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In mammals, allogrooming is prominent in forming and maintaining social and cooperative relationships. Yet an animal's social time is constrained, which may limit its access to a large number of partners. Dunbar (1993, Behavioral and Brain Sciences, 16 (4), 681–694) proposed that human polyadic conversations, which allow access to several social partners simultaneously, evolved as a form of social grooming to circumvent this time constraint. In nonhuman primates, polyadic grooming (PG), in contrast to dyadic grooming, may similarly be a time-efficient way to maintain weak social relationships with many partners which can be important for group level cooperation. It remains unknown whether PG is used to fulfil specific cooperative needs by accessing numerous weakly bonded partners and increasing the number of partners accessed per unit of time. We compared the use and effect of PG between chimpanzees, Pan troglodytes, which are highly territorial and collaborative (especially males), and bonobos, Pan paniscus, which are less territorial and collaborative and in which females are the main co-operators. We carried out focal grooming observations in one bonobo and two chimpanzee communities in the wild. As predicted, chimpanzees engaged in more PG than bonobos. Surprisingly, males engaged in PG more than females in both species. While chimpanzees accessed more partners per minute of grooming than bonobos via dyadic grooming, PG increased the number of partners accessed per minute only in bonobos. Finally, chimpanzees primarily used PG with individuals who were close in rank and frequent grooming partners, whereas bonobos used PG with individuals who were distant in rank, close party associates and frequent grooming partners. We suggest that bonobo males use PG to enhance conspecific social tolerance and mate choice. The overall higher rate of PG in chimpanzees suggests that between-group competition may promote polyadic affiliation, which possibly reinforces group cohesion and coordination. © 2020 The Authors

Social interactions affect the transmission of many pathogens, but infections often induce sickness behaviours that alter those interactions. Vampire bats are highly mobile and social, engaging in frequent allogrooming, which is likely to facilitate pathogen spread. Sickness behaviour is known to reduce social associations, but the effect on physical interactions between associated individuals, such as grooming, is less understood. Here, we tested the effects of induced sickness behaviour on allogrooming in vampire bats, while holding association between individuals in groups constant. To experimentally induce sickness behaviour, we used injections of lipopolysaccharide (LPS) and saline controls in 13 female common vampire bats, Desmodus rotundus, housed in stable groups of two to four adult bats. LPS injection induced an immune response that mimicked illness. Circulating leukocytes and neutrophil:lymphocyte ratios increased, while body mass and activity decreased. While LPS-injected bats did not receive less grooming from their group mates, they dramatically reduced the amount that they groomed their partners. This reduction in social interactions illustrates that sickness behaviour can potentially change transmission rates by altering directed behaviours, even under conditions of constant close proximity. The ability to manipulate social behaviours under controlled conditions should also prove useful for experiments attempting to test mechanisms underlying cooperation.

International audience; Behavioural adjustments to predation risk may impose costs on prey species. While the vigilance–foraging conflict has been extensively investigated, other important fitness-related behaviours exclusive to scanning, such as grooming, have been overlooked. Yet, risk perception is expected to be more accurately assessed in these contexts as food-related parameters should not interfere. We studied individually recognizable impalas, Aepyceros melampus, and questioned the factors that shape maternal decision making in two exclusive components of maternal care with high benefits and costs: scanning for predators and grooming offspring to remove parasites. While studies generally infer prey alertness level, used as a proxy of risk perception, from the observed investment in vigilance, the vigilance–allogrooming context gave us the opportunity to directly assess alertness during the time spent head-up, and then to investigate its sources of variation and its consequences for allogrooming probability. We found a strong decrease in allogrooming probability when maternal alertness increased. Mothers were more alert in open (grassland) than in closed (bushland) habitats at a large scale. Increasing group size led both to lower maternal alertness and higher proportion of suckling time spent allogrooming, but only when surrounded by low vegetation, the reverse being true in high vegetation. Finally, mothers suckling female calves were more alert. Our results underline the determinant role of habitat, shaping both offspring predation risk and the relative conspicuousness or protective value of group mates. We discuss the potential fitness costs associated with the antipredator–antiparasite trade-off faced during maternal care. Our results suggest that prey behaviours other than foraging are essential to identify factors shaping risk perception.

Strong social relationships confer health and fitness benefits in a number of species, motivating the need to understand the processes through which they arise. In female cercopithecine primates, both kinship and dominance rank are thought to influence rates of affiliative behaviour and social partner preference. Teasing apart the relative importance of these factors has been challenging, however, as female kin often occupy similar positions in the dominance hierarchy. Here, we isolated the specific effects of rank on social relationships in female rhesus macaques by analysing grooming patterns in 18 social groups that did not contain close relatives, and in which dominance ranks were experimentally randomized. We found that grooming was asymmetrically directed towards higher-ranking females and that grooming bouts temporarily decreased the likelihood of aggression between grooming partners, supporting the idea that grooming is associated with social tolerance. Even in the absence of kin, females formed the strongest grooming relationships with females adjacent to them in rank, a pattern that was strongest for the highest-ranking females. Using simulations, we show that three rules for allocating grooming based on dominance rank recapitulated most of the relationships we observed. Finally, we evaluated whether a female's tendency to engage in grooming behaviour was stable across time and social setting. We found that one measure, the rate of grooming females provided to others (but not the rate of grooming females received), exhibited modest stability after accounting for the primary effect of dominance rank. Together, our findings indicate that dominance rank has strong effects on social relationships in the absence of kin, suggesting the importance of considering social status and social connectedness jointly when investigating their health and fitness consequences.

Vocal exchanges are predicted to serve a social bonding function by allowing conspecifics to ‘groom-at-a-distance’. If vocalizations play a role in bonding, then they should be mainly exchanged between the socially bonded group members, and thus display high social selectivity that characterizes other affiliative behaviours such as grooming. However, whether or not vocal exchanges are driven by social bonds remains unclear. We investigated vocal selectivity by studying the relationships between contact-calling networks and grooming networks in multiple free-ranging groups of ringtailed lemurs, Lemur catta. Lemur grooming interactions were socially selective and were directed towards only some of their group members. However, their vocal exchanges displayed even higher levels of social selectivity. Instead of exchanging vocalizations with each group member they groomed, lemurs reserved their vocal responses mainly for the group members whom they had frequently groomed. We tested this vocal selectivity through a playback experiment in which we presented lemurs' calls to their group. Lemurs responded only to the playbacks of the conspecifics whose calls they had responded to while free-ranging, confirming that selective vocal responses do not depend on proximal (i.e. visual or olfactory) cues from the vocalizing lemur. These robust relationships between grooming and contact-calling networks in lemurs, a species that lives in small groups where grooming frequency reflects bond strength, demonstrates that vocal exchanges indicate the strong social bonds between conspecifics. Contact calls may serve a bonding function in social species by allowing the strongly bonded group members to groom-at-a-distance when they are separated from each other.

Unidirectional grooming is a low-cost behaviour for which the groomer is repaid via kin selection or reciprocity. Return benefits can come in the form of increased probability of being groomed or social benefits such as coalitionary support. By contrast, the reasons for mutual grooming, which occurs when two individuals simultaneously groom each other, are not understood. In this study, we test three hypotheses regarding the function of mutual grooming among wild male chimpanzees, using 16 years of data. The social bonding hypothesis posits that mutual grooming promotes a return benefit by serving to strengthen and maintain social bonds, whereas the immediate investment hypothesis states that it functions as a signal to indicate willingness to invest in (continue) the grooming bout. The switching hypothesis states that mutual grooming results from overlap created when the direction of the grooming interaction is switched. The social bonding hypothesis was not supported: measures of association were not correlated with the probability of mutual grooming. We also found no support for the switching hypothesis, as mutual grooming was equally likely to occur without a switch in the direction of grooming as when a switch occurred. The immediate investment hypothesis was supported by our finding that bouts with mutual grooming (1) were longer, (2) contained a more equitable distribution of unidirectional grooming and (3) had more unidirectional grooming switches than bouts without mutual grooming. We conclude that male chimpanzees use mutual grooming to obtain short-term benefits in the form of prolonging a grooming bout, and suggest that mutual grooming thus represents a form of overlapping parcelling.

