Efforts to promote the psychological well-being of captive non-human primates through the application of environmental enrichment techniques are becoming more common. However, from this perspective relatively little empirical work has been done on the effects of manipulation of the social environment. The data currently available indicate that primates kept in solitary confinement are likely to develop a variety of behavioural and physiological disturbances reflecting reduced well-being, whereas most compatibly socially housed primates appear better adapted. There is always some risk associated with manipulating the social environment for experimental or husbandry reasons, but the risk of deleterious consequences can be reduced by a good knowledge of the animals’ normal repertoire and careful monitoring of how the animals adjust to the new conditions. Attending to the social environment of captive primates is fundamental to their welfare.

Primates are important species for biomedical research and ensuring their good welfare is critical for research translatability and ethical responsibility. Systematic animal welfare assessments can support continuous programme improvements and build institutional awareness of areas requiring more attention. A multi-facility, collaborative project aimed to develop and implement a novel primate welfare assessment tool (PWAT) for use with research macaques. PWAT development involved: establishing an internal focus group of primate subject matter experts, identifying animal welfare categories and descriptors based on literature review, developing a preliminary tool, beta-testing the tool to ensure practicality and final consensus on descriptors, finalising the tool in a database with semi-automated data analysis, and delivering the tool to 13 sites across four countries. The tool uses input- and outcome-based measures from six categories: physical, behavioural, training, environmental, procedural, and culture of care. The final tool has 133 descriptors weighted based upon welfare impact, and is split into three forms for ease of use (room level, site level, and personnel interviews). The PWAT was trialled across facilities in March and September 2022 for benchmarking current macaque behavioural management programmes. The tool successfully distinguished strengths and challenges at the facility level and across sites. Following this benchmarking, the tool is being applied semi-annually to assess and monitor progress in behavioural management programmes. The development process of the PWAT demonstrates that evidence-based assessment tools can be developed through collaboration and consensus building, which are important for uptake and applicability, and ultimately for promoting global improvements in research macaque welfare.

The success of breeding primates in captivity has led to a surplus number of animals in collections. This review examines published journals and key books to investigate the various methods of primate population control. Hormonal, surgical and separation methods are discussed and evaluated with regards to behavioural and welfare implications. Methods of dealing with surplus animals are also reviewed. It is concluded that the successes of contraception methods vary significantly between species, and in some cases not enough is known to conclusively state that one method is preferable to another. The behavioural effects of contraception should be evaluated, as social status and sexual behaviours can be negatively affected by contraception. Non-reversible sterilisation methods, such as castration, should not be used without thorough evaluation due to the behavioural effects on the individual and group as a whole. Overall, the zoo community should share information of successes and failures of contraception in different species, and professional advice should be sought to ensure that the welfare of primates in captivity is not compromised.

Animal well-being and enrichment continue to gain importance in the maintenance of primates living in captivity. Positive reinforcement training (PRT) and/or playing interaction have been shown to be effective in improving the well-being of several species of primates. This research study evaluated the effects of applying a combination of these two techniques (training/playing therapy) on a group of lowland gorillas (Gorilla gorilla gorilla). The effects of this combination on the behaviour of captive primates have been given very little attention to date. The behaviour of a group of seven females was recorded in two different phases at Barcelona Zoo: before (periods 1 and 2) and after (periods 3 and 4) a series of changes were made to the composition of this social group. In each period, two phases were distinguished: i) baseline condition, after the subjects became used to the researcher, focal recordings were made of the group's regular behaviour and, ii) experimental condition, the training and playing sessions (‘gorilla play’) with two specific subjects began one hour before the group went to the outdoor facility. The frequency and duration of the behaviour observed in each of the recording conditions were compared. The results showed positive changes in the gorillas’ behaviour: stereotypies, interactions with the public, aggression between subjects and inactivity were all reduced, while affiliative behaviour and individual and social play-related behaviour increased. Moreover, the benefits of this therapy were observed in trained individuals and the rest of the gorillas in the group, which would seem to indicate that training/playing can be used to create a more relaxed atmosphere, reducing social tension and improving the well-being of all the subjects involved.

