The timing of fission among free-ranging Rhesus monkeys

Behavioral observations were carried out on a large group of free-ranging rhesus monkeys (Macaca mulatta) on Cayo Santiago from January 1968 to December 1969 and from October through December 1970. During this period, social group A divided. The 24-month study period can be classified into five stages which represent the different phases in the process of group fission. Two criteria for fission were established: the cessation of grooming between adult females of different sub-groups of the main group and the stabilization of the adult female population. The criteria were based on established information on group dynamics and inter-group behavior on Cayo Santiago. Several points became clear from the chronological analysis. Group fission is a long process. The duration of the process of fission and the specification of the season in which fission begins and is completed depends upon the definition applied. For purposes of this analysis, fission was defined as beginning with the onset of spatial fragmentation and corresponded to the initial part of the breeding season. The fission was completed during the breeding season. The duration of the process of fission was 18 months.     

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.     

Cardiac allograft pathology in Rhesus monkeys

Orthotopic, allogeneic heart transplantations were performed in 26 randomly selected rhesus monkeys to study the effect of immunosuppressive treatment on survival and cardiac morphology. The histological picture of the acute and chronically rejected hearts was similar to that described for acute and chronic cardiac allograft rejection in man. As seems to be the case in man, an obliterative arteritis of the coronary arteries appears to be the limiting factor in cardiac allograft survival in the rhesus monkey. Immunosuppressive treatment with either Imuran and ALS or Imuran, ALS, and Prednisone could not prevent the occurrence of obliterative arteritis of the coronary arteries. Contrary to the observation in man, no atherosclerotic changes were found in the affected parts of the coronary arteries or in the non-diseased parts.     

Rhesus monkeys attribute perceptions to others

Paramount among human cognitive abilities is the capacity to reason about what others think, want, and see--a capacity referred to as a theory of mind (ToM). Despite its importance in human cognition, the extent to which other primates share human ToM capacities has for decades remained a mystery. To date, primates [1, 2] have performed poorly in behavioral tasks that require ToM abilities, despite the fact that some macaques are known to encode social stimuli at the level of single neurons [3-5]. Here, we presented rhesus macaques with a more ecologically relevant ToM task in which subjects could "steal" a contested grape from one of two human competitors. In six experiments, monkeys selectively retrieved the grape from an experimenter who was incapable of seeing the grape rather than an experimenter who was visually aware. These results suggest that rhesus macaques possess an essential component of ToM: the ability to deduce what others perceive on the basis of where they are looking. These results converge with new findings illustrating the importance of competitive paradigms in apes [6]. Moreover, they raise the possibility that, in primates, cortical cells thought to encode where others are looking [7] may encode what those individuals see as well.     

Group changing in free-ranging male rhesus monkeys

Group changing behavior of maleMacaca mulatta was studied over a six-year period at the rhesus monkey colony on two coastal islands at La Parguera, Puerto Rico. Males first left their natal group at a mean age of 47 months and became solitary for the first time at a mean age of 64 months; all had left their natal groups by seven years of age. Age, mating season, sex ratios of adult males and females in the social bands, and geographical barriers all had significant effects on the group shifting. Population size, rank of mother or being an orphan did not significantly affect the changing process. Two factors, age (size) and seniority in the group, were important in determining a male's rank in his new group.     

Population growth of free-ranging rhesus monkeys at Tughlaqabad

A population of rhesus monkeys (Macaca mulatta) at the ancient site of Tughlaqabad on the southern outskirts of New Delhi, India, showed moderate growth throughout the 1960s and 1970s and very rapid growth in the last 4 years. Between July 1980 and July 1983, the population increased 79%, from two groups of 160 monkeys to five groups of 286 monkeys, an average annual increase of 21.4%. The natality of the population has been high, averaging 82.4% over three birth seasons. Mortality and disappearance rates, especially of juveniles and adults, have been remarkably low with total annual mortality averaging only 3.7% from 1980 to 1983. We believe the striking record of population growth in this population can be attributed to total protection, abundant food, good cover, a lack of predators, a generally improving habitat, and low disease. With the right combination of ecological and behavioral factors, rhesus populations can double in four years. The Tughlaqabad population provides important guidelines for the restoration and conservation of primate populations.     