Explaining cooperative behaviour is a fundamental issue for evolutionary biology. The challenge for any cooperative strategy is to minimize the risks of nonreciprocation (cheating) in interactions with immediate costs and delayed benefits. One of a variety of proposed strategies, the raise-the-stakes (RTS) strategy, posits that individuals establish cooperation by increasing investment across interactions from an initial interaction. This model has received little quantitative support, however, probably because individuals of many social species engage in repeated interactions from a young age. In some situations, however, such as following conflicts, after prolonged absences or during social instability, established relationships may become unreliable predictors of future behaviour, creating an environment for RTS. We investigated grooming interactions among wild male chimpanzees, Pan troglodytes , testing RTS in these specific contexts. We found evidence to support the view that male chimpanzees employed RTS during social instability, but not under the other conditions. However, we also found that the duration of episodes (discrete parcels) of grooming was negatively related to aggression risk and in consequence suggest that the patterning of grooming interactions indicative of RTS was less to do with preventing cheating, and more to do with avoiding the elevated risks of intramale aggression during the period of social instability. We interpret the apparent support for RTS in our data as a by-product of the way chimpanzees cope with fluctuating (here, elevated then diminishing) risks of aggression. We suggest that social instability raises the stakes for grooming by creating a more hazardous marketplace in which to trade.

Allogrooming has hygienic and social functions. Moreover, anxiety is thought to be reduced in the first few minutes after a grooming interaction is terminated. Few data exist on postgrooming reduction in anxiety, and mostly concern the recipient of grooming and captive animals. We analysed whether anxiety is reduced after grooming and whether this reduction differs between the donor and recipient of grooming. We collected 10 min postgrooming and matched-control (PG–MC) focal data on the donor and recipient of the same grooming interaction in wild Barbary macaques. We recorded all the occurrences of self-directed behaviours (i.e. self-scratching and self-grooming) as these are reliable indicators of anxiety. The occurrence of self-directed behaviour was greater in PGs than in MCs for both the donor and recipient. This increase in postgrooming anxiety was more evident for the recipient than for the donor. The postgrooming increase in anxiety was not due to a higher risk of receiving aggression after grooming. Unlike previous studies, our results indicate that anxiety may increase after grooming in Barbary macaques. If so, the social and hygienic benefits of grooming may outweigh its short-term anxiety cost. Self-directed behaviour may increase because of the emotional response to the change in activity (e.g. from grooming to travelling) and/or frustration at the termination of grooming. Our findings highlight the need to investigate further the link between emotions and grooming.

Reciprocation is thought to favour altruism among nonrelatives. Three types of reciprocity have been proposed: direct, indirect and generalized. All three are theoretically possible, but their role in real biological systems is unclear. We concurrently examined the occurrence of direct, indirect and generalized reciprocity during grooming exchanges in longtailed macaques, Macaca fascicularis. The occurrence of the grooming monkey A gave B predicted the latency and occurrence of the grooming B gave back to A (direct reciprocity), the latency of the grooming A received from C (indirect reciprocity), but not the grooming B gave C (generalized reciprocity). The duration of the grooming monkey A gave B predicted the latency and occurrence of the grooming B gave back to A (direct reciprocity) but not the grooming A received from C (indirect reciprocity) or the grooming B gave C generalized reciprocity). Finally, monkeys directed overall more of their grooming to those individuals that overall groomed them more (direct reciprocity), but not to those that groomed other individuals more (indirect reciprocity); nor did monkeys that received overall more grooming groom others more (generalized reciprocity). Overall, we found strong evidence for direct reciprocity, limited support for indirect reciprocity and no evidence for generalized reciprocity. Our results support the view that direct reciprocity plays a crucial role in the life of primates and suggest indirect and generalized reciprocity are rare or absent in nonhuman animals. We argue that direct reciprocity may be driven by a system of partner-specific emotional bookkeeping of past social interactions that does not require complex cognitive capacities.

Promiscuous and repeated mountings by females are evolutionarily intriguing as females are expected to be choosy and matings are expected to be costly. We evaluate the evolutionary basis of these behaviours in a high-density population of European badgers. We analysed postpartum mounting behaviour, in 3 years, at two neighbouring social groups each year. We demonstrate a polygynandrous social mating system, with repeated mounting. Mounting was skewed among females in four social-group-years, but overall did not differ from random, potentially because female reproductive success is context dependent, varying with local food availability and femaleefemale competition. Some males mounted more than others; however, male mounting frequency was not related to dominance rank, self-grooming rate, or body condition index. Mounting frequency did not predict paternity success; furthermore, a 16-year genetic data set showed that paternity success was positively correlated with body condition index. Females may therefore mount with males that do not father their offspring to minimize the risk of infanticide from them. Females may also trade mountings for allogrooming from males, but mounting frequency did not vary with relatedness, aggression received from males or sequential allomarking by males. We conclude that promiscuous and repeated mounting in badgers may have evolved to reduce maleemale aggression around mounting and the likelihood of infanticide from males by masking paternity. Promiscuous mounting of female badgers does not devalue the previous male’s sperm, but may promote sperm competition, genetic diversity and genetic compatibility.

Biological market theory is an extension of the idea of reciprocal altruism, as a mechanism to explain altruistic acts between unrelated individuals in a more flexible system of exchanging commodities. In nonhuman primates, social grooming has been used to test predictions in both contexts: reciprocal altruism or biological markets. Specifically, in species in which males cannot coerce females to mate, males may attempt to interchange grooming for mating, particularly when females are fertile and mating opportunities are more likely to arise. We tested whether wild white-handed gibbon males from Khao Yai National Park, Thailand, increased their grooming activity when the female partner was fertile. Adult females and males of our study population are codominant (in terms of aggression), they live in pairs or small multimale groups and mate promiscuously. We analysed grooming episodes during 2760 observation-hours in 12 groups separately for females’ reproductive condition (cycling/pregnant/ lactating) based on noninvasive measures of ovarian hormone activity. We found that males groomed females more than vice versa and more grooming was exchanged when females were cycling than during pregnancy or lactation. The number of copulations/day was elevated when females were cycling, and females copulated more frequently with males on days when they received more grooming. When males increased their grooming efforts, females also increased their grooming of males, perhaps to equalize give and take. Although grooming might be reciprocated because of intrinsic benefits of receiving grooming, we conclude that males also interchange grooming as a commodity for sexual opportunities during a female’s fertile period.