The COVID-19 pandemic led to unprecedented lockdowns with rippling impacts on the lives of humans and animals alike. Since zoos were among the first institutions to close during the pandemic, the lockdowns presented the opportunity to conduct a natural experiment examining the relationship between visitor presence and the welfare of zoo-housed animals. In this study, we assessed the welfare of six Sumatran orangutans (Pongo abelii) at Toronto Zoo both during and following the pandemic lockdowns. We compared behavioural and physiological indicators of welfare during a lockdown and after visitors were reintroduced. Specifically, if the orangutans’ welfare was affected by the visitor re-introduction phase we predicted there would be an increase in the following measures: (1) use of exhibit areas away from visitors; (2) behavioural measures (hiding, self-directed behaviours, agonistic behaviours, agitated movement, and idiosyncratic object-directed behaviours [head slamming, and fabric tearing]); and (3) physiological measures (faecal consistency and glucocorticoid metabolites) when compared to the lockdown. We also measured changes in activity levels such as foraging and inactivity. We found that orangutan exhibit space use did not change when visitors were reintroduced. In fact, the orangutans hid less when visitors were introduced than during the lockdown. Foraging, inactivity, and other behavioural indicators of stress did not change when visitors were introduced. Similarly, neither faecal consistency nor glucocorticoid metabolites changed across the study phases. Our data show that visitor re-introduction did not negatively affect the welfare of the Toronto Zoo orangutans. However, the presence of keepers was found to affect the behaviour of the orangutans and warrants further study.

Enrichment of the environments of captive primates is currently of interest as both a basic and an applied research question, particularly when social and inanimate enhancements are used simultaneously. We measured the behavioural effects of two intensities of inanimate enrichment on 12 unimale-multifemale groups and 12 all-male groups from three cohorts of three to four-year-old rhesus macaques (Macaca mulatta). Half of the groups received a simple, inexpensive enrichment programme while the other groups received a more complex and costly combination of physical andfeeding enhancements. Observations were conducted on 93 subadults of both sexes during their initial year of group housing. Intensity of enrichment did not differentially affect the amount of time subjects spent in any of the activities analysed. Subjects that received the more complex programme spent only 8.3 per cent of their time using the extra enhancements. Therefore, there was little demonstrated benefit of the more costly enrichment programme. The three cohorts differed in the amount of time that they spent inactive, behaving agonistically, playing and located near a group mate. A planned comparison of one cohort that had been single-housed without visual access to social groups, to the two cohorts that had visual access to social groups during single caging, revealed differences in play and socially-located behaviour, which may have been due to differences in extra-cage conditions two years prior to the present study. When primates are housed socially with conspecifics as ‘social enhancements ‘, the relatively simple inanimate enrichment programme we used was as effective as the more costly programme. When enrichment resources are limited, inanimate enrichment efforts should be focused on monkeys that are not socially enriched.

Training using positive reinforcement is increasingly recognised as a valuable tool for the humane and effective management and use of laboratory-housed non-human primates. We utilised a mixed-mode questionnaire to survey use of training and other learning processes (socialisation, habituation and desensitisation) in over half of UK establishments using and breeding primates. The survey demonstrated that there is widespread awareness of training as a refinement technique and appreciation of its diverse benefits, but training is not used as widely or as fully as it might be. This is due to real constraints (principally staff and time and a lack of confidence in ability to train), and perceived constraints (such as a supposed lack of published information on how to train and assessment of the benefits, and an overestimation of the time investment needed). There is also considerable variation between establishments in the purposes of training and techniques used, with a reliance on negative reinforcement in some. We conclude that there is opportunity for refinement of common scientific, veterinary and husbandry procedures (such as blood and urine collection, injection, capture from the group and weighing) through use of positive reinforcement training, especially when combined with appropriate socialisation, habituation and desensitisation. We end this paper with recommendations on best practice, training techniques and staff education.

For captive primates, environmental enrichment may improve psychological well-being, as indicated by changes in the frequency of species-typical and abnormal behaviours. The effects of enrichment on physical well-being have also been examined, but little attention has been devoted to the relationship between enrichment and animal health. We therefore studied the health records of 98 rhesus macaques (Macaca mulatta) to measure the effects that enrichment and social housing manipulations had on the number of veterinary treatments and days of therapy required by the monkeys. Subjects were housed singly, in pairs and in groups. Half of the subjects in each housing condition were enriched and the others were controls. Control and enriched subjects did not differ in the number of treatments they required, but enriched subjects received longer therapies than did controls. Neither treatments nor days of therapy were frequent or randomly distributed across housing conditions; pair-housed subjects required the least treatment and therapy, whereas singly-housed subjects were treated slightly more frequently for diarrhoea-related problems, and group-housed subjects for trauma-related problems. Subject age, however, was a potential confounding factor. Because subjects were part of a specific pathogen-free breeding programme, they spent only certain ages in each housing condition. Results suggest that inanimate enrichment neither diminishes nor improves the health of young macaques, but that enriched monkeys may require longer periods of therapy than do controls. Pair housing may be an effective housing strategy from both veterinary and behavioural points of view, necessitating relatively few treatments, but providing some social enrichment opportunities.

