-status male to monopolise mating opportunities, which in turn makes it less important for males to achieve high status. (B580.5.w5)
    • Male bonobos rarely compete for access to sexually receptive or proceptive females. (B580.5.w5)
    • Male bonobos treat receptive or proceptive females in a friendly way and the female chooses whether or not to mate. (B580.5.w5)
    • There is evidence of higher mating success in high-ranking males. (B580.5.w5)
      • High-ranking males have higher rates of paternity, as shown by DNA. (J179.266.w1)
  • Female bonobos engage in genital-genital contact and genital-genital rubbing with one another. (B580.5.w5)
  • Low ranking females initiate sexual contact with other females more often than do higher ranking females. (B580.5.w5)
  • Female-female genital contact may promote reconciliation and relieve social tensions, maintaining good relationships between the individuals. (B580.5.w5)
  • Sexual behaviour, in both males and females, is more frequent and more varied than in Pan troglodytes - Chimpanzee. (B580.5.w5)
  • Juvenile males "vigorously pursue sexual interactions with adult females", but not (except on very rare occasions) with their own mothers. (B580.5.w5)
  • Sexual behaviour of males starts at under one year of age, with the infant clinging to his mother's GG-rubbing partner after the adults finish GG-rubbing, and inserting his penis into her. In juvenile males, sexual behaviour is common, with the youngster running to adults who are copulating or GG-rubbing, clinging to the back or stomach of one of the adults and screaming. After the copulation/GG-rubbing has stopped, the adult will "embrace the juvenile and practice similar behaviors with him." Adult females in particular often will cooperate, such as lowering her hips to enable the youngster to insert his penis, or grasping his hips and inserting his penis. Other juveniles may come up and touch the female's behind, and she will generally allow each to copulate in turn. (B577.7.w7)
  • Males also, following copulation, will mount and thrust at male or female juveniles, but without inserting their penis, rather rubbing on the tops of the hips and the thigh. (B577.7.w7)
  • Juvenile females. whose genitalia have not yet started to grow, engage in sexual behaviour much less frequently. Females start GG-rubbing from about six years of age. (B577.7.w7)
  • In a group of bonobos at San Diego Zoo, copulation between the adult male and adult female was always ventro-ventral. The male always initiated mating by "penis presenting": squatting with legs spread and penis erect, oriented towards the female. The female would initially increase activity (locomotion, object manipulation), then after 30 - 60 s, approach the male, roll onto her back and slide under him; occasionally the male would "penis present" then approach the female. Mating occurred only when the female was in oestrus, as indicated by swollen genitalia. Copulation lasted on average 20 s, with about 25 thrusts. The male would mount (with an erection but without intromission) both infant/juvenile (female) offspring and would also mount these immature females dorso-ventrally without an erection, on occasions when the offspring presented her posterior to the male, backing up against him and rubbing her genital area against his scrotal area. (J576.20.w2)
  • Adolescent females are attractive to males, and are sexually receptive, over large parts of the sexual cycle. Parous females may resume cycling within a year of parturition and are sexually receptive for most of the oestrus cycle: in a study at Wamba, at any given time, 57 - 86% of mature females were sexually attractive/receptive. (J576.23.w2)
  • A study of three "old adult", four adult and three adolescent females in the E1 community at Wamba found that pregnant and females with newborn offspring were sexually inactive, but females with infants under that three years of age copulated as frequently as those without dependent infants. Copulation occurred mainly in the maximal swelling phase as indicated by greatest firmness of the sexual skin. Firmness rather than size of the sexual swelling was the best indicator. The copulation posture was ventro-ventral in 19.5% of copulations and was more likely to be ventro-ventral for adolescent rather than adult or old-adult females and for copulations involving juvenile or infant males rather than adult or adolescent males. Firmness of the sexual swelling showed periodic fluctuation; "old adult" females maintained maximum swelling for 3 - 22 days (mean 14.6 days, s.d. 7.4 days), out of a cycle length of 37 - 49 days (intervals between the last days of successive periods of maximum swelling). On average, 48.4% of females showed maximum swelling on any given day. One pregnant female and two with newborn infants showed regular swelling but rarely copulated; that is, while copulation generally occurred during the period of maximum swelling, not all females with maximum swelling were sexually receptive. One adolescent female was noted to show maximum swelling for very long periods but with copulation occurring only in more restricted periods. It was noted that some other studies had shown prolonged periods of receptivity in Pan paniscus females, in the non-maximal swelling phases as well as in the maximal swelling phase. Females are found in mixed parties even during non-receptive periods of the oestrous cycle and even when highly pregnant or with newborn infants. (J576.28.w1)
