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iOS App (for iPhone & iPod Touch) that provides a professional-level solution to the logging of animal (including human) behaviour, implementing discipline-standard protocols in a highly flexible structure that will useable across a range of species.

Infanticide is well documented in chimpanzees and various hypotheses have been proposed to explain this behavior. However, since infanticide by chimpanzees is relatively rare, it has thus far not been possible to thoroughly test these hypotheses. Here we present an analysis of the largest dataset of infanticides from a single community of chimpanzees, a full record of all intra- community infanticides and failed attempts at infanticide over a 24-year period for the Sonso community of chimpanzees in the Budongo Forest, Uganda. We use these data to test four hypotheses for this behavior: the sexual selection hypothesis, male mating competition, resource competition, and meat acquisition. Our dataset consisted of 33 attacks on 30 victims, 11 of which were ‘definite’ infanticides, four of which ‘almost certain’, and nine were ‘suspected’, while nine were ‘attempted’ infanticides. The majority of attacks where the perpetrators were known (23) had only male attackers and victims were disproportionately young (two-thirds of victims with known ages were under 1 week old). Our data best support the sexual selection hypothesis for infanticide. Cannibalism was infrequent and partial, suggesting meat acquisition was a by-product of infanticide, and there was no evidence to suggest that infanticide was part of a male strategy to eliminate future competi- tors. Infanticide by females was rare, but we suggest sexual selection, operating through intra-sexual competition, may also be responsible for infanticide by females.

Objectives: Infanticide by males is common in mammals. According to the sexual selection hypothesis, the risk is inversely related to infant age because the older the infant, the less infan- ticide can shorten lactational amenorrhea; risk is also predicted to increase when an infanticidal male's chance of siring the replacement infant is high. Infanticide occurs in chimpanzees (Pan troglodytes), a species in which male dominance rank predicts paternity skew. Infanticidal male chimpanzees (if low-ranking) are unlikely to kill their own offspring, whereas those who are cur- rently rising in rank, particularly when this rise is dramatic, have an increased likelihood of fathering potential future infants relative to any existing ones. Given that mothers should behave in ways that reduce infanticide risk, we predicted that female chimpanzees, and specifi- cally those with younger, more vulnerable infants, would attempt to adjust the exposure of their infants to potentially infanticidal males. Specifically, mothers of young infants should reduce their association with adult males in general, and to a greater extent, with both low-ranking males and those rising in rank from a position where paternity of current infants was unlikely, to a rank where the probability of siring the next infant is significantly higher. We also investigated the alternative possibility that rather than avoiding all adult males, mothers would increase association with males of stable high rank on the basis that such males could offer protection against infanticide. Materials and methods: We examined data on female association patterns collected from the Budongo Forest, Uganda, during a period encompassing both relative stability in the male hierar- chy and a period of instability with a mid-ranking male rising rapidly in rank. Results: Using linear mixed models, we found that mothers reduced their association with the rank-rising male, contingent on infant age, during the period of instability. We

Infanticide by males is common in mammals. According to the sexually-selected infanticide hypothesis, risks increase when males can kill unrelated infants, and when an infanticidal male’s chance of siring the replacement infant is high. Infanticide occurs in chimpanzees (Pan troglodytes), and rank predicts paternity, so infanticidal low-ranking males are unlikely kill their own offspring while males who rise in rank are more likely to father potential future infants than any existing ones. Given that mothers should be selected to reduce infanticide risk, we predicted that they would attempt to adjust the exposure of their infants to potentially-infanticidal males: specifically, that they would reduce association with low-ranking and rank-rising males. We examined data on female association patterns collected from the Budongo Forest, Uganda, during a period encompassing both relative stability in the male hierarchy and a period of instability with a mid-ranking male rising rapidly in rank. Using linear mixed models, we found that mothers reduced their association with mid-low ranking males, and particularly with the rank-rising male, contingent on infant age, during the period of instability. Our results support the sexually-selected hypothesis for infanticide, and demonstrate that female chimpanzees are sensitive to the relative risks posed by adult males.

The evolution of cooperation remains a central issue in socio-biology with the fundamental problem of how individuals minimize the risks of being short-changed (‘cheated’) should their behavioural investment in another not be returned. Economic decisions that individuals make during interactions may depend upon the presence of potential partners nearby, which o ers co operators a temptation to defect from the current partner. The parcelling model posits that donors subdivide services into parcels to force cooperation, and that this is contingent on opportunities for defection; that is, the presence of bystanders. Here we test this model and the e ect of bystander presence using grooming interactions of wild chimpanzees. We found that with more bystanders, initiators gave less grooming at the beginning of the bout and were more likely to abandon a grooming bout, while bouts were less likely to be reciprocated. We also found that the groomer’s initial investment was not higher among frequent groomers or stronger reciprocators, suggesting that contrary to current assumptions, grooming decisions are not based on trust, or bonds, within dyads. Our work highlights the importance of considering immediate social context and the in uence of bystanders for understanding the evolution of the behavioural strategies that produce cooperation.

