Free-ranging Vervet Monkeys Research Articles

Gastrointestinal parasites of vervet monkeys around Lake Hawassa recreational sites, southern Ethiopia

Vervet monkeys (Chlorocebus pygerythrus) are non-human primates belonging to the family Cercopithecidae, which are native to Africa. The objective of the present study was to assess the occurrence of gastrointestinal parasites in free-ranging vervet monkeys. A total of 140 free-ranging vervet monkeys found in the recreational areas of Hawassa city, Ethiopia, were examined for gastrointestinal parasitic infection from November 2013 to April 2014. For the identification of eggs and larvae of nematodes and cysts, oocysts and trophozoites of protozoa, faecal samples were subjected to direct smear and floatation techniques. Overall, out of 140 faecal samples examined, 75 % were found to harbour one or more gastrointestinal nematode parasites. The most frequently detected nematode parasite was hookworms (45.7 %). Parasite eggs suggestive of cestode parasites were found in 7.9 % of the samples. Coccidia were the most commonly detected protozoa parasites (27.1 %). Mixed infections with two or more parasites were detected in 74.3 % of the examined faecal samples. The present study can give baseline information on the occurrence of parasitic infection in wild vervet monkeys in the area. Future studies in the area should focus not only on the animals but also on the determination of the possible transmission of the parasites to humans which do have close interaction with the vervet monkeys.

Using the stable carbon and nitrogen isotope compositions of vervet monkeys (Chlorocebus pygerythrus) to examine questions in ethnoprimatology.

This study seeks to understand how humans impact the dietary patterns of eight free-ranging vervet monkey (Chlorocebus pygerythrus) groups in South Africa using stable isotope analysis. Vervets are omnivores that exploit a wide range of habitats including those that have been anthropogenically-disturbed. As humans encroach upon nonhuman primate landscapes, human-nonhuman primate interconnections become increasingly common, which has led to the rise of the field of ethnoprimatology. To date, many ethnoprimatological studies have examined human-nonhuman primate associations largely in qualitative terms. By using stable carbon (δ13C) and nitrogen (δ15N) isotope analysis, we use quantitative data to understand the degree to which humans impact vervet monkey dietary patterns. Based on initial behavioral observations we placed the eight groups into three categories of anthropogenic disturbance (low, mid, and high). Using δ13C and δ15N values we estimated the degree to which each group and each anthropogenically-disturbed category was consuming C4 plants (primarily sugar cane, corn, or processed foods incorporating these crops). δ13C values were significantly different between groups and categories of anthropogenic-disturbance. δ15N values were significantly different at the group level. The two vervet groups with the highest consumption of C4 plants inhabited small nature reserves, appeared to interact with humans only sporadically, and were initially placed in the mid level of anthropogenic-disturbance. However, further behavioral observations revealed that the high δ13C values exhibited by these groups were linked to previously unseen raiding of C4 crops. By revealing these cryptic feeding patterns, this study illustrates the utility of stable isotopes analysis for some ethnoprimatological questions.

Responses of vervet monkeys in large troops to terrestrial and aerial predator alarm calls

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 receivers. Here, we revisit the vervet alarm-calling system, and assess the hypothesis that these acoustically distinct calls trigger context- and predator-appropriate behavior. We investigated responses in 2 groups of free-ranging vervet monkeys (Chlorocebus pygerythrus) to both natural encounters with predators and experimental presentations of aerial and terrestrial predator alarm calls. Our results show that the modal natural and experimental response was not to initiate escape behavior, either immediately or in the 10s following an alarm call, but to look at the sound source. When monkeys did take evasive action, contextually inappropriate behavior (i.e., behavior that was not appropriate for evading the specific predator type) was as likely to occur as contextually appropriate behavior. The distance at which calls were heard was negatively correlated with the probability of evasive action. Larger group size, and the greater mean distance at which natural calls were heard, may explain why our animals displayed less predator-appropriate evasion or vigilance than expected. We conclude that the broader social and ecological framework in which calls occur, rather than a simple contextually regular linkage between call types and specific predators, shapes animals’ responses to calls in this species.

Social Coordination: Patience Is a Virtue for Vervet Monkeys

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, orpolicing by more dominant animals.