    • Male on female ventro-dorsal mounting could be distinguished from copulation by the lack of penile erection, intromission and/or thrusting, as well as its occurrence without preliminary solicitation normally seen as part of the bonobo copulation process; this occurred at any point in each female's cycle for most of the females (and for female Kame, the oldest female and a central point in group integration, mainly when she was in the lowest stage of firmness). This mounting appeared to act as greeting or for control of male excitement. (J576.28.w1)
  • In observations at Iyoko (yoku) marsh grassland near Yalosidi, copulations were always seen in larger parties containing more than 10 individuals. Of nine observed instances, six were dorsoventral and three ventroventral; three ventroventral GG-rubbing episodes were seen also; in none of the occasions where the ventroventral position was employed did the female underneath appear worried about turning on her back in the wet marsh. (J576.29.w1)
  • At Wamba, it was noted that the copulatory sequence usually starts with the female presenting, therefore it would appear she chooses the copulatory position, which is generally dorso-ventral with adult or adolescent males, but tends to be more often ventro-ventral with juvenile males. Common male behaviours prior to copulation include approach, penile display, lead, bipedal standing, looking at, nodding, turning, sitting with, following, branch-shaking , drawing back the shoulders, touching the shoulder or back, swaying the body, bipedal walking, stretching hand out and others. In some cases, the male allows the female to take food from him. Common female behaviours include approach, present, lead, turn, follow, look at, lip on the back, GG-rub with another females, sit-with, embrace, grimace, lie laterally, and less commonly vocalise, run approach, take food, bipedal stand, eat food. (J576.31.w3)
  • Observations of groups of bonobos in zoos have varied in their reports of proportions of ventro-ventral versus ventro-dorsal mounting, from nearly 100% to 53%, 32% and 3% ventro-ventral. Further analysis indicates both individual-based and age-based differences, with more ventro-dorsal copulation when fully adult individuals were involved. (J586.92.w1)
  • Compared to chimpanzees, female bonobos show more frequent and prolonged oestrus (days with maximal or semi-maximal perineal tumescence), which may result in less sexual competition between males. No possessive or consortship behaviours have been seen in Wamba bonobos. However, a study looking at male rank order within the whole community, party, and subparty (when the large feeding party was split into separate subgroups e.g. in different trees, at different patches of terrestrial vegetation), it was found that there was a weak correlation between copulation frequency and male ranking, and a clearer correlation between copulation rate and male ranking. (B586.10.w10)
    • In a given subparty, the top-ranking male within that subparty had clear mating priority. At the feeding site, copulation rate (number per hour) was highest for the two highest ranking males. Copulation frequency (number of copulations) was clearly higher for the four highest ranking males than for the three lower ranking males, while the adolescent males showed a lower copulation frequency than the top males, but higher than the lowest three adult males. Considering rank within subparties, temporary first-ranking males were responsible for 32% of total copulations at the fixed provisioning site, 54% under mobile provisioning and 41% under natural conditions, and either the alpha male or the highest-in-subparty male were responsible for 54%, 77% and 46% of copulations observed under fixed provisioning, mobile provisioning or natural conditions. (B586.10.w10)
  • A study comparing bonobos at Wamba with chimpanzees at Mahale and Gombe suggested that adult female bonobos do not show prolonged oestrus, with maximal swelling having a mean duration of 12.9 days and mean cycle length of 32.8 +/- 12.1 days (N=8). The majority of copulations (77% in E1 group, 67% in E2 group) occurred when females were in the maximal swelling stage, and they did not copulate more frequently than chimpanzees did, throughout the swelling cycle. However, females resume cycling within a year following parturition, therefore they do show higher copulation rates than chimpanzees if the whole inter-birth interval is considered. Adolescent females showed much higher copulatory rates than adult females, in contrast to rare mating between adolescent female chimpanzees and adult males, and appeared to have "attractivity" for adult males (since the males actively solicitated them for copulation). More copulations were initiated by males than by females (89% of copulations in this study), suggesting receptivity by the females; all copulations were opportunistic, without consortship or possessiveness. It this study there was no consistent relationship between male rank order and mating. Males showed copulation rates of 0.10 - 0.21/hour, lower than for chimpanzees, while adolescent males copulated 0.05 - 0.19 times per hour, again lower than adolescent chimpanzees. (B586.11.w11)