Infanticide by males is common in mammals. According to the sexually-selected infanticide hypothesis, risks increase when males can kill unrelated infants, and when an infanticidal male’s chance of siring the replacement infant is high. Infanticide occurs in chimpanzees, and rank predicts paternity, so infanticidal low-ranking males are unlikely kill their own offspring while males who rise in rank are more likely to father potential future infants than any existing ones. Given that mothers should be selected to reduce infanticide risk, we predicted that they would attempt to adjust the exposure of their infants to potentially-infanticide males: specifically, that they would reduce association with low-ranking and rank-rising males. We examined data on female association patterns collected from the Budongo Forest, Uganda, during a period encompassing both relative stability in the male hierarchy and a period of instability with a mid-ranking male rising rapidly in rank. We found that in the period of instability, mothers with younger infants reduced their association with mid-low ranking males, and particularly the rank-rising male. Our results support the sexually-selected hypothesis for infanticide, and demonstrate that female chimpanzees are sensitive to the relative risks posed by adult males.

Dunbar’s general model of mating strategies provides a useful, but largely ignored approach for understanding the fundamental choice faced by male: to remain with females in order to exploit paternity opportunities when they arise, a social strategy, or to search for these opportunities on an ongoing, roving, basis. The model has been criticized in both its assumptions, and the data used to test it. Using published data from six different communities of chimpanzees, we address three questions: How robust is Dunbar’s original model; how robust is its support for social males in West and roving males in East Africa; and how real are supposed differences in female gregariousness between West and East African chimpanzees? We test the original model against two variants and find that despite quantitative differences, all three generate the same qualitative prediction. Thus for chimpanzees at least, Dunbar’s original model can be regarded as fairly robust. However, this prediction is that chimpanzee males should pursue a ‘roving’ strategy and that this was as true for West as for East African chimpanzees. Furthermore, the comparative data did not support an East/West dichotomy in female gregariousness. This study highlights the importance of the collection and reporting of comparable data, the utility of simple mathematical models, and the similarities in behaviour across subspecies of chimpanzees.

Comparative approaches are fundamental to behavioral ecology, yet differences in methodology and approach limit opportunities for this when studying chimpanzees. We studied two communities, the Sonso community of the Budongo Forest, Uganda, and M-group of the Mahale Mountains National Park, Tanzania using a common set of definitions and protocols focusing on male social interactions. We found striking differences between the two communities. Sonso males were similar to those in other East African communities, showing evidence of effective aggressive coercion of females, the provision of agonistic support and the trading of grooming for rank-restricted commodities. By contrast M-group males were ineffective in their use of aggression to coerce females, and neither seemed to provide nor trade for commodities such as agonistic support or social tolerance. Placing our data in a comparative context, we identified variation in structural despotism and in both membership and age profiles of adult male cliques. In our samples, Sonso males showed a high level of structural despotism while the M-group male fell at the opposite end of the cross-community distribution, being more structurally egalitarian. We discuss how demography, through aggressive interactions and structural despotism, impacts male social behavior (including both grooming & mating strategies). Our findings also highlight how the degree of structural despotism in a community is labile and not a species-specific characteristic.

Across taxa, males employ a variety of mating strategies, including sexual coercion and the provision, or trading, of resources. Biological Market theory (BMT) predicts that trading of commodities for mating opportunities should exist only when males cannot monopolise access to females and/or obtain mating by force, in situations where power differentials between males are low; both coercion and trading have been reported for chimpanzees (Pan troglodytes). Here, we investigate whether the choice of strategy depends on the variation in male power differentials, using data from two wild communities of East African chimpanzees (P.t. schweinfurthii): the structurally despotic Sonso community (Budongo, Uganda) and the structurally egalitarian M-group (Mahale, Tanzania). We found evidence of sexual coercion by male Sonso chimpanzees, and of trading—of grooming for mating—by M-group males; females traded sex for neither meat nor protection from male aggression. Our results suggest that the despotism–egalitarian axis influences strategy choice: male chimpanzees appear to pursue sexual coercion when power differentials are large and trading when power differentials are small and coercion consequently ineffective. Our findings demonstrate that trading and coercive strategies are not restricted to particular chimpanzee subspecies; instead, their occurrence is consistent with BMT predictions. Our study raises interesting, and as yet unanswered, questions regarding female chimpanzees’ willingness to trade sex for grooming, if doing so represents a compromise to their fundamentally promiscuous mating strategy. It highlights the importance of within-species cross-group comparisons and the need for further study of the relationship between mating strategy and dominance steepness.

Chimpanzees of the Sonso community, Budongo Forest, Uganda were observed eating clay and drinking clay-water from waterholes. We show that clay, clay-rich water, and clay obtained with leaf sponges, provide a range of minerals in different concentrations. The presence of aluminium in the clay consumed indicates that it takes the form of kaolinite. We discuss the contribution of clay geophagy to the mineral intake of the Sonso chimpanzees and show that clay eaten using leaf sponges is particularly rich in minerals. We show that termite mound soil, also regularly consumed, is rich in minerals. We discuss the frequency of clay and termite soil geophagy in the context of the disappearance from Budongo Forest of a formerly rich source of minerals, the decaying pith of Raphia farinifera palms.

