Peter Henzi

• University of Lethbridge

We assess the proposition that intergroup conflict (IGC) in non-human primates offers a useful comparison for studies of human IGC and its links to parochial altruism and prosociality. That is, for non-linguistic animals, social network integration and maternal influence promote juvenile engagement in IGC and can serve as the initial grounding for...

The alarm calls of vervet monkeys (Chlorocebus pygerythrus) have been the subject of considerable focus by researchers, owing primarily to the purported referential qualities of different alarm call types. With this focus on reference, acoustic variation among calls elicited by the same range of predators has typically been overlooked. Specifically...

The physiological performance of a mother during reproduction represents a trade‐off between continued investment in her current offspring, and the mother's own survival and ability to invest in future offspring. Here, we used core body temperature (Tb) patterns to examine the degree to which maternal body temperatures support the infant during per...

Understanding the development of social relationships can provide insights into the processes by which social network structures emerge and vary across species. Here we extend a previous analysis (Vilette et al., 2022, Animal Behaviour, 194, 205–223) that tested Kohn's (2019, Animal Behaviour, 154, 1–6) model of social relationship formation in thr...

We present data on life history parameters from a long-term study of vervet monkeys in the Eastern Cape, South Africa. Estimates are presented of age at first conception for females and age at natal dispersal for males, along with the probability of survival to adulthood for infants born during the study, female reproductive life-span, reproductive...

Consistent inter-individual differences in behaviour are thought to be related to consistency in social network position. There is also evidence that network structures can show predictable temporal dynamics, suggesting that consistency in social network position across time does not preclude some form of plasticity in response to environmental var...

Understanding the development of social relationships, or the process of socialization, can provide insights into the processes by which social network structures emerge and vary across species. In this analysis, we investigated the process of network formation from a developmental perspective using data from three groups of wild vervet monkeys, Ch...

Animals often differ in their responses towards novelty, and sometimes these differences are consistent across individuals. Here, we explored interindividual variation in neophilia towards novel foods by recording whether animals ingested novel food stuffs (Nindividuals = 116; Ntrials = 276) in three troops of wild vervet monkeys. We tested for the...

Social animals frequently show dynamic social network patterns, the consequences of which are felt at the individual and group level. It is often difficult, however, to identify what drivers are responsible for changes in these networks. We suggest that patterns of network synchronization across multiple social groups can be used to better understa...

Most primates, including humans, give birth during the inactive phase of the daily cycle. Practical constraints therefore limit our knowledge of the precise timing of nocturnal birth in wild diurnal primates and so limit our understanding of selective pressures and consequences. We measured maternal core body temperature (Tb) across 24 births in a...

The anthropoid primates are known for their intense sociality and large brain size. The idea that these might be causally related has given rise to a large body of work testing the ‘social brain hypothesis'. Here, the emphasis has been placed on the political demands of social life, and the cognitive skills that would enable animals to track the ma...

Although sickness behaviour in response to non-lethal parasites has been documented in wild animals, it remains unclear how social and environmental stress might also shape an animal’s behavioural response to parasitism, nor do we know whether simultaneous infection with more than one parasite changes the way animals respond. Here, we combine physi...

Significance Using state-of-the-art biologging technology, we document the occurrence of fevers in wild vervet monkeys and demonstrate that fevers coincide with overt sickness behavior. In so doing, we demonstrate a hidden cost of sociality: Febrile animals were twice as likely to receive aggression from their group mates and were six times more li...

Strategies that mitigate predation, whether proactive or reactive, can nevertheless impose significant ‘nonconsumptive’ costs on prey species. Here we used data from two wild vervet monkey, Chlorocebus pygerythru,s groups to assess whether the detection of predators affected their subsequent behaviour to the detriment of their short-term foraging e...

Although sickness behaviour in response to non-lethal parasites has been documented in wild animals, it remains unclear how social and environmental stress might also shape an animal’s behavioural response to parasitism, nor do we know whether simultaneous infection with more than one parasite changes the way animals respond. Here, we combine physi...

Parasite and pathogen incidence and prevalence is driven by both periodic variation in environmental conditions and host characteristics. Given the increasing risk of zoonotic transmission to humans, and the close phylogenetic relationship between humans and non‐human primates, understanding this variation in parasite dynamics is becoming essential...

Muzzle contact, where one animal brings its muzzle into close proximity to that of another, has often been hypothesized as a straightforward means of socially mediated food investigation. Using 2,707 observations of muzzle contact occurring across 3 troops of wild vervet monkeys (Chlorocebus pygerythrus), we tested this social learning hypothesis....