  • In a study at Wamba involving the E1 community, the following terminology was used. Copulation: "mounting with insertion of the penis and ejaculation between a mature [adult or adolescent] male and female." Other genital contacts between mature individuals included noncopulatory mounting, genito-genital rubbing and rump-rump contact. Mounting of a mature male by a mature female was considered noncopulatory if the male's penis was not erect, it was not inserted, or no thrusting occurred. Genital contact where one or both individuals were immature (under eight years of age) were considered as genital contact rather than copulation, even if the form of copulation was occurred between an immature male and a mature female. genital contact behaviours were seen involving bonobos from under one year of age and occurred between all age-sex classes except for being extremely rare for immature female with adult female. Genital contact between immature individuals usually (32/41 cases) occurred during play. Between individuals of the same age class, it occurred when they were in symmetrical contact - such hugging each other while hanging from branches. Between individuals of different ages, such contacts occurred during play such as an older individual carrying a younger individual on their belly. Immature males performed genital contact behaviours more frequently than did immature females, with more between male-male dyads than male-female or female-female dyads; it was considered this might be associated with the greater tendency of immature males than immature females to engage in social play. Genital contacts occurred more between siblings than between unrelated individuals, which was probably because immatures tended to stay with their mothers (therefore there is more opportunity to play with siblings than with unrelated immatures). Infants under two years of age only engaged in ventro-ventral genital contact, with ventro-dorsal contact first seen in infants of the two to four year age class, and increasing in proportion with age; females never mounted other bonobos, while males were both mounted and mounted others. Genital contact between immatures and adult males occurred less than that between other age-sex combinations (0.17 times/hour). Between mature males and infants, usually (five of six cases) the male held the infant so they were ventro-ventral and rocked them so their genitals rubbed together; this occurred as part of play. Between mature males and juveniles, this was not seen, and most genital contacts occurred during antagonistic interactions or in the excited period at the start of feeding; the context was the same as noncopulatory mounting and rump-rump contact between mature individuals - e.g. the immature individual, threatened by an adult male, would present towards him and be mounted. Noncopulatory mountings occurred quite frequently between a late-juvenile female and adult males. The only genital contacts between mature females and infant males under two years of age involved the mother holding her infant in ventral contact and rubbing the infant against their genitals; this usually occurred in a situation in which the female was stressed. With infants over two years old, genital contacts with adult females (usually, 59/61 cases, not their own mother) involved their active behaviour, most commonly with the immature male approaching a female which was involved in copulation or in other genital contact with a mature individual, and then having genital contact with her. Copulatory type genital contact occurred more with oestrus females, and sometimes involved insertion of the immature male's penis. Genital contact behaviours involving infants very rarely involved any courtship behaviours (bipedal standing, stretching hand, swaying back, display of penile erection) nor presenting behaviour. These behaviours were seen more as individuals grew older. As males reached adolescence, however, the frequency of copulation decreased drastically: at this age, young males tend to stay on the periphery of the party, as they receive aggressive behaviours from adult males; also, mature females are less likely to permit penis insertion by late juvenile or adolescent males without preceding courtship behaviour (which they do allow for younger immature males). The frequency of copulation increased again as they become young adult males, but was still lower than for juveniles. However, genital contact with mature males gradually increased to adolescent and became more frequent in adulthood. Immature females below the age of six to eight years showed lower frequencies than for males of similar ages. The one late-juvenile (six to eight years) female studied showed a high rate of genital contact with mature males, presenting to them for noncopulatory mounting in response to the aggressive behaviour which was often directed at her by the adult males; this may have been because she had recently lost her mother and needed more appeasement of others. Recently immigrated adolescent females tended to show both more genito-genital contact with adult females and more copulatory behaviour with males than did adult females. (J552.18.w2)
  • Observation of 53 copulation attempts among bonobos at Wamba found that males initiated most copulation attempts (97%) and showed approach or courtship behaviour starting more than 5m from females, In successful copulation attempts, copulation initiation behaviour by the male was followed by approach, leading and presenting by the female, while this did not occur in unsuccessful copulation attempts. The response of the female determined whether or not the copulation attempt was successful; in no instance was copulation forced, or interrupted by other bonobos. In a third of copulation attempts (11 or 31), males solicited copulation with females not in the swelling phase of the cycle, and half of these attempts (5/11) resulted in copulation, a lower proportion than in solicitation of females in their maximum swelling phase (18/21 attempts successful). (J576.45.w1)