Third-Party Ranks Knowledge in Wild Vervet Monkeys (Chlorocebus aethiops pygerythrus)

The Machiavellian/Social Intelligence Hypothesis proposes that a complex social environment selected for advanced cognitive abilities in vertebrates. In primates it has been proposed that sophisticated social strategies like obtaining suitable coalition partners are an important component of social intelligence. Knowing the rank relationships between group members is a basic requirement for the efficient use of coalitions and the anticipation of counter-coalitions. Experimental evidence for such knowledge currently exists in only few species. Here, we conducted rank reversal playback experiments on adult females belonging to three different groups of free-ranging vervet monkeys (Chlorocebus aethiops pygerythrus) to test their knowledge of the female hierarchy. Playbacks simulating rank reversals (subordinate aggressing a dominant) induced longer looking times than playbacks simulating a dominant aggressing a subordinate. Vervet monkey females therefore seem to compute the rank relationships between other females. Our results suggest that detailed social knowledge about rank relationships may be widespread in primates and potentially also in other species living in stable groups.

Evidence for scent marking in vervet monkeys?

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 areas where territorial encounters occur. We found no indication that chest rubbing was triggered directly by encounters between troops. We conclude that these data, in conjunction with reports of chest rubbing from other Old World monkeys, are sufficiently suggestive of scent marking to warrant further, directed research and support the suspicion that olfactory cues remain important to catarrhines in a number of domains.

Is passive observation of habituated animals truly passive?

The term “habituated” is sometimes used to imply that animals no longer respond to the presence of a human observer. There is an accumulating body of evidence, however, suggesting that habituated animals that no longer perceive humans as a direct threat nevertheless continue to respond to their presence in other ways. Data were collected from a troop of free-ranging vervet monkeys in the Klein Karoo of South Africa for months 5–12 of their habituation period to determine how self-directed behaviour (SDB) was affected by human presence across time. SDB decreased across the 8 month period, indicating that habituation was ongoing. The human observer’s location in relation to the focal animal had a significant effect on SDB. Furthermore, when the habituation period was divided into an early and a late phase this pattern did not arise until the later habituation period (9–12 months). This evidence suggests that animals continue to respond to human presence as they become habituated, although the observed responses change.

Supply and demand determine the market value of food providers in wild vervet monkeys.

Animals neither negotiate verbally nor conclude binding contracts, but nevertheless regularly exchange goods and services without overt coercion and manage to arrive at agreements over exchange rates. Biological market theory predicts that such exchange rates fluctuate according to the law of supply and demand. Previous studies showed that primates pay more when commodities become scarcer: subordinates groomed dominants longer before being tolerated at food sites in periods of shortage; females groomed mothers longer before obtaining permission to handle their infants when there were fewer newborns and males groomed fertile females longer before obtaining their compliance when fewer such females were present. We further substantiated these results by conducting a 2-step experiment in 2 groups of free-ranging vervet monkeys in the Loskop Dam Nature Reserve, South Africa. We first allowed a single low-ranking female to repeatedly provide food to her entire group by triggering the opening of a container and measured grooming bouts involving this female in the hour after she made the reward available. We then measured the shifts in grooming patterns after we added a second food container that could be opened by another low-ranking female, the second provider. All 4 providers received more grooming, relative to the amount of grooming they provided themselves. As biological market theory predicts, the initial gain of first providers was partially lost again after the introduction of a second provider in both groups. We conclude that grooming was fine-tuned to changes in the value of these females as social partners.

Social Awareness in Monkeys

Tests of self-awareness in nonhuman primates have to date been concerned almost entirely with the recognition of an animal's reflection in a mirror. By contrast, we know much less about non-human primates' perception of their place within a social network, or of their understanding of themselves as individuals with unique sets of social relationships. Here we review evidence that monkeys who fail the mirror test may nonetheless behave as if they recognize themselves as distinct individuals, each of whom occupies a unique place in society and has a specific set of relations with others. A free-ranging vervet monkey, baboon, or macaque recognizes other members of his group as individuals. He also recognizes matrilineal kin groups, linear dominance rank orders, and behaves as if he recognizes his own unique place within them. This sense of “social self” in monkeys, however, is markedly different from self-awareness in humans. Although monkeys may behave in ways that accurately place themselves within a social network, they are unaware of the knowledge that allows them to do so: they do not know what they know, cannot reflect on what they know, and cannot become the object of their own attention.

