Behavioral predictors of pairing success in rhesus macaques (Macaca mulatta)

Pairing Laboratory-Housed Adult Male Rhesus Macaques (Macaca mulatta): Success Rates in Relation to Behavioral Response and Duration of Visual Contact

While the benefits of pair housing have been well documented, less is known about increasing success in adult male macaque pair introductions. In this retrospective study, 95 unfamiliar adult male macaque (Macaca mulatta) pairs were examined to determine whether duration of visual contact, behavior, and age and weight were associated with success rate, with "success" defined as two weeks in full tactile contact without excessive behavioral indicators of incompatibility or injury requiring clinical treatment or care. Overall, the unfamiliar adult male pairs achieved a success rate of 72% and wounding requiring medical attention was rare (2%). A significant negative relationship between pair success and time in visual contact for pairs was found. Pairs who moved into tactile contact within 48-hours showed more positive social behaviors in protected and full contact and had a high rate of success (91%), while those who exhibited negative social behaviors were maintained in visual contact for longer. Nevertheless, rapid signs of compatibility were not necessary for the formation of successful pairs. While social introduction success rates steadily declined with increased periods of maintained visual contact, longer durations of 3 days to 1 week (70%), and 8+ days (58%), were still accompanied by high to moderate success, respectively. These results indicate that when negative social behavior is present early in visual contact success may be expected to decrease, but it is not necessarily indicative of incompatibility. Providing extra time in visual contact can reduce overall incidences of single housing.

Reducing stress and stereotypic behaviors in captive female pygmy slow lorises (Nycticebus pygmeaus)

Improving captive conditions of pygmy slow lorises (Nekaris and Nijman have recently suggested that the pygmy slow loris should be called the pygmy loris and is distinctive enough to warrant a new genus, Xanthonycticebu) (Nycticebus pygmeaus) poses many challenges because detailed aspects of their lives in the wild are incomplete. This hinders efforts to replicate sustainable environments for them. To improve their well-being in captivity, eight rescued female pygmy slow lorises at the Japan Monkey Center (JMC) were socially housed in two types of groups following their solitary housing: two pairs and one group of four individuals. They spent much of their time in affiliative behaviors, as well as sharing sleeping sites after placement in a social group. The purpose of my study was to examine whether social housing helped in reducing stress by comparing fecal glucocorticoids and stereotypic behaviors when housed alone and when with conspecifics. Overall, the levels of fecal glucocorticoids were significantly lower when socially housed than when kept alone. One individual exhibited stereotypic behavior when housed alone, but this behavior disappeared after social housing. These findings support recent evidence that pygmy slow lorises are social animals and will benefit from group housing in captivity. We conclude that social housing of pygmy slow lorises improves their well-being by reducing stress levels, and that their group housing in captivity can provide dividends for the conservation of this endangered nocturnal primate because lorises intended for release should find it easier to adapt to natural conditions.

Video Conference Technology as a Tool for Pair Introduction in Rhesus Macaques

Simple Summary

While pair housing macaques is known to improve welfare over single housing, the process by which animals are socialized can be stressful if the animals do not get along. To assess whether or not potential partners are compatible, they typically need to be located in visual contact with one another, which often involves moving one or both animals to a new location. Such relocations can cause stress for animals, particularly if the introduction attempt is not successful. In this study, we examined whether allowing rhesus macaques to interact via video conferencing technology (Zoom) could help us determine compatibility before they were relocated. We provided a Zoom session between partners for 42 pairs of monkeys and coded their behavior. We then examined whether these behaviors predicted future pair success. The monkeys in our study spent surprisingly little time attending to the screen, and attention did not predict pair success. However, the similarity of attention shown by individuals in the pair (e.g., amount displayed by the partners relative to one another) did. Pairs in which attention was primarily shown by one animal were more likely than others to be successful. While additional work is needed, video conferencing technology may help staff determine compatibility between potential partners.

Abstract

Pair housing is known to promote welfare for macaques in captivity. However, finding compatible partners can be challenging, particularly when animals are not located near one another. Because macaques show interest in videos of conspecifics, we examined the use of video conference technology (Zoom) as a potential tool to assess compatibility in 84 rhesus macaques (2–22 years old) prior to pair introduction. Monkeys involved in the pairs (12 female–female, 21 male–male, 9 female–male) were unfamiliar with each other. We set up a 10 min Zoom session between potential partners (on an iPad in front of the cage). We scored attention to the screen, anxiety, and prosocial behaviors and examined whether these behaviors predicted future pair success. Monkeys spent relatively little time attending to the tablet (median = 13.3%), and attention did not predict pair success (B = −0.06, NS). However, pairs in which attention was primarily shown by one animal had a higher chance of success than those in which both individuals showed similar levels (B = −4.66. p = 0.03). Neither prosocial (B = 0.89, NS) nor anxiety (B = −1.95, p = 0.07) behavior correlated with pair success. While preliminary, our data suggest that video conferencing technology may be useful as a tool for introducing unfamiliar partners prior to a socialization attempt.

