Nonhuman Primates: A Life in Captivity - Research by Francie Saunders
- francie saunders
- Aug 17, 2020
- 19 min read

Nonhuman primates have been a main focus of biological research in the laboratory and the field for decades. The biomedical research and its results have provided benefits for the human society that might not have been possible without the use of nonhuman primates, or NHPs. In the laboratory research setting, NHPs are captive animals subject to the actions of the humans conducting the research. They are most often housed in indoor cages and exposed to a life drastically different than the life of their wild conspecifics. Captivity’s effect on the behavior, genetics, and welfare of NHPs raise many ethical and scientific questions. The extent of the effects of captivity on the physiological and psychological wellbeing of NHPs are essential when considering the genetic similarities as well as the cognitive and emotional abilities of NHPs that are shared with humans. NHP intelligence has evolved to allow reasoning, planning, problem solving, and learning (Reader, Hager, & Laland) and their capability to experience emotions must not be disregarded. The most common species utilized in studies is the species macaque (Humane Society, 2009), and so will be the primary focus species of this paper. Utilized for breeding and biomedical purposes, thousands of macaques are subject to the environments of captivity that have been shown, in countless studies, to cause alterations in behavior, genes, and wellbeing that pose a concern for the welfare of these animals. Although captivity may be used for conservation, rescue, or beneficial research efforts, its detrimental effects on animals suggest it should only be utilized for a brief amount of time in an environment that mimics natural wildlife while holding the ultimate goal of reintroduction to the wild.
Nonhuman Primates as Models for Humans
Macaques in captivity include, but are not limited to, the rhesus, cynomolgus, crab-eating, pig-tailed, and long-tailed macaques. Research on macaques has allowed for huge medical strides in the human society that would not have been capable without the use of NHPs as their inability to consent to and escape from captivity is preferable and seen as ethical in contrast to using humans. The benefits from macaque research include the vaccines of polio, rabies, and smallpox, and the development of drugs to aid in managing HIV and AIDS, and many other discoveries based in behavioral and biomedical research (Lang, 2010). As technology and science advances, NHPs are strongly relied on for organ transplants “as artificial organs generated in NHPs have similar sizes as those of humans” and can benefit humans more than other animals’ as NHP’s organs are “likely to cause less immune rejection” in humans (Zhou, 2014). The similarities of humans and nonhuman primates range from the category of cognition and brain structure to the expression of emotions and behaviors. NHPs function as such valuable models for humans because of the many similarities we share such as a “prolonged developmental period, higher cognitive processing, complex social interactions, a more diversified behavioral repertoire” and we are closely evolutionarily related (Lutz, 2014). In fact, the difference between the DNA of humans and chimpanzees (another NHP commonly used in research) is “only slightly higher than 1%” (Zhou 2014). This relationship further brings into question the ethics of NHPs in captivity. Stereotypies performed by humans and NHPs coincide as both eye poking, hair pulling, rocking, and pacing have been observed in both species. Yet, in spite of these parallels, we sometimes overlook the stressful and painful situations permitted that elicit perceivable signals of distress in NHPs. Unfortunately most research on NHPs involves invasive and painful procedures for the animals as well as a stressful life in captivity. The ethical debate of nonhuman primate research has persisted for years and brought greater attention to the lives of animals in captivity. Throughout the decades of gaining from NHP research, it has become a great concern to maintain a positive wellbeing for the captive animals in order to promote healthy psychological and physical welfare.
Metrics of Nonhuman Primate Wellbeing
Measuring the welfare of a primate that cannot communicate its internal workings to humans is extremely challenging, as the appropriate metrics are unclear and varied. Hypothalamic-pituitary-adrenal activation, corticosteroid levels, gastric ulceration, and anorexia are physiological factors that have been used as means to observe and measure levels of stress in captive animals (Basset & Buchanan-Smith, 2006). The production of corticosteroids for an extended period of time in an animal under stress can have detrimental effects to its wellbeing through strong suppression of the immune system. Whereas these hormones can provide benefits to the animal in relatively small doses, if an animal is subject to these hormones for a longer time it can suffer from a “delay of puberty, suppression of growth, metabolic exhaustion,” and an “increased susceptibility to disease and neuron death in the hippocampus” (Basset & Buchanan-Smith, 2006). While these are some physiological methods of measuring welfare, other metrics dealing with behavior have been proven to supply humans with important information about captive animals.
