Cayo Santiago Research Articles

Comparison of three rhesus groups for antibody patterns to some viruses: absence of active simian virus 40 transmission in the free-ranging rhesus of Cayo Santiago.

Comparison of three rhesus groups for antibody patterns to some viruses: absence of active simian virus 40 transmission in the free-ranging rhesus of Cayo Santiago.

Seasonal breeding of free-ranging rhesus monkeys and related ecological factors.

The seasonal appearance of mating activities and births of rhesus monkeys in a free-ranging colony on two small islands near La Parguera, Puerto Rico, were recorded from the founding of the colony in 1962 to August 1966. Mating activities began in late August or September, reached a peak during November and December, and ceased in March or April. Except for a wide spread early in the colony's history, births were confined to the period from March to July, with 74% occurring during May and June. Lactating females began mating activities later than non-lactating females. The onset of mating typically followed vegetation changes associated with a period of high rainfall in late summer. The correlation between rainfall and mating activities, perhaps resulting from vegetational changes, also appears to be present at Cayo Santiago, another island colony of monkeys, and in Northern India, the natural home of the rhesus monkey.

Ecology and Activity of Himalayan Foothill Rhesus Monkeys (Macaca Mulatta)

Himalayan foothill rhesus monkeys were studied for a year at three forest habitats and in the town of Haldwani in Uttar Pradesh, India. Food supplies in the forest diminished both in abundance and variety as altitude increased during the ascent from tropical forests at the base of the foothills to subtropical pine and temperate oak forests at elevations of 5000 ft or more. Home range, day range, population density, and activity patterns also varied with altitude: monkey troops in the less favorable areas had larger home ranges and day ranges and were more often on the move during the day, while the lower elevations had a higher population density of monkeys. Increased mobility was a characteristic of one subtropical pine forest troop lacking any adult male. Both the abundance of food in Haldwani and the limited tolerance of the human inhabitants limited home ranges there to about 0.02 mi2, approximately 1/20 that of the smallest forest troop home range. Activity patterns were more stereotyped in the town than in the forest. The population density of the occupied portion of town was much more than in the forests, but less than on Cayo Santiago. Night time activity is probably greater in town.

Sociobiology of Rhesus Monkeys Iii: the Basic Communication Network

AbstractThe observed distribution among age-sex classes of socially significant behavior in free-ranging rhesus monkeys on Cayo Santiago was tested against a series of progressively stronger null hypotheses. The first hypothesis was of purely random interactions, in which it was assumed that all individuals were equally likely to interact, all were as likely to be actor as to be object of any social signal, and all chose their social partners at random. This model proved untenable. In particular, adult males and females interacted with each other much more often than expected from the random model, and adult males interacted more often than expected with other males, both adult and juvenile. Juvenile females tended to interact relatively infrequently with other animals of any age-sex class. Adult males and juveniles of both sexes seldom interacted with infants. A second model, which took into account these age changes and sex differences in reactivity, but ignored the possibility of social preferences and assumed that interactions could be predicted from the overall reactivity or sociability of the monkeys involved, was also inadequate to account for the observed results. Apparently rhesus social behavior not only changes with age and differs with sex, but also is affected by "attractions" and "repulsions" within the group. The result was frequent interaction between adult males and females, between adult females and infants, and among juvenile males. Juvenile females, despite their general nonsociability, were apparently attracted to juvenile males, with whom they intracted more often than expected. Males, both adult and juvenile, tended to avoid infants, and vice versa. Adult males tended to avoid and to be avoided by juveniles of both sexes. Finally, the effects on paired interactions of these age changes, sex differences attractions and repulsions constitute a new model expressed in the form of an action constant and a receptivity constant for each age-sex class, and two interaction constants for each pair of age-sex classes. A method is given for extrapolating the results to populations with other compositions.

Nonbreeding Activities of Three Adult Males in a Band of Free-Ranging Rhesus Monkeys

A study of the diurnal activity pattern in relation to rank and social behavior was conducted just prior to the mating season in a free-ranging band of rhesus monkeys (Macaca mulatta) on Cayo Santiago, Puerto Rico. One hundred and thirty hours were spent observing the dominant, the fifth-ranking and the eleventh-ranking males of an adult male social hierarchy of 12 individuals. The three monkeys spent most of their time resting, feeding or grooming. Differences between monkeys based on individual characteristics and social rank are pointed out. Social encounters were frequent, but these occupied little of any monkey's time. In this study, activity patterns depended on a combination of individual characteristics, social rank and interaction with other individuals.

The development of social structure in free-ranging rhesus monkeys.