Understanding cooperation between unrelated individuals remains a central problem in animal behaviour; evolutionary mechanisms are debated, and the importance of reciprocity has been questioned. Biological market theory makes specific predictions about the occurrence of reciprocity in social groups; applied to the social grooming of mammals, it predicts reciprocity in the absence of other benefits for which grooming can be exchanged. Considerable effort has been made to test this grooming trade model in nonhuman primates; such studies show mixed results, but may be confounded by kin effects. We examined patterns of reciprocity within and across bouts, and tested predictions of the grooming trade model, among wild male chimpanzees, Pan troglodytes: a system with negligible kin effects. In accord with the model’s expectations, we found that some grooming was directed by lower- to higher-ranked individuals, and that, on average, higher-ranked individuals groomed more reciprocally. We found no support, however, for a prediction that more reciprocity should occur between individuals close in rank. For most dyads, reciprocity of effort occurred through unbalanced participation in grooming bouts, but reciprocity varied considerably between dyads and only a small proportion showed strongly reciprocal grooming. Despite this, each male had at least one reciprocal grooming relationship. In bouts where both individuals groomed, effort was matched through mutual grooming, not alternating roles. Our results provide mixed support for the current grooming trade, biological market model, and suggest that it needs to incorporate risks of currency inflation and cheating for species where reciprocity can be achieved through repeated dyadic interactions. 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. Altruistic acts are behaviours that benefit the recipient at an apparent cost to the actor (Trivers 1971). The theory of reciprocal altruism holds that such acts can evolve by natural selection if the roles of actor and recipient are reciprocated such that both incur costs (albeit offset in time) and obtain net fitness benefits. Evidence for the role of this ‘direct reciprocity’ in shaping altruistic behaviour among animal species is limited, however (Clutton-Brock 2009). Originally modelled using the Prisoner’s Dilemma (Trivers 1971), increasingly sophisticated game-theoretical approaches have been developed to accommodate more realistic assumptions. In the Prisoner’s Dilemma, individuals are constrained into interacting with a particular partner, and have only a choice between cooperation or noncooperation, with the value of cooperation equal to both partners (Trivers 1971). In contrast, for animals living in social groups, choice of partners for social interactions is common (Wilkinson 1984; Noe et al. 1991; Emery 2004; Connor 2007

In social mammals, grooming is used not only for hygienic purposes; it also serves social functions. We examined the grooming patterns of dominant males in groups of cooperatively breeding meerkats, Suricata suricatta, to test the hypothesis that the distribution of grooming reflects the value of social relationships. Grooming between dominant individuals was the most commonly observed interaction. Grooming by the dominant male was less common when the dominant female was in oestrus. Grooming between dominant males and subordinates was asymmetrical, with dominant males receiving more grooming and providing less grooming to subordinates. Because subordinate males defend the group against extragroup males, the dominant male was predicted to groom subordinate males more often than to groom subordinate females. Although the sex of a subordinate did not affect the probability of grooming occurring, dominant males groomed subordinate males for longer than they groomed subordinate females. The duration of grooming by a dominant male was longer in small groups than large groups, suggesting that grooming activity is constrained by time. In contrast, subordinates groomed dominant males for longer in larger groups, and as a result, the asymmetry of grooming exchanges was exaggerated in larger groups. This result is consistent with the biological market theory, which predicts that the value of subordinates is dependent on group size and that subordinates will alter grooming efforts accordingly. These results suggest that meerkat grooming serves several social functions, such as the maintenance of valuable and/or fitness-enhancing relationships.

A social hierarchy is generally assumed to exist in those mammalian societies in which the costs and benefits of group living are distributed unevenly among group members. We analysed infrared closed-circuit television footage, collected over 3 years in Wytham Woods, Oxfordshire, to test whether social groups of European badgers have dominance hierarchies. Analysis of directed aggression between dyads revealed linear dominance hierarchies in three social-group-years, but patterns within social groups were not consistent across years. Dominance hierarchies were significantly steeper than random in five out of six social-group-years. In those social-group-years where a linear hierarchy was determined, there was an effect of sex on dominance rank, with females gaining significantly higher rank than males in two social-group-years. Overall, rank was not related to age, nor did it appear to affect the likelihood of an individual being wounded, or an individual's breeding status. The latter resulted from nonorthogonality between sex and breeding status, as there were only two breeding males. Overall, hierarchies were primarily dominated by breeding females, and may occur when breeding competition arises. Relatedness, unreciprocated allogrooming and sequential allomarking were not consistently related to levels of directed aggression across social-group-years. We suggest that dominance structures within European badger groups may be context dependent, with future study required to complete our understanding of where, and when, they arise.

Social grooming is a commonly observed affiliative behaviour in primates. Grooming has been suggested to represent a service in a biological marketplace, exchanged either for grooming or for other social commodities or services. Accordingly, grooming is predicted to be approximately reciprocated within a dyad when no other services are being exchanged, but it should be more asymmetrical if partners have different quantities of other services to offer. We analysed 412 grooming bouts observed in four groups of free-ranging redfronted lemurs to test this prediction. Grooming in this species seems to take place in a highly reciprocal manner because partners usually alternate in the roles of groomer and gromee within a grooming bout. However, within dyads there were asymmetries in the duration of grooming given and received. In both sexes, more grooming was directed from low-ranking towards high-ranking individuals than vice versa, and in males this asymmetry became more pronounced as the number of subordinates per group increased. Grooming in bisexual dyads was generally skewed in favour of males, but patterns of grooming between the sexes were less clear than within the sexes. In addition, aggression occurred at high frequencies between classes of individuals that were characterized by nonreciprocal grooming, suggesting that grooming may serve as a means to reduce aggression in dyads with a high potential for conflicts. Taken together, our results indicate that a strict reciprocation of grooming can be offset by power differentials between partners, where grooming appears to be traded by subordinates in exchange for the tolerance of dominants.

In primate sexual relationships, males and females can cooperate through social trade. Market-like trading of sexual activity has been theorized, but no data have yet been presented that clearly show its existence. I collected data to test whether biological market theory could account for exchanges of male-to-female grooming and sexual activity in longtailed macaques. I explored male-to-female grooming, rates of sexual activity, and groomingemating interchanges, which were male-to-female grooming bouts that directly involved mating. Male-to-female grooming mainly occurred when females were sexually active, and males groomed females longer per bout when mating, inspection, or presentation of female hindquarters was involved. Moreover, male-to-female grooming was associated with an increase in female rates for all forms of sexual activity, where in contrast, female-to-male grooming was associated with decreased rates of mating in the groomed males. Males did not preferentially mate with swollen females or invest more grooming in them during groomingemating interchanges, as swellings did not seem to be a reliable indicator of female fertility. Rank status was correlated with grooming payment during groomingemating interchanges in favour of higher-ranked males and females. In support of a biological market interpretation, the amount of grooming a male performed on a female during groomingemating interchanges was related to the current supply of females around the interaction. The results provided evidence of a groomingemating trade that was influenced by a mating market.

The presence of young infants influences female primate social behaviour, in particular social grooming, which may be exchanged for infant access within a biological market place (Henzi & Barrett, 2002, Animal Behaviour, 63, 915–921). Although social grooming is common among Old World primate species, it is rarely observed in a number of New World primate species, including spider monkeys. We investigated whether affiliative behaviour is exchanged for infant handling among wild female spider monkeys, Ateles geoffroyi yucatanesis. Occurrences of approaches, grooming and embraces received by 15 adult females were compared when they had infants less than 6 months old (‘mothers’) and at all other times. The occurrence of grooming was not influenced by the presence of infants. However, females received significantly more approaches and embraces when they were mothers compared to all other times. As mothers, they received significantly more embraces than they gave indicating that the increase in friendly behaviour received was due to increased interest from other females and not simply a general increase in sociality. The exchange of embraces for infant handling was subject to a market effect as the proportion of embraces given to mothers followed by infant handling decreased when fewer infants were present in the group. Although spider monkeys use embraces as the primary means of gaining access to infants, whether embraces provide long-term benefits to the recipient, remains to be determined. Thus, embraces may only serve to signal benign intent and reassure mothers during tense interactions such as infant handling.