Abnormal Behaviors Provide Insight into the Captive Experience
The presence of stereotypies, abnormal behaviors, motor stereotypic behaviors, and self-injurious behaviors have afforded insight into the wellbeing of NHPs in captivity and promoted an active consideration by researchers and policymakers to improve captive life. Marian Dawkins addresses the stigma associated with the scientific consideration of other animal’s “feeling” and “emotions” by arguing that we as humans do not “have to choose between scientific respectability and practical considerations” (Dawkins, 1990) when understanding the experiences of animals in captivity. As science has rapidly progressed, further research and interest into the subjective feelings of nonhuman animals has realized their capability to experience suffering. Dawkins reminds those interested in measuring and studying captive animal welfare that the point of view of animals must be considered “in all animal welfare studies because it provides the only plausible bridge between observable events such as physiological and behavioral changes” with “the subjective experiences of animals” (Dawkins, 1990). When considering the physical, psychological, and behavioral wellbeing of NHPs in captivity one must recognize the significant link between the animal’s internal state and its outward expressions.
Ability to Suffer
When studying and considering the internal state of nonhuman primates, it is important to avoid imposing an anthropomorphic view on the issue, and instead remain objective, despite the many similarities shared among humans and NHPs. Avoiding this bias is important, but recognizing the capability of animals to suffer and to have unpleasant experiences is also vital in terms of ethics and in understanding a species. The modes humans use to define feelings, emotions, and sensations may differ greatly from how they are experienced in other species, but these experiences may for all species “have evolved by natural selection as a means of avoiding danger or restoring physiological deficits” (Dawkins, 1990). NHPs in captivity are typically deprived of performing tasks they would naturally accomplish in the wild. The behaviors the animal desires to perform may not serve the same purpose in captivity as they would in the wild, but even so being deprived of the behavioral opportunity may cause the individual to suffer. Behaviors like foraging may not be necessary for captive NHPs, as humans provide food, and therefore there is no “canonical cost,” or ultimate cost, for not performing the behavior as there is in the wild (Dawkins, 1990). Even so, an animal in captivity deprived of expressing a behavior that would normally increase fitness may still react as if failing to perform would result in death or harm, and in turn the animal may suffer greatly from this deprivation. Although suffering in NHPs is not completely understood, abnormal and sometimes even self-harming behaviors have been proven to accurately assess psychological wellbeing.
Causes of Abnormal Behaviors
The abnormal behaviors observed in captive NHPs often suggest poor welfare and can be influenced by many aspects of a captive environment such as rearing history, individual temperament, stress and frustration, boredom, housing type, and are often mechanisms performed by the animal to cope with their unnatural experience of life in captivity (Gottlieb, Maier & Coleman, 2015; Lutz, Davis & Ruggiero, 2007; Coleman, 2011). The abnormal behaviors commonly observed in captive rhesus macaques can have a range of expressions and causes. In their study Bayne and Novak (1998) concluded that abnormal behaviors are “considered pathological in nonhuman primates if it occupies a substantial portion of the animal’s time budget, interferes with biological functions, or induces tissue damage” (Lutz, 2014). Stereotypies, a common behavior found in captive rhesus macaques, are repetitive behaviors often brought on in animals “by central nervous system dysfunction, frustration, or repeated attempts to cope” and are common indicators of stress (Mason, 2006). It is also important to recognize that the lack of abnormal behavior does not imply that an animal is in a healthy mindset as individuals can respond to different situations in many different ways according to their specific temperament.
Depression and Inactivity
NHPs in captivity can also fall victim to depression, or what is recognized as depression-like symptoms as seen in humans, and in turn adopt an inactive lifestyle compared to others in captivity and especially their wild counterparts (Camus, Rochais, Blois-Heulin, Li, Hausberger & Erwan, 2014). A study that observed rhesus macaques found that those categorized as “depressive-like” weighed less than average, avoided interacting with peers, faced the walls of their enclosure, spent most of their time in an inactive state devoid of locomotive behaviors, and lost interest in the usual activities expressed in the time budgets of wild macaques (Camus et al., 2014). These results highlight an important matter when measuring welfare of captive NHPs as individuals who do not perform abnormal or harmful behaviors might be generally inactive due to depression brought on by the suboptimal environment and could still in fact be suffering.