  • Compared with chimpanzees Pan troglodytes, female bonobos are less likely to initiate copulation. (J576.47.w1)
  • Mating is mainly opportunistic and promiscuous, although consortship has been seen. DNA analysis using nuclear and mitochondrial DNA markers extracted from faecal samples showed that while matings of females with males from outside the community were not uncommon, resident males were the fathers of most of the offspring, Additionally, the highest ranking males had the highest paternity success. The presence of five different mitochondrial haplotypes among 15 adult females was consistent with the generally accepted finding that there is frequent migration of females between communities. (J179.266.w1)
  • Female bonobos appear to copulate more frequently than do female Pan troglodytes, if the whole of the inter-birth interval is considered, but show lower copulation rates than chimpanzees during the maximal swelling phase of the cycle. It was noted that while the copulation rate per male was similar for bonobos and chimpanzees, the number of males present per oestrous female was lower for bonobos than for chimpanzees (this would support the hypothesis that the lower copulation rate in oestrous bonobos is due to lower opportunity). Association of female bonobos with males does not appear to vary much depending on the stage of the cycle; this supports the hypothesis that oestrous female bonobos are less eager to copulate than are oestrous female chimpanzees. The inter-birth interval in bonobos shows greater variation than for chimpanzees. If it is assumed that a shorter optimal period for producing the next offspring results in less variance in inter-birth interval, then the observed greater variance in inter-birth interval for bonobos versus chimpanzees supports the hypothesis that bonobos have a longer optimal period for producing their next offspring; however data from the Tai forest may affect this. It is suggested that the costs to females of living in mixed-sex parties is lower in bonobos than in chimpanzees, due to their higher social status, feeding priority, and possibly differences in food availability such as increased patch size and the presence and use of terrestrial herbaceous vegetation, so that female bonobos with dependent offspring are not handicapped in access to food despite travelling more slowly, in contrast to female chimpanzees with dependent offspring. At Wamba, observations indicate it is not unusual for a female to have two dependent offspring simultaneously, with one carried ventrally and the older one on her back (two of nine females in group E1, 1990-1991, and two females in the neighbouring group P).(B587.11.w11)
  • Coercion and aggressive mate guarding do not appear to be factors in bonobo mating. (B587.15.w15)
  • In an initial study at Lomako, of 105 instances of sexual behaviour, mainly in trees (since bonobos rarely permitted observation when they were on the ground), there were 75 cases of male-female copulation as well as 25 instances of female genito-genital rubbing and five cases of male-male genital contact. The copulatory rate (heterosexual only) was 0.18/hour. Of the heterosexual copulations, 84% involved adult males, with 7% involving adolescent males, 8% involving infant males and only 1% juvenile males. Based on 42 cases where the state of the female's genital swelling was detected, copulations occurred through most of the oestrous cycle; no copulations were seen involving females in E0 (females with very young infants, or young adolescent females, but 28% involved E1 females (mothers and young females), with 57% involving E2 class and 14% involving E3 (maximally swollen) females. Females with dependent offspring were involved in 44% of copulations. Adult males rarely copulated in the ventro-ventral position (8/58 matings) while this position was seen in 10/12 copulations involving adolescents or younger males; overall, 26% of matings occurred ventro-ventrally. Seven of the eight ventro-ventral copulations involving adult males were with a female with dependent young. Mean duration of copulation was 12.2 seconds (range 1.5 - 45.0 seconds). Mating occurred most frequently during the morning feeding peak, and again during the period of feeding just before settling and building night nests. Courtship generally involved a male approaching a female to within 15 feet, then sitting and leaning back, displaying an erect penis and gazing at the female. Occasionally the male would shake a branch to get the female's attention. This posture was sometimes held for long times (18 minutes recorded). A receptive female usually would present to the male, backing up to him in quadrupedal position, limbs slightly flexed. The male then crouched or stood bipedally behind the female and mounted, followed by intromission and thrusting. Alternately, the female sat in the male's lap, or she lay prone, and he thrusted while in a sitting position. When a female presented ventrally she either leaned back, supported by branches, or lay on her back, legs around the male; in two instances the male was in the lower position during ventro-ventral copulation. Usually neither individual vocalised, but sometimes long squeals were heard from the female, and on one occasion the male carried out lip-smacking. In ventro-vental mating the two bonobos maintained eye contact; in dorso-ventral mating the female sometimes