Human evaluation of animal emotional expressivity can inform animal welfare. Qualitative Behavioural Assessment (QBA) has been applied to domesticated and some non-domesticated animals, but its use in primates is limited despite their emotional expressivity. We aimed to develop and apply a QBA for bonobos (Pan paniscus) through two consecutive studies. We applied Free Choice Profiling (FCP) and the Fixed List methodology, respectively, in Study 1 and 2, and invited students and bonobo experts to rate video clips of zoo-living bonobos of different sexes and age classes, and before and after moving to a new enclosure. In Study 1, students described dimension 1 as ranging from ‘quiet/calm’ to ‘angry/active’ and dimension 2 from ‘sad/anxious’ to ‘happy/loving’. Experts described dimension 1 ranging from ‘quiet/relaxed’ to ‘nervous/alert’ and dimension 2 from ‘nervous/bored’ to ‘playful/happy’. Using a fixed list of descriptors, informed by findings from Study 1, students in Study 2 described dimension 1 as ranging from ‘quiet/calm’ to ‘agitated/frustrated’, and dimension 2 from ‘sad/stressed’ to ‘happy/positively engaged’. Experts described dimension 1 as ranging from ‘quiet/calm’ to ‘active/excited’, and dimension 2 from ‘sad/bored’ to ‘happy/positively engaged’. Students scored adults as more ‘calm/quiet’ and experts scored subadults as more ‘happy/positively engaged’. Additionally, experts in Study 2 rated bonobos as more ‘active/excited’ in their new enclosure. Reliability was moderate to good for the dimensions. Additionally, animal-directed empathy of observers influenced QBA scores. This is the first time, FCP has been successfully used as a method to study primate emotional expressivity. Our findings show the promise of employing QBA in primate studies and in industry, with validation of additional metrics to enable its use for welfare-monitoring purposes.

The provisioning of foraging opportunities to primates has been shown to be an effective means of enriching the laboratory environment. In this study artificial turf was used as the substrate for a particulate food given to the subjects as an environmental enrichment technique. Eight rhesus monkeys exhibited a significant reduction in behavioural pathology when allowed to extend the amount of time they spent in consummatory activities. An increasing trend in time spent foraging with a concomitant decline in aberrant behaviour over a period of six months was particularly noteworthy. No significant difference in preference for particulate monkey chow or more flavourful particulate food treats was expressed by the primates.

Good welfare is of inherent value to all captive animals and promotes species conservation objectives. Concern for animal welfare is growing globally, and research shows that animal welfare is a top priority for zoo visitors. There is, therefore, an urgent need for zoos to develop and validate species-specific welfare assessment tools with a shift in focus away from avoiding negative affective states, and towards promoting positive ones. This shift in emphasis requires the development of comprehensive and robust welfare assessment protocols incorporating species-specific indicators. This study aimed to identify and propose welfare indicators for captive chimpanzees (Pan troglodytes) that could be used to adapt the EU Welfare Quality® protocol for this species. A literature review was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines and the authors followed the principles of a systematic review to identify a comprehensive set of welfare indicators for this species. Overall, 14 animal-based and 16 resource-based indicators are proposed to assess the 12 criteria and four principles of Welfare Quality®. This study represents the first effort to adapt the EU Welfare Quality® protocol to assess captive chimpanzee welfare and illustrates how this protocol can be adapted to develop a taxon-specific welfare assessment tool once species-specific natural history and biology are considered.

Primates are bred in captivity for a number of purposes, from zoo-based captive breeding programmes for conservation to breeding for biomedical research. In each case, breeding animals that are fit for purpose, either as viable candidates for reintroduction or as valid research models, has presented challenges and resulted in steep learning curves. The breeding of animals for biomedical research has become increasingly focused on the production of animals that are less stressed by captive (specifically laboratory) environments. This is because elevated, particularly chronic, stress responses can result in altered physiological, neurological and behavioural states that have the potential to compromise the validity of scientific results. Selective breeding in captivity to, for example, maximise production, select for docile temperament or specific genotypes for biomedical research, is likely to be counter to natural selective pressures for evolutionary fitness. Given that many natural selective pressures active in the wild are absent in captivity, this paper reviews the selective breeding of primates (especially Old World monkeys) in captivity, its potential negative effects, and options that exist for ameliorating these negative effects.