The development of a social structure within a new colony of free-ranging rhesus monkeys was studied during their first 44 months on two adjacent islands, La Cueva and Guayacan, off the arid southwestern coast of Puerto Rico near La Parguera. Two of the nine social bands that formed in the colony disintegrated, two were removed to be held in enclosures, and five remained free-ranging. The observations on the development of social bands indicated that: (1) females experienced less difficulty in forming stable social units than males, (2) bands typically developed from a basic group of adult females dominated by an adult male, (3) the basic group of adult females was the most stable portion of the band and determined the rank of the band relative to other bands, (4) the presence of a dominant adult male was essential for the survival of the band as a social unit and, (5) males that did not join bands either remained semi-solitary or formed all-male groups. Stabilization of the social structure within and between bands was a gradual process. Inter-band shifts did not decline in frequency until two years after the colony's founding and many males did not join heterosexual bands until two and one-half years after the colony was founded. Attempts to form bands by artificially holding monkeys together for a period of time before releasing them were of limited success. Of four such attempts, only portions of two released groups remained together to form free-ranging social bands. Comparison between these results and those on a more mature population of free-ranging monkeys at Cayo Santiago indicates that the absence of kinship ties in the new colony may have been the cause of the instability observed.

Free-ranging rhesus monkeys: age and sex differences in individual activity patterns.

Two hundred thirty of the feral rhesus monkeys on Cayo Santiago were observed individually for postural adjustments, locomotor behavior, manipulation, and other nonsocial activities. Both form and frequency of activity were influenced strongly by age; sex differences were minimal. Most activities decreased with age, but head movements, presumably reflecting visual scanning, were more frequent in adults.

A Three‐Year Study of Mating Behavior in a Freeranging Band of Rhesus Monkeys

The mating behavior of a freeranging band of rhesus monkeys in an island colony near Puerto Rico was studied for three consecutive years. From approximately July through December females had repeated cycles of estrous behavior in which they associated closely with males, groomed with them, and engaged in copulation. About one—half of the females which conceived had postconception estrous periods, including copulation. The average number of estrous periods per female was two, each period lasted an average of 11 days, and most estrous cycles lasted about 28 days. An average of three males associated with a female during one period. Most females began breeding when they were three years old and there was no significant difference between the mating activity of females three, four, and five years old. Six—year—old females showed a definite increase in mating activity, and females seven years old showed a still greater increase. No significant increase was apparent after the females reached seven. The females' rank in the dominance hierarchy apparently had no effect on their mating activity. The quantity of the males' sexual activity was generally correlated with their dominance rank. The highest male was the most active by far, the first to become active, and the only male to form many exclusive consort relationships with individual females. Progressively lower ranking males were usually less active, but low—ranking males were active early and late in the mating season. The findings concerning average period and cycle length, number of males associating with females, and the relation between the males' rank and mating activity agree closely with those of C. R. Carpenter (1942) on Cayo Santiago in 1940. Though several promising lines of inquiry have been opened, much work remains to be done before we can explain the relation between rhesus mating behavior and its physiologic basis, or explain variations in reproductive periodicity.

Sociobiology of rhesus monkeys. II: Stochastics of social communication

The behaviour of an individual depends upon preceding actions within the individual's interacting group. Such antecedent events do not, however, completely determine present behaviour. Rather, probabilistic constraints exist between events within a sequence of actions. Such sequential dependencies between the actions of group members indicate that social communication is taking place. These communicative constraints in sequences of behaviour may be represented by stochastic processes. The sequential constraints in the social communication of rhesus monkeys are given in a series of stochastic models that specify the probabilities of all events and all sequences of events. Estimates of these probabilities were obtained during a two-year field study of rhesus monkeys on Cayo Santiago, an island in the West Indies. Each model considers the constraints from an earlier antecedent than did the last model in the series. Thus, each model forms the null hypothesis for the next one, and is replaced by it because the new model reduces the uncertainty of our predictions of behaviour. This uncertainty is measured, using a method developed in the mathematical theory of communication. This measurement readily leads to several related ones, including an index of behavioural stereotypy. The results are consistent with the theory that rhesus monkeys base their social behaviour upon their memory for preceding events in their social group, and that this memory extends back beyond the immediately antecedent event. The behaviour of the monkeys, considered as isolated events, had an uncertainty of 4·8 bits, out of 6·9 bits maximum for a species with a repertoire of 120 behaviour patterns. Approximately 1·9 bits of information were picked up by the monkeys from the immediately antecedent behaviour in their social group, thus reducing the uncertainty of their behaviour to 2·9 bits. Further reductions resulted from information from still-earlier events in their social group, although the influences of such long-term constraints on behaviour were progressively more difficult to estimate. As a result of these stochastic contingencies, it was possible to measure the degree of stereotypy of the monkeys' behaviour. The index of stereotypy had a value of 0·3 for isolated events, 0·6 for events considering just the immediate antecedent behaviour in the group, and higher values for longer sequences. The development of such probabilistic models involved several sources of error and certain implicit assumptions. They should not be used without cognizance of these limitations. When properly used, however, they should enable one to predict the social behaviour of rhesus monkeys with a far greater accuracy than has previously been possible.