looked at the male over her shoulder. Sometimes the female held the male's testes. After thrusting, the couple separated, usually with one or both individuals moving away, but sometimes they groomed each other for a short time. It was noted than following copulation the male's penis often remained erect. Infants were often present (clinging to their mothers) during mating; other individuals, both subadults and adults, often moved towards copulating pairs. On one occasion a maximally-swollen female was mated by two adolescent males, one juvenile and an adult within five minutes. On two occasions female infants were seen to "approach a male, handle the male's genitals and rubbed their clitorides against them." This was tolerated by the males. Interference of mating by immatures appeared due to a desire to participate, not to disrupt. Genito-genital rubbing between females occurred most commonly during feeding (16 occasions) but also during travel (4), reunions between parties (2) and play between infants (3). Two mother-daughter instances were noted. All observed instances occurred in the trees. GG-rubbing involves: "Two females embrace face to face, stare into each other's eyes, and rub their genitals together in rapid, lateral movement. In general, on of the partners wraps her legs around the other's waist as they rub." It is normally performed silently, but "grinning" with full lip retraction, and vocalisation, has been observed during G-G rubbing. It appeared that females in sexual swelling states E1-E3 were attractive and responsive for GG-rubbing; GG-rubbing sometimes occurred in close temporal association with heterosexual mating. It has been suggested that GG-rubbing has a function of easing tensions during periods of group excitement. Male-male sexual contact involved dorsovental mounting, ventroventral monuting with pseudocopulation and rump-rump contat. Dorsoventral mounting between adult males was similar to dominance mounting seen in Pan paniscus. male-male ventro-vental mounting, with erect penises occurred between two juveniles and adult-adolescent, in quiet feeding situations with no apparent aggression. Rump-rump rubbing occurred between two adult males in a possibly appeasing context (subordinate male presenting to chasing dominant male). [1984](B596.13.w13)
  • Compared with Pan troglodytes - Chimpanzee, at any one time the proportion of females in oestrus is higher and the estrus sex ratio (ratio of the number of adult males to the number of adult females showing oestrus at a given time) is lower. This makes it more difficult for a dominant male to monopolise oestrous females, and other males can approach and solicit oestrous females. It is suggested that "Under such circumstances the most important thing for males is not to dominate other males, but rather to be preferred by females as copulation partners. This may be why males rarely attack or attempt to sexually coerce females. Females can easily ignore solicitations by alpha males, and the occurrence of copulation largely depends on whether females accept a male's solicitation." (J645.20.w1)
  • Captive data: In a group of bonobos at San Diego Zoo (adult male, unrelated adult female, two female offspring of five and three years of age), nearly all copulations were ventro-ventral. The male invited the female by "penis presenting": squatting, legs spread and erect penis conspicuous, body oriented towards the female. In response to this, the female would increase locomotory and object manipulation behaviours, then after 30-60 seconds, approach the male, roll onto her back and slide under him; copulation then occured. Occasionally the male would penis present and then approach the female. The male only mounted the female when she was in oestrus (genitalia swollen). (J576.20.w2)
  • Captive data: A study of a group of bonobos at Planckendael, Belgium, used focal animal sampling to look at sexual competition, with all occurrences of sexual activities or interventions involving the focal female being recorded. Over totals of 43 sexual interactions with Dzeeta (highest ranking female), 172 with Hermien and 70 with Hortense, interventions occurred on 5/43, 17/172 and 1/70 occasions respectively. Of the 23 interventions, 14 were performed by females, 12 of these being performed by the alpha female, Dzeeta, who interfered with sexual interactions between Hermien and Kidogo, and between Hermiene and Redy. Interactions were more commonly directed towards the male (18) than against the female (5); all interventions directed against females were carried out by females: four by Dzeeta against Hermiene, and one by Hortense against Hermiene. Of the interventions directed against males, Dzeeta carried out eight, Hortense, one, Desmond (highest ranking male), one, Ludwig, three, Kidogo, four and Redy, one. Hermiene showed a preference to mate with Redy, the son of Hortense, which is supportive of the suggestion made from observation of wild bonobos, that sons may benefit in access to females by the presence of their mother. All interventions directed at sexual encounters involving Dzeeta were carried out by males; during the period when she was the focal animal, she was the only female showing a regular swelling and menstrual cycle, and it was considered that this may explain efforts by males to prevent other males from mating with her. Interventions performed by females were considered to be an expression of female sexual competition. (J576.41.w1)