Rearing History
Rearing history plays a large role in predicting the onset of self-injurious and abnormal behaviors in macaques and other captive species. When NHPs are born in facilities, rearing plans determine how to raise the individual. One study found that the most accurate predictor of stereotypies and self-injurious behavior is an “impoverished early rearing experience” imposed by captivity (Lutz, Well & Novak, 2003). An impoverished rearing experience refers to an early life that lacks interaction with a mother and companionship with conspecifics. Just as abnormal behaviors can be predicted by rearing history in NHPs, humans raised in poor living conditions or isolation commonly perform stereotypies (Lutz, 2014). For example, humans that were born and then raised in poor orphanages or group homes developed stereotypic behaviors. On the other hand, children in foster homes showed less stereotypy compared to their orphan counterparts (Lutz, 2014). Research by Gottlieb et al. (2013) analyzed the effects of rearing history on individuals at the California National Primate Research Center. The rearing conditions varied by isolation or partial isolation, with aspects of indoor and outdoor captivity. Isolated rearing is less commonly utilized and instead partial isolation, which can be referred to as mother-reared or nursery-reared, is more often employed. Mother rearing occurred indoors or outdoors and both had varying influences on the infant’s behavior. When indoors, mother rearing and nursery-rearing occur without a social group, and at most include another pair of mother and offspring (Gottlieb, Capitanio & McCowan, 2013). In the wild, rhesus macaques “lead highly sociable lives” (McGrew, 1981) as the species has evolved to learn from birth from their family and conspecifics about what predators and foods are, how to behave socially, and other ways to increase fitness. Although mother rearing involves a biological or surrogate mother with the young macaque, this method greatly deprives both individuals of important social interaction inherent to the species (Gottlieb et al., 2013). Nursery-reared animals are “separated from their mother at birth and individually housed” for the first few weeks of life (Gottlieb et al., 2013). After being separated from its mother, both infant rhesus and cynomologus macaques were observed to enter a “despair-like state” and perform higher rates of “locomotion, vocalization, and defecation,” which could be indicative of stress and suffering in the individual (Camus, Rochais, Blois-Heulin, Li, Hausberger & Erwan, 2014).
These individuals, like countless others, are born with the innate need to be mothered and cared for, and without this it is unsurprising that their welfare would be negatively affected. Following three weeks of isolation, the young are then provided with only visual access to a similarly aged conspecific that they will then be paired with two weeks later (Gottlieb et al., 2013). In this study, the nursery- or indoor mother-reared individuals were found to express higher rates of abnormal behavior and bite their self more than conspecifics reared in field cages (Gottlieb et al., 2013). Relative to indoor cages, field cages are larger with more opportunities to explore surroundings and express natural social and foraging behaviors. Individuals reared in field cages were outside with their mother and a number of other conspecifics (Gottlieb et al., 2103).
The natural behaviors that have evolved from complex societies, interactions with the environment, and the desire to share in the company of others are obstructed by the use of indoor mother and nursery rearing. Mothers and offspring are deprived of greater companionship and forced to live in isolated and movement-limiting cages. The effects of early experience with limited social interaction and small cage size “may be the most salient predictors of” abnormal and harmful behaviors (Gottlieb et al., 2013). These early experiences function as an important tool in determining the best life for a captive NHP, and housing type in general can also predict the performance of abnormal behaviors.