In the face of climate change there is an urgent need to understand how animal performance is affected by environmental conditions. Biophysical models that use principles of heat and mass transfer can be used to explore how an animal's morphology, physiology, and behavior interact with its environment in terms of energy, mass and water balances to...

The development of numerical methods for inferring social ranks has resulted in an overwhelming array of options to choose from. Previous work has established the validity of these methods through the use of simulated datasets, by determining whether a given ranking method can accurately reproduce the dominance hierarchy known to exist in the data....

Understanding the physiological processes that underpin primate performance is key if we are to assess how a primate might respond when navigating new and changing environments. Given the connection between a mammal's ability to thermoregulate and the changing demands of its thermal environment, increasing attention is being devoted to the study of...

Understanding the physiological processes that underpin primate performance is key if we are to assess how a primate might respond when navigating new and changing environments. Given the connection between an animal’s ability to thermoregulate and the changing demands of its thermal environment, increasing attention is being devoted to the study o...

The development of multi-layer network techniques is a boon for researchers who wish to understand how different interaction layers might influence each other, and how these in turn might influence group dynamics. Here, we investigate how integration between male and female grooming and aggression interaction networks influences male power trajecto...

Learning is valuable because it allows animals to vary behavior in response to lifetime environmental changes. Variation in behavior is often associated with variation in learning abilities, especially social learning abilities, and such variation is generally viewed as species-typical. However, new evidence is revealing the importance of consideri...

In the animal kingdom, conspicuous colors are often used for inter- and intra-sexual communication. Even though primates are the most colorful mammalian taxon, many questions, including what potential information color signals communicate to social partners, are not fully understood. Vervet monkeys (Chlorocebus pygerythrus) are ideal to examine the...

As the effects of global climate change become more apparent, animal species will become increasingly affected by extreme climate and its effect on the environment. There is a pressing need to understand animal physiological and behavioural responses to climatic stressors. We used the reactive scope model as a framework to investigate the influence...

The function of many animal behaviors seem straight forward, but sometimes straight-forward behaviors function in more complex ways. Here we explored muzzle contact, a behavior seen in many species, that until now has been presented as a rather straight-forward means to investigate food by sniffing the mouths of others. By analyzing 2,707 instances...

Infant vervet monkeys are born completely dependent on their mothers for their energetic intake. Thus, we hypothesized that maternal attributes, such as parity and rank, would play a role in infant survivability to weaning age. Additionally, we predicted that the year they were born in would also play a large role in infant survivability due to hig...

Given a changing climate and large-scale human migration, understanding infectious diseases in wildlife and the factors that drive the spread of these diseases is becoming increasingly important. Owing to the close phylogenetic relationship between nonhuman primates and humans, primate parasites are of particular interest due to the potential for z...

Males in female-philopatric social groupings leave their natal groups to pursue successive reproductive opportunities in one or more other groups. In vervet monkeys, Chlorocebus pygerythrus, adult males coexist and physical eviction is not a driver of male movement. Migratory decisions are expected to turn on an evaluation of future reproductive op...

Recent studies have highlighted the link between consistent inter-individual differences in behaviour and consistency in social network position. There is also evidence that network structures can show temporal dynamics, suggesting that consistency in social network position across time does not preclude some form of plasticity in response to envir...

The importance of social hierarchies has led to the development of many techniques for inferring social ranks, leaving researchers with an overwhelming array of options to choose from. Many of our research questions involve longitudinal analyses, so we were interested in a method that would provide reliable ranks across time. But how does one deter...

Animals are thought to acquire, apply, and exploit information in order to exhibit socially-learned behavior. In chacma baboons (Papio ursinus), Carter et al. (2016) suggested that it is possible to explain variation in a novel, socially-learned behavior by identifying phenotypic constraints (cognitive, social, behavioral, ecological, and demograph...

Male reproductive strategies have been well studied in primate species where the ability of males to monopolize reproductive access is high. Less is known about species where males cannot monopolize mating access. Vervet monkeys (Chlorocebus pygerythrus) are interesting in this regard as female codominance reduces the potential for male monopolizat...

We explored whether emotion understanding promotes positive social functioning in childhood using the Ability Emotional intelligence (AEI) framework, which defines emotion understanding more broadly than is common in developmental science. The prospective study included children ages 9 to 11 years who completed a measure of AEI at the start of the...