Biological-markets theory models the action of natural selection as a marketplace in which animals are viewed as traders with commodities to offer and exchange. Studies of female Old World monkeys have suggested that grooming might be employed as a commodity to be reciprocated or traded for alternative services, yet previous tests of this grooming-trade model in wild adult male chimpanzees (Pan troglodytes) have yielded mixed results. Here we provide the strongest test of the model to date for male chimpanzees: we use data drawn from two social groups (communities) of chimpanzees from different populations, and give explicit consideration to variation in dominance hierarchy steepness as such variation results in differing conditions for biological markets. First, analysis of data from published accounts of other chimpanzee communities, together with our own data, showed that hierarchy steepness varied considerably within and across communities and that the number of adult males in a community aged 20-30 years predicted hierarchy steepness. The two communities in which we tested predictions of the grooming-trade model lay at opposite extremes of this distribution. Second, in accord with the grooming-trade model, we found evidence that male chimpanzees trade grooming for agonistic support where hierarchies are steep (despotic) and consequent effective support is a rank-related commodity, but not where hierarchies are shallow (egalitarian). However, we also found that grooming was reciprocated regardless of hierarchy steepness. Our findings also hint at the possibility of agonistic competition, or at least exclusion, in relation to grooming opportunities compromising the free market envisioned by Biological Markets theory. Our results build on previous findings across chimpanzee communities to emphasise the importance of reciprocal grooming exchanges among adult male chimpanzees, which can be understood in a biological markets framework if grooming by or with particula

Chimpanzees (Pan troglodytes) are capable of extreme violence. They engage in inter?group, sometimes lethal, aggression that provides the winners with an opportunity to enlarge their territory, increase their food supply and, potentially, attract more mates. Lethal violence between adult males also occurs within groups but this is rare; to date, only four cases (three observed and one inferred) have been recorded despite decades of observation. In consequence, the reasons for within?group lethal violence in chimpanzees remain unclear. Such aggression may be rare due to the importance of coalitions between males during inter?group encounters; cooperation between males is also thought to be key in the defense or advancement of social rank within the group. Previous accounts of within?group lethal violence concern victims who were low?ranking males; here we provide the first account of the killing of an incumbent alpha male by a coalition of adult males from the same community. We found no clear evidence that the alpha male’s position was under threat during the months before the lethal attack: the male dominance hierarchy was highly stable, with low rates of male–male aggression, and there were no significant changes in social interactions (i.e. grooming and aggression) between the alpha male and the other adult males. Two of the four attackers were former alpha males and were the individuals with whom the victim appeared, in the period preceding his death, to be most strongly affiliated: his most frequent grooming partners and those with whom he spent most time in proximity. The lethal attack triggered a period of instability in the male hierarchy and was likely an opportunistic attempt to seize alpha status by the third?ranking male.

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 im- mediate 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.

The attribution of culture to non-human animals has been controversial and continues to fuel much heated debate, much of which hinges on how culture is defined. We illustrate how definitions have become less human-centric as observations from wild primates have led to a new discipline – cultural primatology – and challenged the idea of culture as uniquely human. Although cultural primatology has it roots in field studies of wild primates, the weight of captive studies across a variety of species has resulted in a comparative view of culture which emphasises the mechanism of transmission. We argue that, while this has broadened the species and behaviours that have been considered ‘cultural’, it weakens the usefulness of comparative studies in understanding the evolutionary origins of human culture. We prefer a definition that centres on the concept of culture as an array of behaviour patterns across multiple domains that vary between groups or populations due to differing histories of social transmission. We argue for the necessity of field studies of wild primates in the comparative study of culture, providing examples of how such studies allow both the identification of cultures across non-human primate social groups and the mechanisms by which behaviours are transmitted both within and between groups. Such studies are essential for an ecologically valid understanding of culture, and to investigate how social dynamics, ecology and demographics shape culture and the diffusion and dissemination of socially learned behaviours.

Perhaps more than for any other human behavior, the evolutionary heritage of violence has been the subject of vigorous debate: whether shared patterns of intra-specific aggression between humans and other species doom us to a bloody existence. This chapter reviews intra-specific aggression and violence among mammalian species, focusing on primates. It highlights three themes: aggression is a part of everyday life for most social animals; the vast majority of conflicts in animal societies are of low intensity; there are extraordinary examples within the broad spectrum of aggressive behaviors seen in nonhumans that conform to even the most anthropocentric definitions of violence. To illustrate the latter, the chapter reviews violence in chimpanzees, the extant species most closely related to humans and which, next to humans, exhibits the most spectacularly gruesome and varied aggressive repertoire in mammals.