Vocal recognition in free-ranging vervet monkeys

Screams of free-ranging juvenile vervet monkeys were played to a group containing their mothers and two ‘control’ females who also had offspring in the group. Mothers and controls were separated from their offspring at the time. Mothers' responses showed significantly shorter latency and longer duration than controls'; mothers were also significantly more likely to approach the speaker. Playbacks significantly increased the probability that controls would look at the mother; a majority of controls did so without any apparent cue from the mother. Results demonstrate that adult female vervets can distinguish their offsprings' screams from those of other immatures, and they suggest that vervets are able to associate specific screams with specific individuals and these individuals with their mothers.     

Living in the suburbs: Space use by vervet monkeys (Chlorocebus pygerythrus) in an eco‐estate,South Africa

We examined vervet monkey (Chlorocebus pygerythrus) space use using GPS/UHF telemetry data from 10 vervet monkeys across six troops over 9 months within a 420 ha suburban eco‐estate. We documented a mean home range of 0.99 km² (95% MCP) and 1.07 km² (95% KDE) for females (n = 6), 1 km² (95% MCP) and 1.50 km² (95% KDE) for males (n = 4) and 0.87 km² (95% MCP) and 1.12 km² (95% KDE) for troops (n = 6), respectively, indicating that males and larger troops had larger home ranges. These relatively small home ranges included shared territorial boundaries and high home range overlap. Vervet monkey movements indicated higher morning activity levels, and habitat selection indicated significantly more use of golf course, urban residential and forest, thicket and woodland areas, and avoidance of wetland, grassland and shrub, and urban built‐up areas. Our results suggest that modified habitat use by vervet monkeys is a consequence of behavioural facilitation to access highly available food resources, thereby facilitating their persistence in green spaces in urban areas of South Africa. Conflict management is dependent on the conservation of sufficient natural habitats and food resources, to minimise their dependence on anthropogenic supplementary food resources and consequently reduce human–monkey conflict.     

Group extinction and fusion in free-ranging vervet monkeys

Three cases of group fusion were observed among vervet monkeys in Amboseli National Park, Kenya, during the 1984 drought. In all cases, group fusion involved the migration of at least two females into a small neighboring group. Following migration, the females' natal groups ceased to exist. Although migrants initially assumed low ranks, none received high rates of aggression, and two rose in rank 6 months after their arrival. Migrant females appeared to employ a number of “strategies,” including grooming, allomothering, participation in intergroup encounters, and the formation of coalitions against males and each other to hasten integration. Results suggest that the causes of male and female migration differ fundamentally, and that group fusion occurs primarily in response to the inability of small groups of females to compete successfully with other groups for resources.     

Early infant development and maternal care in free-ranging vervet monkeys

The interactions of infant vervet monkeys (Cercopithecus aethiops) with their mothers were examined during the first 12 weeks of life. During this period there was a gradual rise in behaviour associated with increasing independence from the mother: female infants were slightly advanced over males on measures of decreasing contact with mothers and increasing rejections from the nipple. There were differences between the mothers in the ways they interacted with their infants such that no consistent maternal styles could be defined. Dominance rank of the mother did however influence her behaviour towards her infant, and high ranking mothers tended to be less rejecting towards sons, but more rejecting towards daughters, than were low ranking mothers. It is suggested that since vervet mothers have access to allomothers they may not be limited to dichotomous mothering styles.     

Pregnancy outcome in free-ranging vervet monkeys (Cercopithecus aethiops)

A preliminary assessment of individual female differences in conception rate and fetal wastage has been determined for a population of wild vervet monkeys (Cercopithecus aethiops). One of three troops of vervet monkeys, the subjects of a long-term behavioral study, was trapped and blood was obtained for electrophoretic analysis. Pregnant females exhibited a distinctive serum aminopeptidase phenotype allowing a conclusive determination of pregnancy. Of the seven females diagnosed as pregnant, three later gave birth. Of the females that aborted, two were nulliparous and one was very old. Studies of captive animals have indicated that age and rank may affect a female's ability to carry a fetus to term. These factors, rather than the trapping procedure, may have been responsible for most of the fetal loss in the trapped troop. A comparison of all three troops for a 3-year period indicated that there were fluctuations in yearly birth success of individual females, as well as a relatively high miscarriage rate. The results of this study indicate the advantages of obtaining joint behavioral and biological data.     

Genital signalling and the coexistence of male vervet monkeys (Cercopithecus aethiops pygerythrus)

To ascertain the social significance of male genital colouration two troops of vervets, one free-ranging and one caged, were observed. It was found that genital signals were associated with intermale agonism. It is suggested that this communicatory system regulates the behaviour of competitors and may thereby have facilitated the evolution of a multimale social system.     

Characteristics and regulation of the ovarian cycle in vervet monkeys (Chlorocebus aethiops)