Vervet monkeys (Chlorocebus pygerythrus) engage frequently in muzzle contact, where one individual (the initiator) brings its muzzle into close proximity to the muzzle of a conspecific (the receiver). Muzzle contacts occur daily among vervet monkeys and persist throughout the lifespan. Early research hypothesized that muzzle contacts promoted socia...

Current climate change predictions show that primate habitats are expected to experience 10% more warming than the global mean (Graham et al., 2016). Recent droughts in South Africa have been reported as the driest since record keeping started in 1904 (Joubert, 2016). These drying conditions are predicted to cause a general global contraction of fo...

Variation within and across populations is a necessary component of natural selection, and within-subject variation is a necessary component of behavioral selection. In the animal behavior literature, “boldness” is a measure of the propensity of animals to approach novel stimuli. Boldness is considered to be a measure of animal behavior “personalit...

Social networks can be adaptive for members and a recent model (Ilany and Akçay 2016 Nat. Comm.7, 12084 (doi:10.1038/ncomms12084)) has demonstrated that network structure can be maintained by a simple process of social inheritance. Here, we ask how juvenile vervet monkeys integrate into their adult grooming networks, using the model to test whether...

In mobile social groups, cohesion is thought to be driven by patterns of attraction at both the individual and group level. In long-lived species with high group stability and repeated interactions, such as baboons, individual-to-individual attractions have the potential to play a large role in group cohesion and overall movement patterns. In previ...

Studies across a range of species have shown that sociability has positive fitness consequences. Among baboons, both increased infant survival and adult longevity have been associated with the maintenance of strong, equitable and durable social bonds. However, not all baboon populations show these patterns of bonding. South African chacma baboons (...

In mobile social groups, influence patterns driving group movement can vary between democratic and despotic. The arrival at any single pattern of influence is thought to be underpinned by both environmental factors and group composition. To identify the specific patterns of influence driving travel decision-making in a chacma baboon troop, we used...

While most primates are tropical animals, a number of species experience markedly cold winters. In a high latitude arid environment, wild female vervet monkeys (Chlorocebus pygerythrus) that are socially integrated experience reduced cold stress. Here we ask whether sociability is similarly salient for male vervet monkeys, who reside in non-natal g...

Sexual conflict theory expects females to avoid non-optimal mating attempts by males. Although female vervet monkeys can resist direct mating attempts, higher-ranking males still have more mating opportunities than lower-ranking ones. We presume that rank-related access reflects male-male competition that may conflict with female reproductive objec...

In mobile social groups, influence patterns driving group movement can vary between democratic and despotic. The arrival at any single pattern of influence is thought to be underpinned by environmental factors and group composition. To determine the specific patterns of influence in a chacma baboon troop we used spatially explicit data to identify...

In mobile social groups, influence patterns driving group movement can vary between democratic and despotic. The arrival at any single pattern of influence is thought to be underpinned by environmental factors and group composition. To determine the specific patterns of influence in a chacma baboon troop we used spatially explicit data to identify...

It is generally assumed that high-resolution movement data are needed to extract meaningful decision-making patterns of animals on the move. Here we propose a modified version of force matching (referred to here as direction matching), whereby sparse movement data (i.e., collected over minutes instead of seconds) can be used to test hypothesized fo...

The spatial configuration of a group of animals should reflect the ability of its members to respond to environmental contingencies. Under predation risk, the optimal position for an individual in a stationary group is at the group's centre. The resulting group geometry is circular, with individual placement determined by competitive ability. Where...

Understanding how vervet monkeys (Chlorocebus pygerythrus) select resources provides information for effectively managing them and the environments they live in, which may reduce conflict with humans. This study investigates resource selection on woody plant species by two vervet monkey (vervet) troops living in human-modified mixed-broadleaf savan...

Reduction of predation risk represents the most likely explanation for the evolution of group-living among the anthropoid primates. Obligate sociality leads to increased competition for resources, meaning that animals may face a trade-off between safe positions within the troop and increased foraging efficiency. Dominance has been proposed to be a...

Unrelated male primates frequently cohabit in bisexual groups and, despite being reproductive competitors, have been shown to cooperate in ways that are associated with reproductive success. Such coalitions between males are common in some taxa, where they can serve two primary functions – status management and improved mating opportunities – that...

A strong case has been made that the primary function of grooming is hygienic. Nevertheless, its persistence in the absence of hygienic demand, and its obvious tactical importance to members of primate groups, underpins the view that grooming has become uncoupled from its utilitarian objectives and is now principally of social benefit. We identify...