A Survey of Intestinal Parasites in a New Colony of Rhesus Monkeys

A survey of intestinal parasites was made of the rhesus monkeys in a free-ranging colony off the southwestern coast of Puerto Rico. Sixty-eight per cent of 99 monkeys examined were found to harbor intestinal parasites. The most common organisms were Entamoeba coli, E. histolytica, and Strongyloides. Viable Strongyloides ova were recovered from soil samples. Hermit crabs ingest monkey feces and may serve as agents in the dispersal of intestinal parasites. This study records the results of a survey of the intestinal parasites in free-ranging and confined rhesus monkeys (Macaca mulatta) on La Cueva and Guayacan islands off the southwestern coast of Puerto Rico. There were no monkeys on these islands until December 1961, when ten animals from Cayo Santiago, another rhesus colony in Puerto Rico, were introduced. During 1962 6 more were transferred from Cayo Santiago and 254 were imported from India. After high initial mortality the colony stabilized, and during the period of this study (February 1963 to April 1964) it contained approximately 150 monkeys. Most of these ranged freely on the islands, but some were confined in large enclosures and a small number were held in individual cages. The purpose of this study was to determine the incidence of infection in a newly established colony and to draw comparisons with another such survey (Poindexter, 1942). A parasitological survey of the monkeys on Cayo Santiago was made by Poindexter (loc. cit.) to determine the cause of a mild epidemic of diarrhea in the colony. His survey was made 3 years after the colony was established. He examined 151 fecal samples collected from 122 monkeys. Of this number 99% were found to harbor parasites. Protozoan parasites occurred most frequently, the more prevalent being Received for publication 19 September 1964. * Present address: St. Mary's College of Maryland, St. Mary's City, Maryland. 294 Balantidium simile, Entamoeba coli, and E. histolytica. Among the helminths heavy infections of Strongyloides papillosus and Oesophagostomum bifurcum were present.

SOME ASPECTS OF PARENT-OFFSPRING AND SIBLING RELATIONS IN A GROUP OF RHESUS MONKEYS, WITH A DISCUSSION OF GROOMING.

AbstractObservations of a group of rhesus monkeys living on Cayo Santiago, Puerto Rico show (1) that a rhesus female and her offspring can continue to maintain a distinct relation into the offspring's physical maturity, and (2) that the offspring often develops its strongest relations with monkeys of its own genealogy. Detailed descriptions of relations in several of the genealogies illustrate the above points. The observer identifies relations by the consistent close spacing of individual monkeys, by incidents, such as fights, and by frequency of interactions, such as grooming. Grooming behavior is described. Provisional categories of motor patterns of rhesus monkey grooming are the slide, scrape, and pick. Apparent differences in intensity of grooming may be due to differences in number of slides, scrapes, and picks per time interval, differences in the sequences of the three categories within a bout, and differences in the area covered by each movement. Sequences of slides, scrapes, and picks interrupted by other behaviors, such as scratching, make up grooming bouts. Grooming bouts occur in sequences with bouts of other behavior such as locomotion, fighting, sleeping. Grooming seems to serve a variety of functions although a common element is the relaxing effect on the participants. Monkeys both solicit grooming from others, and groom others without being solicited. Grooming sometimes placates an aggressor following a fight. Monkeys sometimes seem to anticipate aggression and forestall it by grooming the potential aggressor. The case histories of grooming relations show that each relation is unique and is always changing, at least slightly. The human family may have originated when symbolic definition and generalization was given to some such system of behavioral relations already present in populations of the ancestors of the human species.

Estrous Cycles and Mating Behavior in a Free-Ranging Band of Rhesus Monkeys

The introduced rhesus monkeys on Cayo Santiago, Puerto Rico, have an annual reproductive cycle with estrous periods limited to the months from July to January. The most intensive breeding occurs in September and October. The periodicity of estrus in the 34 mature females of one social group was studied during the 1960 breeding season. Among the 28 which gave birth, 20 apparently conceived during the first estrous period, 6 did not conceive until the second and the time when 2 conceived was uncertain. Distinct estrous periods occurred during the early part of gestation. Thirteen of the 28 pregnant females had at least one such postconception estrous period. Higher ranking males were in general more active breeders than lower ranked animals, but breeding activity did not decrease with decreasing dominance in a regular and predictable manner. Aggression among males as a result of competition for estrous females was not seen.