This study was designed to evaluate the timecourse of ovarian and pituitary endocrine events throughout the menstrual cycle in the vervet monkey, and whether circulating luteinizing hormone (LH) or the uterus regulates the functional lifespan of the vervet corpus luteum. Daily saphenous blood samples were collected from adult females (1) during spontaneous menstrual cycles (n = 7), and (2) during cycles in which a gonadotropin-releasing hormone antagonist (acyline) was administered for 3 days at midluteal phase (n = 3), and (3) for 30 days following recovery from hysterectomy (n = 4). Estradiol (E) and progesterone (P) levels were assayed using electrochemoluminescent assays. Gonadotropin levels were measured by radioimmunoassay using reagents developed for the assay of follicle-stimulating hormone and LH in macaques. Spontaneous cycles exhibited a midcycle E rise (476+/-49 pg/ml), engendering an LH surge, 12+/-1 days after onset of menses, followed by a luteal phase with peak P levels of 4.7+/-0.9 ng/ml. Histologic evaluation of the ovaries at late follicular phase or early luteal phase revealed the presence of a single, large Graafian follicle or developing corpus luteum, respectively. Acyline treatment caused a significant (P<0.05) decline in P levels (2.9+/-0.5 vs 0.5+/-0.3 ng/ml, 0 vs 48 h post-treatment) and premature menstruation compared with untreated controls (P<0.05). Hysterectomy had no apparent effect on the monthly pattern or levels of circulating E or P. Thus, the characteristics and regulation of the ovarian cycle in vervets appear similar to those in women and macaques, with cyclicity dependent on pituitary gonadotropin hormones and independent of a uterine luteolytic factor.     

Hematological changes in vervet monkeys (Chlorocebus aethiops) during eight months' adaptation to captivity

This study investigated fluctuations in hematological values of 50 wild-caught vervet monkeys (African green monkeys, grivets, Chlorocebus aethiops) during habituation to captivity. The monkeys were categorized into four groups according to age and sex viz adult males, adult females, juvenile males, and juvenile females. The erythrocyte values were significantly higher (P<0.05) in the adult males than in the other animals. There was an increase in most of the erythrocyte parameters studied during the monitoring period with the most significant being hemoglobin, hematocrit, and mean corpuscular volume. However, the red cell distribution widths, which were higher in adult females, declined. The total white blood cell (WBC) counts, which were higher in adult females than in the other animals, were closely correlated with granulocytes counts. The WBC levels decreased in all the animals throughout the 8 months study, indicating gradually decreasing stress, but they were relatively stable in males. The platelet counts declined significantly (P<0.05) and at 8 months post capture the counts were higher in females than in males. The juvenile female platelet counts were relatively stable during the monitoring period. The maintenance of the monkeys on an improved stable diet and in environment-controlled housing combined with progressing psycho-physiological adaptation may be important factors for the gradual improvements of the hematological values recorded. There were wide variations in these between individual animals emphasizing the need for long adaptation combined with establishment of individual baseline values before experimental studies.     

Contact with human facilities appears to enhance technical skills in wild vervet monkeys (Chlorocebus aethiops)

Technical abilities of primates are typically tested in the laboratory. It has been argued that close contact between animals and humans may lead to an increase in skills due to an 'enculturation' of subjects. Here, we provide evidence that exposure to human facilities may improve wild vervet monkeys' technical skills in a social learning task using the 'artificial fruit' approach. Two of our 6 study groups had access to human facilities within their territories. Only members of these 2 groups were likely to open successfully 'artificial fruit' during their first attempt. Success appeared to be independent of individual sex or the type of task. Our results highlight the possibility that human enculturation may allow captive monkeys to acquire more technical skills than their wild counterparts, and we suggest that this possibility should be tested in further field experiments.     

Negotiations over Grooming in Wild Vervet Monkeys (Chlorocebus pygerythrus)

Mutual grooming plays a central role in the establishment and maintenance of social relationships in primates. Allogrooming has two main functions: hygiene and bonding with partners. The duration of grooming bouts is commonly used in studies of the functional aspects of grooming, but few reflect on the proximate mechanisms that determine grooming bout lengths. As it is highly unlikely that groomer and groomee prefer exactly the same bout length, we are likely to observe the result of some form of negotiation. We currently lack information about the signals that primates employ to inform others about their intentions and desires concerning grooming interactions. From October 2006 until April 2007 we studied three behaviors shown in grooming interactions that could potentially have a signaling function in the negotiation process over the initiation and length of grooming bouts among adult females of two vervet groups freely ranging in the Loskop Dam Nature Reserve, South Africa: approaching another individual as far as that resulted in a grooming session, changing of the body position by the groomed individual, and lip smacking. We found that “approach” did not reliably predict which individual would receive grooming first, although approaching individuals groomed significantly more than those approached. Thus, in the context of grooming interactions, moving toward a group member may signal the willingness to invest. Body part presentations appeared to be the main signal used to demand a prolongation of the grooming by the partner. Finally, lip smacking was used under potentially stressful circumstances, notably shortly before using the mouth to groom the partner or an attempt to touch a mother’s infant. Our exploratory study hopefully inspires colleagues to start looking at the role of communication during cooperative interactions for a better appreciation of how animals manage cooperation and negotiate exchange rates.     

Vitamin A toxicity in wild-caught African green vervet monkeys (Chlorocebus aethiops) after 2 years in captivity

Primate lab diets typically contain high vitamin A concentrations when compared with human recommended intakes. In this study, we analyzed the vitamin A contents of liver and serum from 13 adult female African green vervet monkeys (Chlorocebus aethiops). These monkeys were wild-caught and held in captivity for 2 y, during which time they consumed a standard primate diet. Liver vitamin A concentration (mean +/- 1 standard deviation) was 14.6 +/- 2.3 micromol retinol/g liver; subtoxicity in humans is defined as at least 1 micromol/g liver. The serum retinol concentration (0.93 +/- 0.21 microM) was not elevated. Hypertrophy and hyperplasia of hepatic stellate cells were present which, in conjunction with elevated hepatic vitamin A concentrations, are evidence of toxicity. Although the ramifications of chronically toxic vitamin A status in experimental monkeys have not been defined, this state may influence nonhuman primate research outcomes and confound data interpretation. The validity of bone mineral research using nonhuman primates is of greatest concern, in light of the association between vitamin A toxicity and compromised bone health.