Reproductive biology of captive and free-ranging spider monkeys

Records from 42 zoos and from long-term studies of wild populations were analysed to describe the reproductive biology of spider monkeys (Ateles spp.). Both data sets suggested that spider monkey females typically have their first infant between 7 and 8 years of age with an interbirth interval of approximately 32–36 months. Infant sex ratio for zoo populations was approximately 1 male to 1 female; infant sex ratios from wild populations were variable. Zoo records provided adequate sample size to suggest that interbirth interval was not influenced by the sex of the infant produced, and that the sex ratio and the probability of infant survival did not change with the number of infants the mother had produced. The findings of this study have implications with respect to the conservation of New World primate species. Since spider monkeys take a long time to reach sexual maturity and their interbirth interval is longer than that expected based on their body size, their populations may be slow to recover following disturbances. Thus, particular care should be taken for the protection of these species.     

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.     

Behavior of an all-juvenile group of Rhesus monkeys

The behavior and organization of a group of 33 juvenile rhesus monkeys removed from a single free-ranging group were found to parallel closely intact rhesus social groups. Dominance ranking among the juveniles was 95% predictable from prior knowledge of mothers' ranks. Grooming, sitting close together, sitting touching, and play were found to occur much more frequently between matrilineal kin than expected from random selection of partner. Some estrous behavior was observed, including two instances of peri-menstrual estrus. One lengthy homosexual interaction between two two-year-old females was observed. The basis of much of the behavior and organization shown by the juveniles was found to be the matrilineal kin bonds brought from their natal group.     

Control of postpartum mating behavior in free-ranging rhesus monkeys

This paper explores the effect that a dependent rhesus macaque infant (Macaca mulatta) has on the timing of its mother's resumption of mating. Toward this end, behavioral data from the rhesus populations at Tughlaqabad, India, and Cayo Santiago, Puerto Rico, are compared. Specifically, the intervals between parturition and subsequent resumption of mating for individual parous females are examined in order to shed light on the relative importance of environmental and internal factors (such as lactational infertility) in the control of rhesus mating behvior. At both study sites it was found that the later a given female gave birth during a birth season the shorter was her parturition-mating interval and the younger was her infant when she resumed mating activity. It is suggested that this finding is the result of an interaction of environmental and internal factors; both act in concert to determine how soon after parturition a particular rhesus female will resume mating activity.     

Playmate relationships of immature free-ranging Japanese monkeys at Katsuyama

The playmate relationships of immature Japanese monkeys were analyzed with respect to age, sex, and dominance rank class of the matrilines in a larger-sized free-ranging group. One-year-old immature males showed the largest number of play partners and the highest frequency of social play. Older immature females tended to play with younger animals of both sexes, whereas immature males of all ages played with same-sexed and like-aged peers. While high-ranking immature males continued their play partnerships with other animals until 4 years of age, middle/low-ranking males did not. The large number of peers and possible play partners may intensify their selectivity of play partners in relation to dominance. The forming of playmate networks by high-ranking immature males may explain the delay in group shifting of high-ranking animals.     

Urinary progesterone in free-ranging red howler monkeys (Alouatta seniculus): preliminary observations of the estrous cycle and gestation

The goals of this study were to develop and validate a radioimmunoassay (RIA) for measurement of unconjugated progesterone (P) concentrations in the urine of red howler monkeys (Alouatta seniculus) and to use urinary P profiles to characterize the reproductive cycle of this species. Analysis of P profiles from two females provided a preliminary estimate of the length of the estrous cycle (mean days +/- S.E.M. = 29.5 +/- 1.5; n = 2), and indicated that one female red howler copulated throughout two apparent estrous cycles. Urinary P concentrations during two confirmed pregnancies (211.8 +/- 29.7 ng P/ml) were higher (P < 0.05) than during the luteal phase (77.4 +/- 10.6 ng P/ml; n = 4) of the cycle.     