Environmental enrichment programmes are widely used to improve welfare of captive and laboratory animals, especially non-human primates. Monitoring enrichment use over time is crucial, as animals may habituate and reduce their interaction with it. In this study we aimed to monitor the interaction with enrichment items in groups of rhesus macaques (Macaca mulatta), each consisting of an average of ten individuals, living in a breeding colony. To streamline the time-intensive task of assessing enrichment programmes we automated the evaluation process by using machine learning technologies. We built two computer vision-based pipelines to evaluate monkeys’ interactions with different enrichment items: a white drum containing raisins and a non-food-based puzzle. The first pipeline analyses the usage of enrichment items in nine groups, both when it contains food and when it is empty. The second pipeline counts the number of monkeys interacting with a puzzle across twelve groups. The data derived from the two pipelines reveal that the macaques consistently express interest in the food-based white drum enrichment, even several months after its introduction. The puzzle enrichment was monitored for one month, showing a gradual decline in interaction over time. These pipelines are valuable for assessing enrichment by minimising the time spent on animal observation and data analysis; this study demonstrates that automated methods can consistently monitor macaque engagement with enrichments, systematically tracking habituation responses and long-term effectiveness. Such advancements have significant implications for enhancing animal welfare, enabling the discontinuation of ineffective enrichments and the adaptation of enrichment plans to meet the animals’ needs.

Techniques to reduce or prevent behavioural disturbances in singly caged primates vary in form and effectiveness, with some behaviours being exceptionally resistant to treatment. Seven singly caged adolescent male olive hybrid baboons (Papio hamadryas anubis) were selected for behavioural intervention because of their severe abnormal behaviour. A continuous, all-occurrence sampling method yielded mean durations of abnormal and normal behaviour throughout the 10-week study. Analysis of baseline behaviour verified substantial durations of abnormal behaviour (mean = 9.80 min per 30-min observation period). We tested the effectiveness of four enrichment techniques: positive reinforcement training (PRT), food enrichment, non-food enrichment, and social enrichment (pair/trio housing). Each of the four enrichment conditions was implemented for a two-week period, with 10 30-min observations conducted per subject. We used repeated-measures analysis of variance to examine differences in behaviour durations between baseline and each enrichment condition. The social enrichment condition resulted in the most positive behavioural changes, including increased social behaviour and near elimination of abnormal behaviours (mean = 0.69 min per 30-min observation). Significant reductions in total abnormal behaviour levels were also found for other types of enrichment, but only social enrichment and PRT were effective in reducing whole-body stereotypies. Cage-directed and self-directed behaviours significantly decreased, whereas activity levels significantly increased during all enrichment conditions. The results of this project indicate that animate enrichment (human or conspecific stimulation), as opposed to inanimate enrichment, provides optimal means of behaviour modification for singly caged baboons. These findings have substantial implications for the welfare of captive primates in promoting successful therapeutic approaches for the behavioural management of laboratory primate species and for allocating limited enrichment resources.

Wild orangutans (Pongo spp.) rescued from human-wildlife conflict must be adequately rehabilitated before being returned to the wild. It is essential that released orangutans are able to cope with stressful challenges such as food scarcity, navigating unfamiliar environments, and regaining independence from human support. Although practical skills are taught to orangutans in rehabilitation centres, post-release survival rates are low. Psychological resilience, or the ability to ‘bounce back’ from stress, may be a key missing piece of the puzzle. However, there is very little knowledge about species-appropriate interventions which could help captive orangutans increase resilience to stress. This scoping review summarises and critically analyses existing human and non-human animal resilience literature and provides suggestions for the development of interventions for orangutans in rehabilitation. Three scientific databases were searched in 2021 and 2023, resulting in 63 human studies and 266 non-human animal studies. The first section brings together human resilience interventions, identifying common themes and assessing the applicability of human interventions to orangutans in rehabilitation. The second section groups animal interventions into categories of direct stress, separation stress, environmental conditions, social stress, and exercise. In each category, interventions are critically analysed to evaluate their potential for orangutans in rehabilitation. The results show that mild and manageable forms of intervention have the greatest potential benefit with the least amount of risk. The study concludes by emphasising the need for further investigation and experimentation, to develop appropriate interventions and measure their effect on the post-release survival rate of orangutans.