The current study investigated the association between Machiavellianism and children’s peer interactions in the playground using observational methods. Primary school children (N = 34; 17 female), aged 9 to 11 years, completed the Kiddie Mach scale and were observed in natural play during 39 recesses (average observed time = 11.70 hours) over a ful...

Field data often include multiple observations taken from the same individual. In order to avoid pseudoreplication, it is commonplace to aggregate data, generating a mean score per individual, and then using these aggregated data in subsequent analyses. Aggregation, however, can generate problems of its own. Not only does it lead to a loss of infor...

Sociality has been shown to have adaptive value for gregarious species, with more socially integrated animals within groups experiencing higher reproductive success and longevity. The value of social integration is often suggested to derive from an improved ability to deal with social stress within a group; other potential stressors have received l...

The extent to which animal vocalizations convey specific information about events in the environment is subject to continued debate. The alarm-calls of vervet monkeys have played a pivotal role in this debate as they represent the classic example of a predator-specific call production system combined with a set of equally specific responses by rece...

We used two sets of videotaped data of playing domestic dog dyads to determine whether rolling over during play served as a signal of submission or whether it was a combat manouevre adopted as part of an ongoing play sequence. Our results provide strong support for the latter. In the absence of any overt indication of agonism, the frequency with wh...

INTRODUCTION: The use of parallel lasers for the measurement of morphological traits in field conditions, where two independent lasers at a fixed distance are projected onto a surface and then recorded via photogrammetry for actual measurement, was pioneered by Bergeron (2007), then later improved on by Rothman et al (2008). One drawback of current...

Responses to environmental variability sheds light on how individuals are able to survive in a particular habitat and provides an indication of the scope and limits of its niche. To understand whether climate has a direct impact on activity, and determine whether vervet monkeys have the behavioral flexibility to respond to environmental change, we...

We used implanted miniature data loggers to obtain the first measurements of body temperature from a free-ranging anthropoid primate. Vervet monkeys (Chlorocebus pygerythrus) living in a highly seasonal, semi-arid environment maintained a lower mean 24-h body temperature in winter (34.6 ± 0.5 °C) than in summer (36.2 ± 0.1 °C), and demonstrated inc...

During play fighting, animals make a variety of movements, some of which seem unrelated to the ongoing actions of the partner. Among such movements are the jumps and rotations reported in many species of Old World monkeys. In the present study, videotaped sequences of jumps and rotations performed by juvenile vervet monkeys were analyzed. Using the...

One hundred and forty-nine 8-11 year-old children (86 males; M = 9 years - 4 months and SD = 7 months) from the UK were administered the Trust Beliefs in Peers scale and were observed in the playground over one school year. Quadratic relations were found between trust beliefs in peers and peer interaction, which varied by gender. Compared to girls...

We suggest a methodology for analyzing movement behaviors of individuals moving in a group. Group movement is analyzed at two levels of granularity: the group as a whole and the individuals it comprises. For analyzing the relative positions and movements of the individuals with respect to the rest of the group, we apply space transformation, in whi...

Large-scale interspecific studies of mammals ranging between 0.04-280 kg have shown that larger animals walk with more extended limb joints. Within a taxon or clade, however, the relationship between body size and joint posture is less straightforward. Factors that may affect the lack of congruence between broad and narrow phylogenetic analyses of...

Primate social life and behaviour is contingent on a number of levels: phylogenetic, functional and proximate. Although this contingency is recognized by socioecological theory, variability in behaviour is still commonly viewed as 'noise' around a central tendency, rather than as a source of information. An alternative view is that selection has ac...

Free-ranging vervet monkeys can solve a complex, multi-player coordination problem, learning to remain outside a 'forbidden circle' imposed by one member of the troop, in the absence of any social learning, communication, or policing by more dominant animals.

Highlights ► Assessment of monthly and hourly activity patterns in wild vervet monkeys. ► Scan sampling and biologging provide comparable measures of monthly activity. ► Scan sampling and biologging provide comparable measures of hourly activity. ► Validation of biologger methods in their measurement of activity.

Narrow riparian woodlands along non-perennial streams have made it possible for vervet monkeys to penetrate the semi-arid karoo ecosystem of South Africa, whilst artificial water points have more recently allowed these populations to colonize much more marginal habitat away from natural water sources. In order to better understand the sequelae of l...

The hypothesis that lonely children show hypervigilance for social threat was examined in a series of three studies that employed different methods including advanced eye-tracking technology. Hypervigilance for social threat was operationalized as hostility to ambiguously motivated social exclusion in a variation of the hostile attribution paradigm...