Housing
As addressed above, housing type and social contact play essential roles in the wellbeing of captive macaques. As NHPs like the rhesus macaques are social beings and have undergone evolution to live in complex societies, “the ability to engage in social interactions is critical for normal development,” (Coleman, 2011) as it is for humans. Various housing types have drastically different effects on the behaviors of rhesus macaques and can be in form of individual, grate-pair, paired, or social housing. The performance of stereotypies as well as self-injurious behavior by captive macaques “are aberrant and potentially destructive patters of behavior” that are not only reported in NHPs but humans as well (Lutz, Well & Novak, 2003). Macaques housed individually live in traditional single lab cages measuring 0.62 x 0.36 x 0.73 m, can only see and hear other macaques, and one study of 362 rhesus macaques found that at least 89% of these NHPs performed abnormal behaviors (Lutz et al., 2003). Results found that hair pulling, eye or face poking, self biting, and self injurious behaviors had a positive correlation to the amount of time a macaque was in individual housing (Lutz et al., 2003). This study suggests that employing isolated housing later in life can decrease the rate of abnormal behaviors, but simply aiming to decrease these behaviors and adverse experiences is not enough. Grate-pair housing has often been implemented to improve the experience of individual housing. In this type of housing two cages are joined by a divider that allows a NHP to see and hear as well as obtain “limited physical contact with their neighboring animal” (Gottlieb, Capitanio & McCowan 2013) by sticking an arm through the divider. Contrary to efforts, a study found that grate-pair housing actually produced “levels of abnormal and tension-related behaviors” significantly similar to what was seen in individually housed macaques (Gottlieb et al., 2013). On the other hand, paired-housing where animals share two cages and have full contact with each other was recently found to have a negative correlation with the expression of stereotypic behaviors in rhesus macaques (Gottlieb, Maier & Coleman 2015). Outdoor social housing has found to ultimately be the best housing type to reduce the expression of self-injurious and abnormal behaviors in captive rhesus macaques. Living with multiple other conspecifics provides “crucial social and environmental stimulation to promote proper development” for most, if not all, NHPs (Gottlieb, Capitanio & McCowan 2013). Housing of NHPs, like macaques, can also be improved through non-social stimulation referred to as enrichment.
Environmental Stimulation and Temperament
Laboratory environments inherently lack stimulation. Small and artificial enclosures limit the movements and activities of NHPs. NHP evolution is in part a result of a “sophisticated relationship to the environment” that can be seen in the time budget of rhesus macaques that spend a majority of their time in the wild foraging for food (Cunningham & Janson 2007; Gottlieb, Maier & Coleman, 2015) and associating with conspecifics. An enriched environment is not only in the interest of captive individuals, but any research that relies on NHP processes “will be enhanced in direct proportion to the resemblance of conditions in captivity to those in nature,” as a natural environment would limit confounding variables like abnormal behaviors and produce the most accurate results for research (McGrew, 1981). Anxiety is a common outcome of a suboptimal environment that does not allow an animal to express desired behaviors and is often correlated with the development of stereotypies or self-injurious behavior. Enhanced by stressful situations, anxiety can coincide with “the development of clinical and behavioral problems” as well as depression in both humans and NHPs (Coleman & Pierre, 2014). Contrary to what one may assume, it may be observed that a macaque performing abnormal behaviors is perceived to be in good health. This can be explained when the animal, as a means to cope with the imperfect environment and improve its own welfare, performs these behaviors (Lutz, 2014). On the other hand, if an individual is in a situation where it has to find ways to cope with its environment, this signals an unsatisfactory, and most likely inhumane, quality of life. Methods with which humans have generally had success in reducing stereotypic behaviors in captive NHPs include canine companionship, social interactions, foraging opportunities, larger cage size, toys, and life outdoors (Lutz, 2014). The ultimate aim of enrichment is for a monkey to partake in activities that reduce stress and require a behavior that is incompatible with abnormal and harmful behaviors (Gottlieb, Maier & Coleman, 2015). A psychological wellbeing considered to be positive and healthy is reinforced through the choice and control an animal has in its environment through engaging enrichment practices (Coleman, 2011). But when introducing a form of enrichment to a captive animal, the NHP’s individual temperament must be carefully considered in order to avoid increasing stress or anxiety for the monkey.
All aspects of captivity, and therefore any environmental changes to improve captivity, can elicit different responses from an individual given its personality or temperament. Temperament is intrinsic to each individual NHP and can arise in an animal’s earliest years to persist throughout its lifetime (Coleman, 2011). In humans, temperament has been found to have an affect on health, such as life span, and to have similar implications in rhesus macaques and other NHPs (Coleman, 2011). When pairing individuals in captivity it is important to find compatible relationships that will in turn benefit the NHPs by reducing stress and providing companionship. Although social housing is preferable to paired in most cases, when pairings of adult monkeys were examined, it was found that the successful pairs were between monkeys whose temperaments were similar in terms of inhibition, reactivity, and activeness (Coleman, 2011). Being able to assess an individual’s temperament can provide advantageous insight when determining the most successful methods of housing and enrichment to employ. An individual that is usually nervous and anxious in response to environmental changes may suffer greatly from common husbandry practices in relation to its counterpart that may be less inhibited and able to cope with change in healthier manners. The importance of the individual cannot be understated, especially when understanding how to generate success in the reintroduction of captive animals to the wild.