In social mammals, grooming may be used in care of offspring, to maintain pair bonds, or to placate dominant individuals. We examined grooming patterns in groups of the cooperatively breeding meerkat, Suricata suricatta. Dominant females produce over 80% of litters, but older subordinate females occasionally breed. Grooming between dominant individuals was the most common and symmetrical interaction. The dominant female received more and gave less in grooming interactions with subordinates. The dominant female groomed younger subordinates more frequently than older subordinates, suggesting that grooming by dominant females represents parental care, and also reflects the reproductive conflict between females. Older subordinates groomed the dominant female more frequently than did younger subordinates. Subordinates that were frequently attacked by the dominant female groomed her for longer durations than those that were not, and the duration of dominant female grooming by subordinates increased as birth of the dominant female's pups approached. These results support the idea that subordinates use grooming to placate the dominant female. Analysis of 'immediate reciprocity' (whether the groomee returned grooming of the groomer within the grooming bout) showed that subordinate females reciprocated more frequently than subordinate males when the dominant female initiated grooming. However, the dominant female reciprocated subordinate females less frequently than she did subordinate males. This suggests that the need to placate the dominant female may be higher for subordinate females than for subordinate males, possibly because of the risk of eviction caused by reproductive conflict between females.

The social cohesion hypothesis of play asserts that the adaptive function of social play is to strengthen affiliative ties between group members, thereby increasing cohesion within the social group. Although this hypothesis is frequently cited, it has never been quantitatively tested. I used data collected from a wild population of cooperative mongoose (the meerkat, Suricata suricatta) to test four predictions arising from the hypothesis: first, that an individual's frequency of play, and mean number of play partners, will be positively correlated with group size (because individuals in large groups must strengthen ties with a greater number of animals); second, an individual's frequency of play will be positively related to frequency of other affiliative interactions such as allogrooming; third, an individual's frequency of play will be positively correlated with level of contribution to cooperative group activities (based on the assumption that individuals that are closely bonded to their group will invest more heavily in the group than those with weak ties); and finally, an individual's frequency of play will be positively correlated with duration of tenancy in the natal group. The behaviour of young meerkats failed to fulfil any of these predictions, and I conclude that social play is unlikely to have the capacity to promote social cohesion in mammals.

Classical models of grooming predict that subordinate primates will direct grooming towards dominants to receive coalitionary support from them. In contrast, recent reviews suggest that grooming asymmetries can change with social system and ecological conditions and should reflect asymmetries in services provided by different members of the dyad. We studied grooming patterns between females in six wild groups of common marmosets, Callithrix jacchus, to investigate the relation between social structure and grooming between females in a cooperatively breeding species. We observed grooming frequently and consistently in all study groups. Breeding females groomed nonbreeding females more than vice versa, and grooming between breeding and nonbreeding females was not related to agonistic behaviour. Our results provide some support to the hypothesis that grooming asymmetries are related to differences in services provided by different group members. We suggest that, in cooperatively breeding systems, breeding females may use grooming as an incentive for helper females to stay in the group.

The parcelling model of reciprocity predicts that grooming partners will alternate between giving and receiving grooming within grooming bouts, and that each partner will perform approximately as much grooming as it receives within each bout (‘time matching’). Models of allogrooming based on biological markets theory predict that individuals of lower dominance rank will exchange grooming for tolerance from high-rankers, and therefore an inverse relation will be found between grooming partners' dominance rank distance and how closely they match each other's grooming contributions within each bout. We used weighted logistic regression and weighted least-squares regression to test these predictions using data from female white-faced capuchins, Cebus capucinus, and bonnet macaques, Macaca radiata. Only 5–7% of macaque grooming bouts, and 12–27% of capuchin grooming bouts, were reciprocated. However, (1) the duration of grooming by the first groomer significantly predicted whether the groomee would reciprocate at all, and (2) when bouts were reciprocated, the duration of grooming by the first groomer significantly predicted the duration of grooming by the second groomer. Grooming was most balanced among females of similar dominance ranks. Both the time-matching and rank-related effects were weak, although significant. These results indicate that although some form of time matching may be a general characteristic of grooming in female-bonded primate species, time matching accounts for relatively little of the variation in the distribution of grooming within bouts. We also draw attention to weighted regression as a technique that avoids pseudoreplication while using all available data.

We used data from a natural experiment on adult female chacma baboons, Papio cynocephalus ursinus , to test the hypothesis that variation in aggression through time influences patterns of grooming reciprocity within a social group. Owing to a change in the baboons' competitive regime, we were able to compare data from periods when aggression was high (period 1) and low (period 2). During period 2, the slope of the relationship between aggression and rank was significantly shallower than during period 1 and less aggression was directed at the lowest-ranking females suggesting there had been a reduction in the dominance gradient. We attributed this to reduced effectiveness of dominance as a means of excluding other females from feeding resources. The reduction in aggression during period 2 was accompanied by an increase in grooming reciprocity between dyads suggesting that high-ranking females no longer attracted grooming by subordinates in exchange for tolerance, and that grooming in period 2 was exchanged for its intrinsic benefits. The loss of rank-related effects on grooming reciprocity in period 2 compared with period 1 further confirmed this. These findings show that female baboons are able to respond flexibly and swiftly to changes in their social circumstances and that a dynamic approach to primate social interactions is worth pursuing. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .

Stumptailed macaques, Macaca arctoides, are characterized by high levels of postconflict affiliative contacts between opponents. We investigated the occurrence of postconflict affiliative contacts between opponents and third parties that were not involved in the original conflict. We collected 10-min focal observations during postconflict and control periods in which we recorded all aggressive and affiliative behaviours between opponents and third parties. We distinguished three types of third parties depending on the relationship with the focal animal: own kin, opponent's kin and individuals unrelated to both opponents. We analysed the interactions with third parties separately, while distinguishing two classes of affiliative behaviours: (1) allogrooming and contact sitting and (2) sociosexual behaviours (e.g. genital inspection). The macaques showed differences between postconflict and control periods in their affiliative contacts with third parties. Aggressors received more postconflict grooming and contact sitting from their opponents' kin, received more sociosexual behaviour from their own kin and unrelated individuals, and directed more sociosexual behaviour to unrelated individuals. Victims received and directed less postconflict grooming from and towards their own kin. They received more postconflict sociosexual behaviour from all partners except their own kin and directed more sociosexual behaviour to all partners except the opponent's kin. This study establishes the occurrence of multiple postconflict triadic affiliation in stumptailed macaques, and is the first to show that victims receive contacts from third parties in a cercopithecine species, a behaviour previously described only in chimpanzees. It also highlights the importance of analysing the different affiliative behaviours separately in postconflict situations. Otherwise, many of the patterns we report, especially those involving victims, would have been missed.

Seyfarth (1977, Journal of Theoretical Biology,65, 671–698) proposed a model of social grooming among female monkeys that has had an enormous influence in the primatological literature. To test this model, I reviewed published data on primate grooming behaviour, using meta-analytical techniques. An analysis of grooming behaviour in 27 different social groups belonging to 14 different species revealed that a significant role in the distribution of grooming was played by attraction to high-ranking animals, attraction to kin and competition for grooming partners. These results confirm the majority of the predictions of the model. The need for more observational data on grooming (and other affiliative interactions) in New World monkeys, and experimental data on the relations between the exchange of grooming and the formation of agonistic alliances, is emphasized.