Thermoregulatory plasticity in free-ranging vervet monkeys,Chlorocebus pygerythrus

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 increased heterothermy (as indexed by the 24-h amplitude of their body temperature rhythm) in response to proximal environmental stressors. The mean 24-h amplitude of the body temperature rhythm in summer (2.5 ± 0.1 °C) was lower than that in winter (3.2 ± 0.4 °C), with the highest amplitude for an individual monkey (5.6 °C) recorded in winter. The higher amplitude of the body temperature rhythm in winter was a consequence primarily of lower 24-h minimum body temperatures during the nocturnal phase, when monkeys were inactive. These low minimum body temperatures were associated with low black globe temperature (GLMM, β = 0.046, P < 0.001), short photoperiod (β = 0.010, P < 0.001) and low rainfall over the previous 2 months, which we used as a proxy for food availability (β = 0.001, P < 0.001). Despite the lower average winter minimum body temperatures, there was no change in the lower modal body temperature between winter and summer. Therefore, unlike the regulated physiological adjustments proposed for torpor or hibernation, these minimum winter body temperatures did not appear to reflect a regulated reduction in body temperature. The thermoregulatory plasticity nevertheless may have fitness benefits for vervet monkeys.     

The reproductive biology of a free-ranging troop of Japanese monkeys

Quantitative data on the reproductive biology of Japanese monkeys (Macaca fuscata), especially of females, are reported here. Arashiyama B troop shows stable annual breeding periodicity, and has mating seasons between October and March. In mating seasons, females show estrus with rather consistent cyclicity, and are in estrus for a total of 35 days on an average. The mean length of estrous cycle is 34 days. Although most females show estrus inter-menstrually, some show peri-menstrually; i.e., estrus does not always synchronize strictly with ovulation. Pubescent females between 3.5 and 6.5 years show estrus, but with low sexual activity. Middle-aged females between 7.5 and 16.5 years show high sexual activity with high conception rate. Old-aged females over 17.5 years show low sexual activity. Females with surviving infants have lower sexual activity than those without infants. There is found no significant correlation between female's ranking and sexual activity. This study was financed partly by the Cooperative Research Fund of the Primate Research Institute, Kyoto University.     

Reproduction and population growth in free-ranging mantled howling monkeys

Free-ranging mantled howling monkey (Alouatta palliata Gray) females experienced a regular estrus cycle averaging 16.3 days, demonstrated sexual skin changes, and participated in multiple matings before becoming pregnant. Gestation averaged 186 days. The average interval between births was 22.5 months. Sexual maturity occurred at approximately 36 and 42 months for females and males, respectively. Female age at first birth was about 3½ years. Births were scattered during some years and clustered during others. The age, rank, and parity of the females affected infant survival. More female than male infants survived to one year of age. Increased population size was the result of immigration rather than births.     

Plasma lipoproteins of free-ranging howling monkeys (Alouatta palliata)

1. Plasma lipids and lipoproteins of free-ranging howling monkeys from Costa Rica (Alouatta palliata), aged 5 months to 23 years, were characterized. 2. High density lipoproteins were lipid-rich, similar to HDL2 of human plasma. 3. Fatty acid compositions of major lipid classes of very low, low and high density lipoproteins differed among social groups, possibly due to both dietary and genetic factors. 4. Low and high density lipoprotein phospholipids were enriched in phosphatidylethanolamine. 5. Howler plasma cross reacted with antihuman apoA-I antibodies but not with antihuman LDL antibodies. 6. No dimeric form of apoA-II was present, unlike human apoA-II.