Single-dose Diazepam Administration Improves Pairing Success of Unfamiliar Adult Male Rhesus Macaques (Macaca mulatta)

Social housing is one of the best forms of environmental enhancement for nonhuman primates, and current research into pair compatibility and introduction techniques focuses on improving safety and outcome. The gradual steps method (GS), which is widely used for introducing indoor-housed macaques, involves an initial phase of limited physical contact to allow animals to acclimate to one another prior to full contact. A safer, more efficacious introduction method is needed. The administration of diazepam, a sedating anxiolytic medication, is known to increase affiliative behavior in familiar, socially housed rhesus macaques. We hypothesized that administration of a single dose of diazepam prior to full contact introduction without a protected contact phase would improve the success rate of isosexual introductions of unfamiliar macaques as compared with the success rate of GS. We administered 3.2 mg/kg oral diazepam to 34 adult male rhesus macaques (Macaca mulatta) 30-45 min prior to introduction into full contact. Pairs were deemed successful after 14 consecutive days of compatible full-contact housing. Behavioral data collected during these introductions was compared with data collected on 58 adult males during social introductions using GS. Sixteen of 17 introductions (94%) employing diazepam were successful. This success rate was significantly higher than the 45% success rate of introductions using GS. We also found that a longer duration of single housing and increased age were predictive of pair failure in animals introduced using GS. Our results suggest that diazepam administration prior to full contact introductions increases the success rate of male social introductions.

Sex Differences in Hierarchical Stability in a Formation of a Mixed-sex Group of Rhesus Macaques

Forming groups of captive rhesus macaques (Macaca mulatta) is a common management practice. New formations of unfamiliar macaques can be costly, with high levels of trauma, particularly as intense aggression is used to establish a dominance hierarchy. Combining previous subgroups into one new group may be beneficial, as some individuals already have established dominance relationships. We tested this hypothesis by forming a new mixed-sex group of rhesus macaques that combined an established group of females with an established group of males. Prior to the mixed-sex group formation, both the female and male hierarchies had been stable for 3 y; after mixed-sex group formation these hierarchies were maintained by the females and were initially maintained by the males for 3 wks. However, the temporary hospitalization (due to a laceration caused by aggression) of the alpha male destabilized the male hierarchy. Age and weight then predicted male rank. Temporary hospitalizations resulted in rank changes for the males, evidenced by reversals in subordination signals. This study indicates that using established groups of familiar individuals may maintain female hierarchical stability in a mixedsex group formation, but further research is needed to understand how to maintain and predict male hierarchical stability to reduce trauma. Improved knowledge of hierarchical stability would be invaluable to managers of large rhesus macaque groups and would help improve the welfare of captive rhesus macaques.

Temperament Predicts the Quality of Social Interactions in Captive Female Rhesus Macaques (Macaca mulatta)

Previous reports suggest that female macaques with greater similarity in emotionality and nervous temperament, as evaluated in a well-established BioBehavioral Assessment (BBA) at the California National Primate Research Center, were more likely to form successful pairs. We tested whether the same measures can also predict the quality of social interactions among 20 female rhesus macaque pairs. We correlated the pairs' emotionality and nervous temperament scores obtained in infancy and the levels of behaviors recorded systematically during the pairing process years later. Supporting previous findings, partners with similar emotionality scores were more affiliative, and pairs with similar nervous temperament expressed less dominance/submissive behavior. Exploratorily, we found that pairs that were better at processing social information (part of BBA) were also more anxious. Such animals should be prioritized to be introduced in rooms that house calmer, less aggressive animals and provide opportunities for hiding to alleviate their anxiety. Indeed, positive social experiences not only promote animal welfare, but also reduce stress related confounds and unexplained data variability. Therefore, by incorporating the animals' temperament into the pair configuration process we increase the likelihood of forming high-quality pairs, both in terms of welfare and the research of which they are a part.

Self-Injurious behavior in rhesus macaques: Issues and challenges

Some monkeys housed in research facilities develop abnormal behavior ranging from stereotypic to the more serious condition of self-injurious behavior (SIB). We initially sought to understand how and why monkeys engaged in SIB and more importantly why only a small percentage of laboratory monkeys, with seemingly similar housing and background, developed this disorder. Of particular importance was the recognition that different pathways might lead to SIB and that strong individual differences would affect the manifestation of this disorder and the response to treatment. We developed a comprehensive plan to identify effective treatment and prevention strategies. We started with characterizing the disorder in terms of prevalence and types of environments in which it was found. We then conducted observations on a cohort of SIB and control monkeys to identify conditions associated with SIB (e.g., disordered sleep) as well as clinical disease states and congenital defects that could be precipitating factors. We examined the environmental events that triggered episodes of SIB in monkeys with the disorder and evaluated three models that might explain the reinforcement contingencies associated with SIB, including tension reduction, self-stimulation, and social communication. Possible treatments for SIB such as environmental enrichment, social housing, and pharmacotherapy were tested by our group and others. To date, no single treatment has been found to abolish SIB, and each of these treatments is impacted by individual differences. To develop possible prevention strategies, we examined colony management and health records to find risk factors for SIB. These risk factors generalized to other facilities, and considerable effort was expended by all behavioral managers at these facilities to reduce early life stress exposure, to minimize the length of individual cage housing by emphasizing pair housing, and to reduce the possible stressfulness of various veterinary/medical procedures by implementing positive reinforcement training.