Lactating female chacma baboons, Papio cynocephalus ursinus, maintain close associations, or ‘friendships’, with particular males that may protect infants from sexually selected infanticide by a newly immigrated alpha male. In a 2-year study, we sought evidence of female–female competition for male friends in cases where two mothers maintained friendships with the same male simultaneously. In this context, relative competitive abilities of the rival females influenced social access to the shared male friend: dominant females maintained higher levels of close proximity and allogrooming with the male than their subordinate counterparts. This disparity was greatest when younger dominant females and older subordinate females shared a male friend. This pattern resulted from social displacement: subordinate females experienced a significant decrease in time spent near the male friend immediately after a dominant female began associating with him (but the converse was not true). Changes in time male–female friends spent near one another were due primarily to changes in the behaviour of the females. Females may compete for friends based on male rank and probability of paternity of their current infants. Evidence that lactating females may pursue alternative anti-infanticide strategies besides friendship formation came from two sources. First, subordinate females displaced from a friendship made compensatory changes in their relationships with the potentially infanticidal alpha male: spatial proximity and the rate of contact with him fell significantly in the period immediately following displacement. Second, across the entire sample of friendships, female social behaviour and age were significantly correlated. Compared to younger mothers, older females showed: (1) a smaller relative contribution to maintaining close proximity to the male friend; (2) less close proximity to the male friend; and (3) greater proximity to relatives (this association applied to higher-ranking females). Thus, avoidance of infanticidal threat and protective association with maternal kin may constitute two alternative counterstrategies for some lactating females.  2001 The Association for the Study of Animal Behaviour

In nonhuman primates, affiliative behaviours, such as social grooming and various forms of body contact, become more frequent after an aggressive interaction. Since such behaviours lead to a decrease in postconflict aggressive behaviour and displacement activities and to increased social tolerance, they have been labelled reconciliatory. We videofilmed sessions of free play in daycare centres in Stockholm and investigated whether affiliative behaviours used by 5-year-old boys in the postconflict period had a similar reconciliatory function. For 219 conflicts in 21 h 40 min of observation we recorded postconflict affiliative/prosocial, aggressive and displacement behaviours. When affiliative behaviours were shown and accepted by the opponent, aggressive and displacement behaviours decreased and play was promoted. These behaviours thus serve a function similar to reconciliatory behaviour in nonhuman primates and we think it is applicable to call accepted affiliative behaviours in postconflict periods of preschool children reconciliatory. However, conflicts were often polyadic and nonconflict periods consisted of intense play with a rich exchange of affiliative behaviours. These factors were limitations to the postconflict/matched-control method traditionally used in primatological research to document reconciliatory behaviour. We suggest that for preschool children, video recordings and an analysis and description of postconflict affiliative, aggressive and displacement behaviours can be used instead. Copyright 1999 The Association for the Study of Animal Behaviour.

This study focused on two aspects of the dynamics of reconciliation in stumptailed macaques, Macaca arctoides. First, we investigated the combined effects of multiple variables (i.e. sex, age, rank, conflict intensity, outcome, or number of participants, interopponent distance, kinship and friendship) on the occurrence of reconciliation. Second, we investigated whether opponents used different behaviour patterns in their postconflict reunions depending on the characteristics of their conflicts or their relationship with their opponents. We studied a multimale, multifemale group of 38 stumptailed macaques housed in a large outdoor compound. Three types of data were collected: (1) instantaneous scan sampling of contact sitting to infer 'friendship'; (2) ad libitum data on bared-teeth and teeth-chattering displays to infer dominance rank; (3) 10-min focal observations during postconflict (PC) and matched control (MC) periods in which we recorded interopponent distance at the beginning of the observation and all aggressive and affiliative behaviours between former opponents. Our study confirmed the high conciliatory tendency of stumptailed macaques previously reported for other groups. A stepwise logistic regression revealed that initial interopponent distance in PC, friendship and kinship were the only factors that independently contributed to explain the occurrence of reconciliation. Two main clusters of postconflict behavioural patterns emerged: allogrooming+contact sitting and sociosexual behaviours (e.g. hold-bottom). It is hypothesized that postconflict allogrooming and contact sitting may be used for the maintenance of valuable relationships, whereas sociosexual behaviours may be used more indiscriminately by any pair of opponents as a buffering mechanism to prevent immediate recurrence of aggression. Copyright 1999 The Association for the Study of Animal Behaviour.

Observations of captive female brown capuchin monkeys in five groups revealed that grooming is primarily the occupation of dominant females at both the individual and dyadic levels. When categorized according to rank class, alpha females were the only class to perform significantly more grooming than they received. These results are inconsistent with reports on vervets, baboons and macaques, and suggest that grooming in capuchin monkeys may have different functions from those reported for cercopithecine primates. A dyadic analysis revealed, however, that grooming occurred more often between closely ranked females, similar to what is seen in several Old World monkey species. Therefore, some aspects of grooming in capuchins are similar to that seen in Old World monkeys, but the way they distribute grooming is different, which may prompt a re-evaluation of current theories regarding the social function of allogrooming in non-human primates.

Allogrooming behaviour was analysed in a wild group of tufted capuchin monkeys, Cebus apellain Iguazu National Park, Argentina. Evidence is provided that allogrooming in this platyrrhine species serves an important social function, as has been demonstrated for catarrhine primates. Using ad libitum sampling, 654 grooming sessions were recorded during 740 contact hours with one group. Seasonal variation was found in daily time allocation to allogrooming and the mean duration and reciprocity of sessions. Individual dominance rank was an important determinant of grooming relationships. The dominant male and female were the most actively involved in grooming. Among adults, dominant individuals were involved in more sessions than were subordinate individuals. The females maintained strong grooming relationships with each other and tended to reciprocate more within sessions than did males. Oestrous females engaged in more grooming bouts with adult males than did non-oestrous females. Females with newborn infants were attractive social partners for the remaining members of the group. A social function for allogrooming in Cebus is indicated by the close relationship between allogrooming, the social system and coalition formation, and by the changes in quantity and direction of grooming in response to oestrous behaviour and to the birth of infants.

Grooming is among the most commonly performed parasite defence behaviour patterns and is eVective in removing ticks. Because both tick infestation and grooming activity have a cost, natural selection should favour individuals that match the current level of tick threat with an appropriate level of tick-defence grooming eVort. To test this notion, the relationship between seasonal tick challenge and grooming rate by wild, free-ranging impala, Aepyceros melampus, was investigated in Zimbabwe. Adult ticks in the vegetation showed a dramatic decrease from the warm/wet season to the hot/dry season, declining from 2·4 ticks per drag sample and 58 ticks per removal plot to virtually nil. This decline was mirrored by an associated decline in grooming rate by all impala in which self-oral and scratch grooming bouts per h decreased 30-45%. Allogrooming encounters per h (corrected for lying-down time) and total allogrooming delivered, as measured by bouts or episodes delivered per h, decreased for males but did not change for females. Overall percentage of time spent in all forms of grooming declined 37-57%. Multiple regression analysis revealed that, with the seasonal eVects of temperature and rainfall held constant, self-grooming rates were significantly and positively correlated with adult tick challenge, indicating that impala adjusted self grooming to seasonalfluctuations in adult tick threat. Allogrooming delivered was influenced by nymphal tick challenge; because the larvae and nymphs of the most abundant tick species favour the ear and neck region (where allogrooming is concentrated), allogroom- ing appears to function to remove immature ticks from body regions inaccessible to self-oral grooming. These results are what would be expected if grooming serves to remove ticks before they can attach and engorge, and supports the view that grooming is an evolved response to the threat of excessive tick burden in the impala's natural environment. ? 1995 The Association for the Study of Animal Behaviour

Abstract. It is commonly suggested that the principal function of allogrooming is to reduce social tension between group members, but direct evidence of the physiological consequences of grooming at particular sites is lacking. By filming allogrooming sequences in a herd of Camargue horses, Equus caballus , their preferred grooming site, which lies on the lower neck, was identified. Experimental imitation of grooming at this site reduced the heart rate of the recipient while grooming on a non-preferred area did not, in both adults and foals. This preferred site lies close to a major ganglion of the autonomic nervous system.

