Temperament differs among individuals both within and between species. Evidence suggests that differences in temperament of group members may parallel differences in social behavior among groups or between species. Here, we compared temperament between three closely related species of monkey - rhesus (Macaca mulatta), long-tailed (M. fascicularis), and pigtailed (M. nemestrina) macaques - using cage-front behavioral observations of individually housed monkeys at a National Primate Research Center. Frequencies of 12 behaviors in 899 subjects were analyzed using a PCA to identify temperament components. The analysis identified four components, which we interpreted as Sociability towards humans, Cautiousness, Aggressiveness, and Fearfulness. Species and sexes differed in their average scores on these components, even after controlling for differences in age and early-life experiences. Our results suggest that rhesus macaques are especially aggressive and unsociable towards humans, long-tailed macaques are more cautious and fearful, and pigtailed macaques are more sociable towards humans and less aggressive than the other species. Pigtailed males were notably more sociable than any other group. The differences observed are consistent with reported variation in these species’ social behaviors, as rhesus macaques generally engage in more social aggression and pigtailed macaques engage in more male-male affiliative behaviors. Differences in predation risks are among the socioecological factors that might make these species-typical behaviors adaptive. Our results suggest that adaptive species-level social differences may be encoded in individual-level temperaments, which are manifested even outside of a social context.

The Mariana Crow Corvus kubaryi is a Critically Endangered species found only on the island of Rota, Northern Mariana Islands. It was extirpated from the neighbouring island of Guam by the introduced brown tree snake Boiga irregularis and the Rota population has been in decline since at least 1995. We identified only 60 pairs present on Rota in 2007 compared with an estimated 117 pairs in 1998, a decline of nearly 50% in nine years. The decline may be linked to proximity to human activities, though more data are needed. We monitored 204 crow nests between the 1996 and 2009 breeding seasons. Crows initiate clutches between August and April. The overall estimate of nest success was 25.7% ( n = 204). On average 49% of pairs produced at least one fledgling per season. The mean number of fledglings per pair per year is 0.66. Mean clutch size was 2.6 ( n = 82), mean number of nestlings was 1.4 ( n = 106), and mean number of fledglings per nest was 1.3 ( n = 68). Daily survival rates declined in later years, and increased during the nest cycle. The number of pairs with successful nests did not change during the study period, nor did the number of fledglings per pair. Predation appeared to be the primary cause of nest failure. The breeding season lasted around nine months and pairs re-nested after failure. Predation of adults and juveniles by cats, combined with possible inbreeding depression, habitat disturbance and human persecution appear to be the cause of decline of the Mariana Crow. We strongly recommend a programme of invasive predator control, habitat maintenance, and captive rearing to ensure the species' survival.

We assessed developmental stability and context generalizability of temperament in pigtailed macaques (Macaca nemestrina) from the University of Washington Infant Primate Research Lab. A principal components analysis condensed 6 behavioral measures into 2 components, interpreted as reactivity and boldness. Changes in these measures over the 1st 10 months of development showed a trend toward calmer and bolder behavior with age, with significant individual variation in the pattern of change. Boldness showed a quadratic pattern of change, whereas reactivity decreased linearly. We also studied the relationship between temperament and response to a novelty probe. The magnitude of the response to the novelty probe decreased slightly over time, and boldness and reactivity in a familiar setting did not predict these changes in response to novelty. In a 2nd principal components analysis, reactivity to novelty represented a distinct aspect of temperament. Our results demonstrate developmental changes and context dependency in macaque behavior.

Past research has shown that aggressive behaviors can affect female reproductive outcome in non-human primate captive breeding programs. In this study, aggressive behaviors were recorded in a colony of pigtailed macaque monkeys (Macaca nemestrina) and related to pregnancy outcome. For twenty-two weeks, behavioral data were collected from nine breeding groups, consisting of zero to one male (some males were removed after a cycle of conceptions for husbandry reasons) and four to eight females. Observations included all occurrences of eleven aggressive behaviors during 15-minute observation sessions, one to three times a week. Mean weekly aggression levels during the study period were determined for each group, as well as for each pregnancy. Aggression data were summarized with Principal Components Analyses (PCA). Results indicate that pigtailed macaque aggression falls into five distinctive categories: warn, engage, threaten, pursue, and attack. Breeding groups differed in their levels of aggression, even after controlling for group size, presence of a sire, and group stability. Levels of the five aggression categories were found to affect the probability that a pregnancy ended in either a natural birth of a live infant, a clinical intervention producing a live infant, or a nonviable outcome. The predictive value of aggression was significant when clinical interventions were included as possible reproductive outcomes, Behavioral observation of captive groups could identify “risk” conditions affecting pregnancy outcome and the requirement for clinical intervention.

Personality change in nonhuman primates is a topic that warrants more research attention. Many studies focus on intraindividual repeatability, but few note population-wide trends in personality change. In part, this results from the large sample size that is required to detect such trends. In the present study, we measured personality in a large sample (N = 293) of adult, mother-reared pigtailed macaques, Macaca nemestrinam, over a period of 3 years. We looked at four personality components (sociability towards humans, cautiousness, aggressiveness and fearfulness) derived from behavioural observations at two to four time points per subject. We found these components to have repeatabilities similar to those reported elsewhere in the literature. We then analysed population-wide changes in personality components over time using a linear mixed effects model with three predictors: entry age at the current primate facility, tenure at the primate facility at the time of the first personality test and time elapsed since the first personality test. We found that adult personality changed with life experiences (here, tenure at the facility where tested) and age. Throughout adulthood, pigtailed macaques became less cautious and more aggressive. At the same time, subjects became less cautious and more sociable with increasing time in individual caging at the current primate research facility. We also found that individuals differed significantly in their personality consistency. Other researchers may benefit by applying similar methodology to that described here as they extrapolate about personality measures over time.