Social Awareness in Monkeys1

Tests of self-awareness in nonhuman primates have to date been concerned almost entirely with the recognition of an animal's reflection in a mirror. By contrast, we know much less about non-human primates' perception of their place within a social network, or of their understanding of themselves as individuals with unique sets of social relationships. Here we review evidence that monkeys who fail the mirror test may nonetheless behave as if they recognize themselves as distinct individuals, each of whom occupies a unique place in society and has a specific set of relations with others. A free-ranging vervet monkey, baboon, or macaque recognizes other members of his group as individuals. He also recognizes matrilineal kin groups, linear dominance rank orders, and behaves as if he recognizes his own unique place within them. This sense of “social self” in monkeys, however, is markedly different from self-awareness in humans. Although monkeys may behave in ways that accurately place themselves within a social network, they are unaware of the knowledge that allows them to do so: they do not know what they know, cannot reflect on what they know, and cannot become the object of their own attention.

Sex and Status Effects on Primate Volubility: Clues to the Origin of Vocal Languages?

Natural human languages are predominantly vocal. This suggests that, during evolution, speech may have enhanced the efficiency, utility, or flexibility of previous vocal behaviors. If so, there may be parallels between certain aspects of the vocalization patterns of human and nonhuman primates. The literature on humans contains evidence for greater frequency of vocalization, or volubility, between female–female than male–male dyads, and greater volubility among individuals of higher than lower social rank or status. We analyzed two classes of vocalization in free-ranging vervet monkey infants. In both classes, females vocalized significantly more often than males, and high-ranking animals were more voluble than mid- and low-ranking animals. If these findings are confirmed in primates other than vervets, it is conceivable that the voice contributes to the solution of some pan-primate problems, offering clues to the vocal bias in human languages.

Diurnal and seasonal variations in vervet monkeys' activity.

This paper analyzed seasonal and diurnal differences in feeding, locomotion, inactivity, and social grooming of adult and subadult free-ranging vervet monkeys in Natal (38 degrees 35'S and 31 degrees 46'E). Breaking down hourly activity budgets from the perspective of reproductive seasons (birth, premating, and mating seasons) which correspond to environmental conditions in Natal, we obtained several results. First, there were diurnal variations for all the behaviours in all seasons studied, except for inactivity during the mating season when days were shorter and there was greater food shortage and sexual competition. Second, the seasonal influence on the hourly periods of increased activity could not be explained solely by the photoperiod or by the other climatic factors analyzed. Finally, over-all seasonal differences in activity were mainly reflected by the hourly distribution of feeding in the morning and the pattern of inactivity throughout the day. Therefore, rhythms in activity should be understood in terms of adaptation to both climatic constraints and other unrelated metabolic requirements.

Human presence reduces predation in a free-ranging vervet monkey population in Kenya

Human presence reduces predation in a free-ranging vervet monkey population in Kenya

The Patterning of Intervention among Male Bonnet Macaques: Reciprocity, Revenge, and Loyalty

The Patterning of Intervention among Male Bonnet Macaques: Reciprocity, Revenge, and Loyalty

Erratum: Variation in Maternal Responsiveness in Free-Ranging Vervet Monkeys: A Response to Infant Mortality Risk?

Previous articleNext article No AccessErratum: Variation in Maternal Responsiveness in Free-Ranging Vervet Monkeys: A Response to Infant Mortality Risk?PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 132, Number 5Nov., 1988 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/284888 Citations: 1Citations are reported from Crossref Copyright 1988 The University of ChicagoPDF download Crossref reports the following articles citing this article:Julie L. Lockwood, Michael P. Moulton Ecomorphological pattern in Bermuda birds: The influence of competition and implications for nature preserves, Evolutionary Ecology 8, no.11 (Jan 1994): 53–60.https://doi.org/10.1007/BF01237665

Empirical tests of reciprocity theory: Problems in assessment

Observations and experiments designed to test Trivers' (1971) theory of reciprocal altruism face two difficulties. First, in many cases the costs and benefits of behaviors being exchanged cannot be expressed directly in terms of effects on the actors' fitness. This is particularly true when an exchange of cooperative acts involves different types of behavior, such as grooming and alliance formation in non-human primates. Second, in many social groups individuals differ widely in their ability to confer benefits on others. High-ranking animals can, for example, offer greater assistance than low-ranking animals and adults can help offspring more than offspring can help adults. As a result, what appears not to be a reciprocal interaction from the observer's point of view may in fact support Trivers' theory when costs and benefits are calculated from the animals' own perspectives. We discuss these issues with special reference to our own experiments on reciprocal exchanges of grooming and alliance formation in free-ranging vervet monkeys.