Abstract. Motivation for participation in social grooming differs for juvenile and adult primates in female-bonded social systems; juveniles attempt to develop social relationships as a means of integration into the group, whereas adults attempt to maintain relationships with other adults. Juveniles should therefore seek grooming relationships with adults but adults should be relatively uninterested. The local resource competition hypothesis predicts that grooming relationships between adults and juveniles should occur primarily within matrilines and should be negatively correlated with aggressive interactions. Alternatively, grooming relationships may depend on the ability of juveniles to provide additional services, such as assistance in aggressive interactions and allomaternal care. Grooming interactions of juvenile and adult female wedge-capped capuchin monkeys, Cebus olivaceus, were predictably asymmetric. Juveniles approached and groomed more than adults, whereas adults terminated grooming sessions more and often failed to reciprocate grooming. Juvenile-adult grooming was inconsistent with patterns predicted by the local resource competition model. Dyads of closely related females did not groom more than unrelated dyads and there was no relationship between rates of grooming and aggression. Frequency and duration of grooming was significantly correlated with frequency of allomaternal care given by juveniles. Frequency of grooming also correlated with rates of alliance formation by adults and juveniles. Juveniles provided agonistic support during alliances twice as often as adults supported juveniles. The structure of grooming indicated that juveniles were the primary beneficiaries of grooming relationships with adults. Juveniles provided grooming services to adults and provided additional benefits of allomaternal care and agonistic support during aggression. In return, juveniles were integrated into the adult social structure in the group.

Abstract. Adult female wedge-capped capuchin monkeys, Cebus olivaceus , exhibit a variety of grooming relationships; females groom frequently and reciprocate grooming, groom infrequently with non-reciprocating lower-ranking partners, or fail to form grooming relationships. Females have different motivations for avoiding or engaging in grooming that relate to the benefits derived from the interaction. These benefits include, but are not limited to, spatial proximity, alliance formation, access to a female's infant, and redirecting aggression. A test of Seyfarth's (1977, J. theor. Biol. , 65, 671-698) rank-related attractiveness model for grooming showed that adult female wedge-capped capuchin monkeys differed from many cercopithecine species in that grooming was directed down the dominance hierarchy and was not more frequent among adjacent-ranked females. Frequency of grooming was significantly correlated with frequency of approach and alliance formation. Grooming appears to have two underlying social functions, affiliation and appeasement. Affiliative grooming involves reciprocated grooming sessions in which relative rates of grooming are balanced. Affiliative grooming occurs more frequently among females in large groups than in small groups but the duration of grooming sessions is similar. These grooming relationships are significantly affected by the ranks of the females in the dyad; dyads composed of high-ranking females or a high- and middle-ranking female groomed more frequently and tended to reciprocate grooming. Grooming interactions classified as appeasement tend to be short unreciprocated sessions initiated by the higher-ranking female and terminated by the lower-ranking female. These grooming interactions are characteristic of females that avoid other group members and may reflect attempts by females to redirect potential aggression by soliciting grooming. Females with new infants also do not reciprocate, and usually terminate, grooming interactions. High-ranking or closely related females may groom a mother as a means of gaining access to a new infant.

Abstract. Two contrasting models were examined, each of which predicts a relationship between space and aggression in primates. A 'spatial density' model predicts that as spatial densities increase aggressive responses also increase. A more recent 'coping model' suggests that, over long periods of time, animals will adapt to crowded conditions by increasing appeasement behaviour and allogrooming to reduce social tension and the incidence of aggression. This study evaluated these models within the context of a traditional short-term crowding experiment by examining changes in behaviour when a well-established group of 61 rhesus macaques, Macaca mulatta, was periodically crowded into a familiar area one-fifth the size of its normal enclosure. Data from a sample of 20 adult subjects of both sexes showed that no significant increases in intense aggression occurred. Only mild forms of aggressive behaviour increased under the crowded conditions (threat and rough behaviour) and increases in rough behaviour were highest towards infants. Submissive behaviour such as avoidance and the bared-teeth display increased during crowding, and increases in the bared-teeth display were highest between same-sexed adult partners. Analysis of the rank distance between the performer and recipient of bared-teeth displays indicated that increases were most pronounced from the lowest- to the highest-ranking animals. Crowding produced a general increase in huddling with a corresponding decrease in grooming, and these changes across conditions were mostly attributable to interactions among kin. Results provide only partial evidence for both models and indicate that neither one by itself is adequate to explain behaviour in short-term crowding situations. Under short-term crowding, this group appeared to adopt a conflict-avoidance strategy rather than a more active tension-reduction strategy.

The extent of chewing on plastic ear tags was used as an indirect measure of the cumulative affiliative experiential history of red foxes, Vulpes vulpes , living in the city of Bristol, U.K. Tags were chewed by other foxes during social grooming, and the teeth marks left by animals with milk or permanent teeth were scored separately. Fewer adult dog foxes than females had tags chewed by cubs, but of those that did, the level of chewing was not different between males and females. The level of tag chewing by adult foxes on non-dispersing adult females was greater than for non-dispersing males, indicating that the females are more closely bonded to the social group. The lower level of adult chewing on the tags of dispersing adults suggests that decreased levels of grooming by adult foxes are associated with adult dispersal. For cubs, there was a strong negative relationship between affiliative behaviour with littermates during the first 13 weeks of life and future dispersal behaviour of male foxes, although there was no such relationship for females, suggesting that the social factors acting on dispersing females occur later in life. These results support the hypothesis of Bekoff (1977, Am. Nat. , 111 , 715–732). The value of such an indirect approach for monitoring affiliative behaviour in elusive species is discussed.

Adult female and male impala engage in a type of allogrooming in which partners alternately deliver bouts of oral grooming to the head and neck. These grooming encounters comprise typically six to 12 tit-for-tat-like exchanges of bouts and are highly reciprocal among adult females, adult bachelor males and subadult males. Although allogrooming among females could be between related individuals, that occurring among adult males would appear to be between unrelated individuals. Unlike allogrooming reported for some primate species and other ungulates, the dominant impala received no more grooming than the subordinate. It is proposed that one function of impala allogrooming is to reduce the ectoparasite load on body areas an animal cannot reach with its own mouth. The impala reciprocal allogrooming system is unique among free-ranging antelope and other ungulates and may be a candidate for the tit-fortat strategy of evolved cooperation.

Grooming in ungulates has been shown to be very effective in removing ectoparasites. Ectoparasites, especially ticks, may be costly to an animal's resources in terms of blood removed and depression of appetite. There are two opposing models that address the parasite-control of function of grooming: (1) animals may groom in response to stimulation from parasite bites, whereupon those with the most parasites should groom the most; or (2) animals may groom prophylactically, removing parasites such as ticks before they attach, as a reflection of a central programming or timing mechanism. Based on behavioural observations of Thomson's gazelle, Gazella thomsonii , Grant's gazelle, Gazella granti , impala, Aepyceros melampus , and wildebeest, Cannocheates gnu , in Kenya and at the San Diego Wild Animal Park (SDWAP), both models seemed to apply to different aspects of grooming. Presumably, as a reflection of their increased vulnerability to ectoparasites through a greater body surface to mass ratio (body-size principle), Thomson's gazelle were found to groom more frequently than wildebeest. This corresponds to a reportedly smaller number of ticks per m 2 surface area in Thomson's gazelle. Territorial males groomed less frequently than conspecific females and bachelor males, presumably relfecting their need to remain vigilant over females (vigilance principle). Within-species grooming was less in a low-parasite environment (SDWAP) than in a high-parasite environment (Kenya), reflecting both a decreased exposure to parasites (habitat principle) and a decrease in programmed grooming. Impala, which typically inhabit tick-infested woodland areas, orally groomed themselves more than the size-matched Grant's gazelle comparison species, and also engaged in a unique form of reciprocal allogrooming of the head and neck. That the impala allogrooming may also have a tick-removal function was supported by the finding that impala scratch-groom the head and neck less than Grant's gazelle.