Given the difficulties of conducting regular endocrine and veterinary assessments of animals, behavioural observations are often the most commonly used tool to assess the welfare of animals in human care. Behavioural measures, inexpensive and convenient to collect, also have their challenges, such as ensuring the behaviours of interest are reliable indicators of an animal's internal state. Welfare assessments include both positive and negative indicators, and a commonly used indicator of negative welfare is self-directed behaviour (SDB). SDB has been described as a behavioural indicator of stress through observation and experimentation; however, this pattern is not universal despite assumptions otherwise. The purpose of this study was to experimentally evaluate the use of SDB as an indicator of negative welfare in mandrills (Mandrillus sphinx) with the goal of understanding the function of SDB in relation to stress. Using a touchscreen-mediated cognitive task, the mandrills were observed to self-scratch significantly more often during incorrect than correct trials; however, rates of SDB did not vary between increasingly difficult testing conditions. The mandrills had individual variation in their use of body-shakes and yawns under negative and positive conditions that mirror similar variation observed in other primates. This study provides experimental evidence that self-scratching in mandrills can be used as a behavioural indicator of anxiety and that welfare assessments for animals in human care need to account not only for species’ differences, but also for individual differences.

Visitors to zoos can be a potential source of stress to captive-housed primates, resulting in increased abnormal behaviour and intra-group aggression. Finding a way to screen primates from human visitors may be one method of decreasing stress and enhancing animal welfare. For this study, the behaviour of six zoo-housed gorillas was studied for one month during standard housing conditions (control condition) and for a further month following the installation of a camouflage net barrier to the viewing area of the exhibit (barrier condition). Visitors’ (n = 200) perceptions of the animals and the exhibit were also recorded during each condition. The net barrier had a significant effect on some components of the gorillas’ behaviour. The gorillas exhibited significantly lower levels of conspecific-directed aggression and stereotypic behaviours during the barrier than the control condition. The net barrier also had a slight effect on visitors’ perceptions both of the animals and of their exhibit. The gorillas were considered to look more exciting and less aggressive during the barrier than the control condition. The exhibit was also considered to be more appropriate for visitors following the introduction of the camouflage netting. Overall, the addition of a screen such as camouflage netting could be considered a positive change, resulting in a reduction in those behaviours typically induced by large groups of visitors and an improvement in public perceptions of the animals and their environment.

Regurgitation and reingestion (R/R) of foodstuffs is a common abnormal behaviour in captive western lowland gorillas (Gorilla gorilla gorilla) and certain other non-human primates, but it is not part of their normal feeding mechanism. It is similar to a behavioural problem seen in humans, human rumination syndrome (HRS), which can occur in association with anxiety or a poor relationship with a caregiver. Patients with HRS often regurgitate stomach acid with the food matter which can result in clinical problems; until this study, it was not known if stomach acid is regurgitated by gorillas also. Thus, samples of regurgitated matter were collected opportunistically and non-invasively, and pH was measured using an electronic meter. Results were compared with the pH of samples of the original food eaten by the gorillas, and show that regurgitated food has significantly higher acidity than the originally-ingested meal. By comparison, samples of saliva were collected from gorillas opportunistically, in the absence of recent ingestion, and were found to be alkaline and, thus, saliva should not have contributed to the increased acidity of regurgitated matter. The results imply that stomach acid is being regurgitated, as in human patients with potentially-injurious rumination syndrome, and it is indicative of sub-optimal welfare. Causes and effects of R/R should be investigated further, to lead to potential treatment and prevention and to promote the welfare of captive gorillas.

Abnormal behaviour in captive animals is both pervasive and ambiguous. Although individual differences are central to the field of animal welfare, studies on abnormal behaviour predominantly employ quantitative, population-level approaches. For example, whereas previous studies on chimpanzee (Pan troglodytes) abnormal behaviour have reported significant variation between groups or individuals in the quantity (eg frequency and duration) of abnormal behaviour, much less is known about qualitative differences. Individual abnormal behavioural repertoires may be highly idiosyncratic, where certain behaviours are over-represented (ie individually specific abnormal behavioural ‘signatures’). The present study investigated qualitative individual variation in the abnormal behaviour of chimpanzees (n = 15) housed at Royal Burgers’ Zoo in Arnhem, The Netherlands. Substantial variation was found between individuals in the diversity (size and evenness) and overall composition of their abnormal behavioural repertoires. Factors including age, sex, and rank did not significantly account for dissimilarity of individuals’ abnormal behavioural repertoires, but kin dyads showed more similar abnormal behaviour than non-kin dyads. Further exploratory analyses examined whether individual variation in one abnormal behaviour (coprophagy) predicted variation in stress-related behaviour (self-scratching). This allowed us to tentatively conclude that there were also individual differences in the link between a given abnormal behaviour and the behavioural expression of stress. Qualitative individual variation in abnormal behaviour provides a novel angle to a literature traditionally focused on quantifying abnormal behaviour at the group- or species-level and may thus represent an important yet previously overlooked source of variation in the extent to which abnormal behaviour reflects the state of individual welfare.