    • Note: Aggressive acts have been observed in captive groups by dominant females against subordinate females with young offspring, or against the infant: Dzeeta showed several occasions of fierce aggression against Hermiene when Hermiene had a newborn infant, and at another collection, the dominant female Kombote was seen throwing the nursing infant of another female, Diatou, against a wall. It was suggested that female infanticide could be "the most extreme form of female intra-sexual competition." (J576.41.w1)
  • Captive data: in a group of three adult females and three adult males at Twycross Zoo, the dominant male had almost exclusive mating access to the dominant female while she was maximally tumescent. However, her offspring was sired by the lowest ranking male, who mated with her more in the five days following the period of maximal swelling. The middle-ranking male mated with the lowest ranking female more frequently than did the other males, both when she was maximally tumescent and in the period following this, and was confirmed as the sire of her offspring. Overall, the middle-ranked male had the highest mating success and the highest ranking male mated slightly less often than did the lowest ranking male. For the five infants conceived before or during the study, the highest ranking male sired the first two infants, but did not sire any of the following three, once the other two males were sexually mature: two were sired by the middle-ranked male and the other by the lowest-ranked male. (J577.77.w2)
  • Captive data: For females at Apenheul Primate Park, Apeldorn, The Netherlands, observed over a period of about 12 months, overall, females participated in GG-rubbing at higher rates than they participated in copulation. Copulation occurred at higher rates during the period of maximum swelling than during other phases of the cycle, but this did not reach statistical significance. GG rubbing did occur significantly more in the maximum swelling phase (paired t-test, t = 3.074, n = 5, p < 0.05). There was no asymmetry overall in which individual invited GG-rubbing or in which partner was mounter versus mountee, although asymmetry did occur in some individual dyads; the alpha female, Jill, showed mountee or mounter GG-rubbing with different partners without any status-dependant pattern being evident. There was no significant correlation between grooming and GG-rubbing or between contact-sitting interaction and GG-rubbing, although there was a positive correlation between grooming and contact-sitting. It was considered possible that in bonobos, the sexual swelling might be a means of attractiveness among females, enhancing social integration among females. (J564.68.w1)
  • Captive data: In a group with three adult females and three adult males (observed 27-10-1992 - 26-03-1993), the lowest ranking female, Hortense, showed maximum swelling for more of the time than the highest-ranking female, Dzeeta (the middle-ranking female, Hermien, was pregnant and did not show maximal swelling). The greatest number of copulations involved Hortense, who had significantly more sexual interactions than randomly expected, while Hermiene had significantly less sexual interactions. More copulations with Hortense occurred when she was maximally swollen, while those with Dzeeta were randomly distributed over the swelling phases. Dzeeta neglected 39 presentations by males (67% of the 58 cases where a male tried to initiate sexual contact) compared with 80% for Hermien (37 neglected presentations)  while Hortense neglected only 15% (5 male presentations). For Dzeeta, in all cases where the initiator could be determined, the male initiated sexual contact, and this occurred in both maximally swollen and non-swollen states and for Hermien, 96% of cases involved the male taking the initiative, while for Hortense males took the initiative for only 27% of 122 cases and initiated only eight copulation s with her, all when she was maximally swollen. Males neglected 17 presentations by Hortense but only one (of two) by Hermien; Dzeeta never made a clear presentation to a male. In 73% of observed cases, Hortense took the initiative, including 55 cases when she was maximally swollen and 34 in other phases, and initiated 16 copulations when maximally swollen and five in other phases. There was receptivity by females in all stages of the cycle, with heightened receptivity in the lowest-ranking female during her period of maximal swelling. The lowest-ranking female was the least attractive to the males (as indicated by sexual initiatives by a male towards a female; she was more attractive during the period of maximal swelling. female proceptivity showed inverse relation to rank (highest proceptivity in the lowest-ranking female). The highest-ranking female was the most attractive to males, but showed the lowest sexual activity and controlled male sexual access. (D391.w3)
  • Captive data: Masturbation has been observed in captive bonobos, particularly associated with tense situations. Masturbation has been observed in bonobos when alone, in group situations, and during presentation for, or even during, genito-genital rubbing or intercourse. forms of masturbation seen in females include manipulating the clitoris with a hand or foot, or rubbing the clitoris on an object or the ground. In males, the erect penis is manipulated manually, sometimes until ejaculation. (D386.2.4.w2d) 

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Authors & Referees

Authors

Dr Debra Bourne MA VetMB PhD MRCVS (V.w5)

Referee

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