Reciprocity and interchange of grooming and coalition formation of captive chimpanzees, Pan troglodytes, were studied at a group level as (partial) correlations between an actor matrix and a receiver matrix. Periods in which one male clearly occupied the alpha-position and those in which his position was unclear, because not all males behaved submissively towards him, were distinguished. Males appeared to reciprocate grooming in both types of period, but reciprocated support in conflicts only when the alphaposition was unclear. This may reflect a directly selfish strategy. In periods with a clear alpha-male position, males supported more often those they groomed more frequently, suggesting a social bond. In addition, males interchanged grooming for received support, but this seemed to be a by-product of correlations of each variable with received grooming. Correlations with dominance rank were notable: the higher the rank of the partners the more often males supported them. Further, males also more frequently received support and opposition by intervention from higher ranked partners. Grooming and support relationships of females were the same whether or not the alpha-male position was clear. Grooming appeared to be reciprocated and was associated with support, indicating a social bond. Furthermore, the correlation for interchange between grooming and support received was found to be genuine, but the reverse correlation between support and grooming received was not. Thus, interchange occurred in one direction only. Neither males nor females reciprocated opposition by means of aggressive intervention.

Reciprocal allogrooming is a unique but frequently performed behaviour of adult female and bachelor male impala, Aepyceros melampus (Hart & Hart 1992) and is a distinctive feature of newborn impala fawns (Mooring & Hart 1992). We have previously argued that the evolution of this behaviour appears to be related to its effectiveness in controlling ticks on the head and neck which are areas that an impala cannot reach with its mouth by self oral grooming. There appears to be no influence of kinship or dominance in choice of allogrooming partners or in the distribution of allogrooming between partners within an encounter (Hart & Hart 1992; Mooring & Hart 1993), and Hart & Hart (1992) have proposed that in impala, reciprocal allogrooming may represent one of the few bona fide examples of evolved cooperation in a non-primate species. The proposal of a behavioural system as a type of evolved cooperation necessitates the designation of benefits to the recipient and costs to the donor. The benefit of allogrooming to the recipient may be extrapolated from the value of self oral grooming in the removal of ectoparasites (reviewed in Hart 1990). The possible costs involved in delivering allogrooming include energy used, time taken from foraging, loss of water in saliva used in grooming, wear on the lateral incisors and distraction from vigilance for predators. The first three costs are likely to be small. Vertical attrition of the lateral incisors used in grooming has been shown, and these worn teeth subsequently become less efficient in removing ectoparasites (McKenzie 1990). The purpose of this study was to explore whether allogrooming appears to have a measurable effect on vigilance for predators. Within a group, a loss of vigilance would increase an animal’s susceptibility to predators. FitzGibbon (1989) found that cheetah were more likely to prey upon the less vigilant of a pair of Thomson’s gazelle. If stalked by predators, such as lions, wild dogs, hyenas or leopards, impala that take longer to alert to the predator are more likely to be killed. In the herd life characteristic of impala, overall individual vigilance might be expected to decrease as a function of increased group size (Underwood 1982). However, to take advantage of increased efficiency of vigilance in larger groups, the animals must be able to watch group mates for signs of reacting to a predator. Allogrooming activity would be expected to obstruct visual tracking of group mates, as does preening by dunlin, Calidris alpina (Redpath 1988). In our study of free-ranging impala, the plan was to examine the latency to alert to a predator for both the ‘allogroomer’ (delivering grooming) and the ‘allogroomee’ (receiving grooming), as well as the alert latency of non-allogrooming impala in the same group. To obtain this degree of control of the predator stimulus, and accurately record the alert latency, it was necessary to conduct the experiment with a person approaching a group of impala as a simulated stalking predator. We carried out observations on Fothergill Island, Matusadona National Park, Zimbabwe, during the tick-dense time of the year (March 1994) when allogrooming is common. Impala at Fothergill are preyed upon by lion, Panthera leo, cheetah, Acinonyx jubatus, leopard, Panthera pardus, and occasionally hyena, Crocuta crocuta, but are habituated to safari vehicles. We conducted observations from 0600 to 1100 hours and from 1630 to 1900 hours. The procedure involved driving a vehicle up to a herd of female impala to within 50–100 m of the nearest animals, waiting 1 min for the animals to adapt after the engine was turned off and focusing a video-camera on the group. As soon as a pair of impalas started to allogroom, we turned on the camera, and 3 s later passed a signal to the camera as a second investigator silently left the vehicle and began walking slowly towards the herd, ‘stalking’ until both *To whom all correspondence should be addressed.

Primates use social grooming to service coalitions and it has been suggested that these directly affect the fitness of their members by allowing them to reduce the intrinsic costs associated with living in large groups. We tested two hypotheses about the size of grooming cliques that derive from this suggestion: (1) that grooming clique size should correlate with relative neocortex size and (2) that the size of grooming cliques should be proportional to the size of the groups they have to support. Both predictions were confirmed, although we show that, in respect of neocortex size, there are as many as four statistically distinct grades within the primates (including humans). Analysis of the patterns of grooming among males and females suggested that large primate social groups often consist of a set of smaller female subgroups (in some cases, matrilinearly based coalitions) that are linked by individual males. This may be because males insert themselves into the interstices between weakly bonded female subgroups rather than because they actually hold these subunits together. © 2001 The Association for the Study of Animal Behaviour.