Variation in Maternal Responsiveness in Free-Ranging Vervet Monkeys: A Response to Infant Mortality Risk?

A playback experiment was designed to examine whether maternal responsiveness (i.e., an aspect of parental care) to the threat of predation varies as a function of infant mortality risk in free-ranging vervet monkeys. Results show that mothers responded most intensely to the threat of predation before two periods when infant mortality risk was highest. In contrast, control females, who did not have infants during the test periods, showed no difference in responsiveness to the threat of predation. Vervet mothers appear to increase their parental care before periods of high infant mortality in order to increase their offspring's chances of survival.

Assessment of meaning and the detection of unreliable signals by vervet monkeys

Free-ranging vervet monkeys, Cercopithecus aethiops, who had learned to ignore playbacks of one type of call by an unreliable signaller subsequently also ignored playback of an acoustically different call by the same individual if the calls had similar referents. Such transfer did not occur if either the identity of the signaller changed or if the two calls had different referents. After repeatedly being played an intergroup call in the absence of other groups, vervets also ignored an acoustically different intergroup call given by the same individual. The monkeys did not transfer habituation, however, if the new call was given by a different individual. In tests where the referents of two calls were different, the monkeys also failed to transfer habituation across call types. Vervet monkeys who had learned to ignore an unreliable leopard alarm call did not later ignore an eagle alarm call, even when the signaller remained the same. Results suggest that vervets, like humans, process information at a semantic, and not just an acoustic, level.

How Infant Vervet Monkeys Learn To Recognize Starling Alarm Calls: the Role of Experience

Natural observations and field playback experiments were conducted on five groups of free-ranging vervet monkeys to determine when infants recognize the alarm calls of starlings as general alerting signals. Results show that infants do not recognize starling alarm calls at birth. Recognition of starling calls emerges gradually and age at recognition is affected by differences in auditory environment. Infants who have heard starling alarm calls at high rates respond at an earlier age than infants who hear calls at low rates. More importantly, in those groups where infants respond at an earlier age, starlings give alarm calls to vervet predators more often than to non-vervet predators. Thus in the former groups, when adults respond to starling alarm calls, their behavior is more positively reinforcing than in the other groups where starling alarm calls are commonly given to non-vervet predators.

The influence of intergroup competition on the survival and reproduction of female vervet monkeys

Primate groups are often larger than might be predicted from a consideration of within-group competition alone. Wrangham (1980) has hypothesized that females live in extended kin groups in order to defend food resources against other groups. In contrast, others have argued that predation pressure, rather than intergroup competition, favors sociality. Data gathered over 10 years on a population of free-ranging vervet monkeys provide more support for the food defense hypothesis than for the predation hypothesis, and suggest than female reproductive success can be influenced strongly by intergroup competition. 1. Of the three groups under intensive study, the smallest experienced the least predation, arguing against the hypothesis that large groups have evolved as a defense against predation. 2. At least three different measures indicated that larger groups experienced slightly greater infant and juvenile female survival than did smaller groups. 3. Larger groups also had larger and better quality ranges than smaller groups. Large groups were more likely to make incursions into the ranges of smaller groups than vice versa, and to expand their ranges at the expense of smaller groups. Perhaps as a result, females in small groups were more aggressive during intergroup encounters than were females in large groups. 4. Within groups, rank reversals were influenced by the presence of female kin, and individuals with female kin were able to rise in rank over those without kin. There was no evidence that high-ranking females attempted to suppress the recruitment of daughters by low-ranking females, however, perhaps because groups with many females had a competitive advantage over groups with fewer females. 5. Data from a small number of group fusions support the hypothesis that small groups benefit from the recruitment of additional females, particularly in populations in which the average group size is small and mortality is high.