Understanding human cognitive evolution, and that of the other primates, means taking sociality very seriously. For humans, this requires the recognition of the sociocultural and historical means by which human minds and selves are constructed, and how this gives rise to the reflexivity and ability to respond to novelty that characterize our specie...

The idea that female mammals can manipulate the duration of each other's estrus in an effort to influence the degree of synchrony between their periods of sexual receptivity is a persistent and popularly held one. It is frequently cited as proof of pheromonal communication in humans and often invoked by models of female reproductive strategies more...

We used data from two troops of free-ranging vervet monkeys (Chlorocebus aethiops) to assess the proposition that the conspicuous chest rubbing observed in this species constitutes scent-marking behavior. Our data indicate that chest-rubbing behavior is associated with higher-ranking males who are more likely to do so during the breeding season in...

Primates living outside protected areas frequently come into conflict with humans. While the focus of most research has been on the costs and consequences of crop raiding in relation to subsistence agriculture, large-scale commercial agriculture presents conservation challenges of its own. Baboons that occupy commercial pine plantations in southern...

Individuals interact with conspecifics in a number of behavioural contexts or dimensions. Here, we formalise this by considering a social network between n individuals interacting in b behavioural dimensions as a nxnxb multidimensional object. In addition, we propose that the topology of this object is driven by individual needs to reduce uncertain...

Contrary to the expectations of biological market theory, in species where sexual coercion is effective males often exchange resources or services with females for the opportunity to mate. This suggests that an ability to control mating partners does not preclude the need for their cooperation. We argue that this is because, in many systems, female...

Vervet monkeys (Chlorocebus aethiops) are African cercopithecines whose wide distribution is a consequence of their ability to penetrate semi-arid environments, but whose territoriality is assumed to limit their ability to respond to water shortage. Data from a population in the South African karoo semi-desert during a drought year indicate not onl...

Alpha male chacma baboons experience uncontested access to individual estrus females. Consequently, alpha male paternity certainty is high and underpins significant levels of infanticide by immigrant males that, in turn, has selected for male defense of infants. There is also, however, a high probability that alpha males will be absent during the...

Previous studies on facial recognition have considered widely separated populations, both geographically and culturally, making it hard to disentangle effects of familiarity with an ability to identify ethnic groups per se. We used data from a highly intermixed population of African peoples from South Africa to test whether individuals from nine di...

The plant communities occurring in the home ranges of two vervet monkey (Chlorocebus aethiops) troops (referred to as the Donga and Picnic troops) were investigated as part of a comprehensive research project on the spatial and temporal patterns in resource dispersion or distribution and range use. From two-way indicator species analysis (TWINSPAN)...

Why are humans so clever? The ‘Social intelligence’ hypothesis explores the idea that this cleverness has evolved through the increasing complexity of social groups. Our ability to understand and control nature is a by-product of our ability to understand the mental states of others and to use this knowledge to co-operate or deceive. These abilitie...

We observed 10 breeding pairs within a subcolony of Herring Gulls to ascertain the frequency of intrusion by non-resident gulls, the reasons for these intrusions, and the nature of the responses to them by the territory holders. Most observations were made during the post-hatch phase in order to determine how intrusion might affect chick rearing st...

The probability of ovulation in a number of primate species is associated with both visual and auditory cues. We use 18-month behavioral data from two chacma baboon troops to provide the first systematic assessment of the possibility that olfactory cues are also involved. Using variance in the rate of olfactory inspection by males as a proxy for ch...

We argue that, in the absence of an infanticidal threat from resident males, female chacma baboons favour polyandry because it may predispose multiple males to protect their infants from infanticide by immigrant males. This assumes that the most likely sire, or principal protector, of an infant may often be absent during its period of vulnerability...

There is an established and very influential view that primate societies have identifiable, persistent social organizations. It assumes that association patterns reflect long-term strategic interests that are not qualitatively perturbed by short-term environmental variability. We used data from two baboon troops in markedly different habitats over...

Nineteen scientists from different disciplines collaborated in highlighting new methodological and theoretical aspects in the re-emerging study area of fission-fusion dynamics. The renewed interest in this area is due to the recognition that such dynamics may create unique challenges for social interaction and distinctive selective pressures acting...

Historically, intertroop movement by males in female-philopatric species has been investigated without any consideration of the potential for variance in the competitive ability of males. This is despite the fact that in many species, particularly among the primates, males tend to move multiple times between groups and often vary substantially in t...