Summary The Macropodiae are the most social marsupials, and the whiptail wallaby is the most social macropod. This report describes the behaviour of whiptails and compares it with that of other macropods and of grazing ungulates, the macropods' colsest ecological equivalents elsewhere. The whiptails were studied in northeastern New South Wales from October 1966 to November 1967. This is an area of ridges and valleys, partly cleared, and grazed by cattle. The whiptails were found in open Eucalyptus forest and adjoining pasture. Field observations were made of three discrete mobs of up to fifty members each. The East end mob was studied intensively: each member was named, aged and sexed, and all gains and losses were recorded throughout the year. Less intensive observations were made of the Tank 1 and Ringbark hill mobs. Whiptails share a variety of postures and gaits, including bipedal hopping, with other macropods. Autogrooming with the mouth and feet was conspicuous, both as a utilitarian activity and as a conflict act in social situations. These whiptails were strictly grazers and did not drink. They were most active at dawn and dusk, and of all the macropods yet studied, whiptails are the most diurnal. Whiptails are alert animals with excellent vision and hearing. When alarmed they panicked easily and dashed wildly off in erratic, criss-crossing courses. During flight the hind feet produced a loud thump on the first few hops, an alarm signal shared with most other macropods. The principal predators on wallabies today are the introduced dingo and fox, which have replaced the marsupial wolf on the Australian mainland. The whiptails shared their grazing areas peacefully with several other species of macropods, but were occasionally displaced by cattle. The mobs contained all ages and sexes throughout the year, but seldom if ever were all members of a mob together at one time. Typically, they were split into continually changing subgroups of fewer than ten animals. Emigration of sub-adult males was observed, and there was evidence of emigration or differential mortality of adult males. Communication was primarily through visual signals, and an analysis of these shows remarkable convergence with the displays of ungulates. In accordance with the whiptail's unaggressive nature, threat and submissive displays were less well developed than superiority and courtship displays and conflict activities. Olfaction was primarily used for individual recognition and for sexual checking. Auditory signals are poorly developed in macropods generally. Whiptails show a positive gregarious tendency and a significant lack of overt interaction at close quarters. Social grooming was mostly restricted to mothers and their offspring. Fights between males consisted of ritualized pawing bouts. These bouts established a dominance hierarchy which functioned only to determine access to oestrous females. Recognizable social roles and co-operation were virtually absent. Breeding occurred throughout the year. Whiptails become sexually mature at about 18 to 24 months, but males probably had no opportunity to mate until they were 2 to 3 years old because of the sub-adults' inferior social status. Females typically mated late in their joey's pouch life. Fertilization was apparently followed by two months of embryonic diapause. Then gestation resumed for about one month so that the next young was born as soon as the previous joey vacated the pouch permanently at the age of 9 months. This pattern is similar to that of the Eastern grey kangaroo but differs from most other macropods, which have a postpartum oestrus and a longer embryonic diapause. The origin and function of embryonic diapause in macropods are poorly understood. Sexual checking of females and anoestrous courting were the most conspicuous interactions between adults. Oestrous courting was limited to a few days around the female's receptive period, which lasted only a few hours. Persistent following by the alpha male and several secondary males, wild mating chases, and copulation were diagnostic of oestrous courtship. Joeys typically began leaving the pouch late in the 8th month, became young-at-foot a month later, and were weaned by the 15th month. Mothers were not very solicitous or protective of their young. Females might remain loosely associated with their mothers for years, but males left the mob or became completely independent within it by their 21st month. Play consisted mostly of solitary chasing; social play except with the mother was almost non-existent. All types of play were less common than in other social mammals. Each mob had a home range of about 100 ha, which overlapped slightly the ranges of other mobs. All of the mob's range was occupied by all sexes and ages, but probably no individual occupied 100 per cent of the mob range. Males were generally wide ranging, while some females were sedentary. Females occupied smaller areas when their joeys were vacating the pouch. The most heavily used areas were flats with grass, close to woods or ridges. Whiptails probably benefit from limited clearing and pasture development, but large-scale habitat destruction has reduced their numbers overall. Members of adjacent mobs mingled peacefully in the overlap zones, but mostly kept to their own undefended ranges. Thus most of each mob's range qualified as a monopolized zone, or functional territory. Individuals of one mob occasionally visited in another mob's range, and several sub-adult males changed mobs. Field studies of mammalian societies have revealed a number of correlations between social organization and adaptations such as habitat preferences, activity cycles, and food. These generalizations seem to apply to macropods as well, but most macropods have never achieved either the other adaptations which encourage sociality, or an advanced stage of sociality itself. As diurnal, grazing inhabitants of rather open cover, whiptails are apparently at the peak of macropod social development. Their chief benefits from group behaviour are probably facilitation of mating and especially group vigilance and warning. Their social system also keeps the number of conspecifics regularly encountered to a manageable, recognizable level. The first macropods were probably solitary, nocturnal forest dwellers; the evolution of social organization in the family is obscure, but probable progressive stages are represented by the musk kangaroo, the quokka, and the whiptail.

Grooming patterns and the amount of social grooming occurring during daylight hours between herd members were recorded. Age and body weight were positively related to the giving of social grooming, as were age, body weight, milk weight, and milking order to the amount of social grooming received. The two members of a monozygotic twin pair have a similar social grooming rank with respect to the rest of the herd and the preferred partner of a herd member for social grooming is its twin. Social grooming may be used to uncover an affiliative or epimeletic scale of social distance within the cow herd as an alternative to scales of social distance based on agonistic encounters.

This study was aimed at evaluating diurnal and climatic influences on allogrooming in a small captive group of Java monkeys ( Macaca fuscicularis ). Allogrooming showed a definite diurnal cycle similar to those preeviously reported for other Macaca species. The major amount of allogrooming was recorded between 1300 hours and 1500 hours with a second minor peak occurring between 1100 hours and 1200 hours. The lowest mean levels were recorded in the early morning and in the late afternoon. Climatic factors were shown to influence allogrooming: more allogrooming was done under conditions of high temperature and low relative humidity. On the basis of the discrepancy between this latter finding and that previously reported for Japanese macaques ( Macaca fuscata ) living under similar conditions, it is suggested that the sensitivity of Java monkeys to climatic factors may be a species-specific trait.

In previous research, male chimpanzees (Pan troglodytes) were found to be more ‘conciliatory’ than females, in that after aggressive incidents males more often engaged in socially positive contact with former opponents. The first part of the present paper presents similar results for a large breeding troop of rhesus monkeys (Macaca mulatta). To investigate further the possible sex difference in postconflict behaviour, a series of experiments was carried out on small isosexual groups of young rhesus monkeys, three male and three female groups. Food competition was created by providing either a single apple piece (Monopoly test) or a handful of small pieces (Equality test). Observations lasted for 30 min, and behaviour in tests without food provisioning was also recorded. The predicted response to food was an increase in aggression followed by restorative behaviour, such as grooming. In Equality tests both sexes showed similar responses, i.e. increased aggression and decreased grooming and cohesiveness. In Monopoly tests, however, their responses differed. After the aggression increase, which occurred in all groups, males showed a significant increase in grooming and cohesiveness, whereas females showed the (non-significant) opposite trend. Another sex difference was that changes in grooming and aggression frequencies were related to the rank order in female groups, but not in male groups. Since there was no evidence for a direct causal connection between grooming and aggression, a new model is introduced which links grooming behaviour to the type of food provision rather than to the social disturbance by aggression. According to this model inequality in food distribution causes social tensions. Males actively try to reduce these tensions, whereas females do not. Some alternative explanations are also discussed.

Wild kangaroos were observed in north-eastern New South Wales, Australia. They were tolerant of each other, and coexisted peacefully with other macropods and cattle. Ritualized fighting occurred between males. Social grooming was rare, but anoestrous courting was common. Juveniles groomed and played with their mothers, but social play with other individuals was almost non-existent. The population comprised two discrete units, or mobs, which were usually broken into subgroups of varying composition and size. In a mob with twenty to twenty-five members, the largest subgroup seen was fifteen; the average size was 3·7 animals. Pairs were more frequent than single animals, indicating a gregarious tendency rare among macropods. Previous authors have probably under-estimated the social structure because they could not repeatedly recognize individuals.

Honey bees, Apis mellifera L., are polyandrous and several males simultaneously father offspring within a single colony. The relatedness of female colony members therefore varies with their paternity: workers encounter both patrilineal full sister (r¯=0·75) and non-patrilineal half-sister (r¯=0·25) nestmates. The impact of this intra-colony genetic variation on social grooming and trophallaxis (liquid food exchange) among workers in colonies consisting of two phenotypically-distinct worker patrilines was examined. Workers in these colonies groomed and fed a disproportionately large number of full sisters despite a tendency to encounter a disproportionately large number of half-sisters. Thus, workers actively discriminated between full and half-sisters. This patrilineal discrimination occurred both in colonies with laying queens and in a queenless colony rearing replacement queens. These results suggest that intracolony genetic variation may have a major effect on colony social organization.

Male behaviour patterns, including ultrasonics, olfactory investigation, grooming and sequences of following of oestrous females during the pre-copulatory period, were described for the Mongolian gerbil. Differences in dependence of these patterns on gonadal hormones were examined by measuring the rates of decline after castration and the degree of restoration following the subcutaneous injection of testosterone propionate (20 μg/2 days/animal). Castration and androgen therapy did not influence the performance of male genital grooming, allogrooming and the olfactory investigation of both female secretory products and the female's body, excluding the posterio-dorsal area. The other male patterns differed in the extent to which they were affected. Thus ventral gland marking, foot-stomping and sequences of follow/dart interactions declined rapidly and were not restored to pre-castration levels by androgen; whereas the upsweep ultrasonic vocalization and olfactory investigation of the female's perineal area declined more gradually, and were completely restored. These consistent differences in both decline and restoration suggest that mechanisms underlying some pre-copulatory patterns are influenced by androgen to a greater degree than others.