Beneficial Practices of Captivity
The harmful effects of captivity on NHPs, and undoubtedly on other captive animals, cannot be ignored and insist a change in attitude towards the use of these creatures in research. As climate change and human activity reduce habitats and threaten the existence of species, conservation rises to center stage. Natural environments are destroyed everyday leaving tiny fragments of habitats in which animals must find success in survival and reproduction. Because of the devastating effects of human actions on other species, captive breeding has found to be of great use to conservationists trying to restore populations. In this sense, as a means to protect species from outside threats, captivity can be justified. Only so if it is utilized for brief periods, mimics natural environments, encourages normal behaviors, and has the goal of prompt reintroduction for those capable. Then, captivity can serve to benefit nonhuman primates.
Reintroduction
Brevity is essential in reintroduction as extended time in captivity can result in behavioral and genetic changes that may be detrimental to the survival of the animal and the resulting population. Britt and colleagues went so far to say that those born in captivity are experiencing something “comparable to the early stages of domestication,” which would serve greatly to impede a monkey’s success in a natural habitat (Britt, Welch & Katz 2003). Selective pressures enforced by aspects of captivity can have a direct affect on an animal’s temperament and in turn its fitness.
Those animals that are more active or display aggressively most often do not fare well in captivity although these traits may be useful in the wild. Not only are new selective forces of concern but also the “relaxation of natural selection can result in the persistence of behavioural traits and deleterious genes that are selected against in the wild,” resulting in individuals, and even populations, that are unfit to survive if reintroduced (McDougall, Réale, Sol & Reader, 2005). Programs that aim to reintroduce individuals are, and should be, cautious to avoid artificial selection. Despite this, humans can unconsciously create a selective force through the activities and interactions with the animals that take place in captivity (McDougall et al., 2005). When dealing with captive animals and daily husbandry activities, a researcher may prefer to work with an animal that is calm and cooperative, but in turn this preference may “inadvertently lead to selection by increasing stress levels” in an individual who cannot remain calm or find ways to cope (McDougall et al., 2005). The less time the monkeys spend in captivity, the less likely that selective forces will have a major effect on the genetic composition and behavioral tendencies of individuals.
Macaques bound for reintroduction must possess the sufficient traits and behaviors that will promote their success in the wild. Effective programs would employ the practice of training the monkeys “to cope with specific challenges” that will be faced in their new environment including social situations, foraging behaviors, how to avoid predators, and exploring new environments (McDougall et al., 2005). Without environments that mimic what will be encountered in the wild, macaques will not be able to express this array of natural behaviors and may even lose capabilities the animals were born with if they cannot be performed in the captive setting (Britt, Welch & Katz 2003).
Many studies that reintroduced captive animals into the wild without any proper training witnessed high mortality rates and brought attention to probability that most of the traits needed in order to survive are learned in early development and absent in captivity (Britt et al., 2003). A study of the release of lemurs into the wild found that when individuals died it was most commonly a result of predation, suggesting that the knowledge to avoid a certain predator is learned from conspecifics in the wild (Britt et al., 2003). The researchers recommended their tactic of utilizing muzzled dogs in the natural, yet captive, environment to encourage anti-predator behavior as well as implementing a “soft release” in terms of reintroduction. This includes providing food if the monkeys are underweight or having trouble foraging and recapturing animals or providing veterinary care if necessary (Britt et al., 2003). But most importantly they stress the use of “rapid integration” of captive individuals into the wild as this promotes the essential experience of learning “vital survival skills from their wild conspecifics” in order to acclimate and survive (Britt et al., 2003).
The innate sociability and the critical learned experiences from kin and companions during development are highlighted continuously when addressing what captivity deprives from NHPs. With captivity serving only to restore communities and populations so as to benefit NHP species we can restore the welfare and balance of individuals in the wild.
Analysis
The use of NHPs in research has undoubtedly been the reason for many scientific breakthroughs over the decades, but at what cost to the animals involved? Most often, from birth, individuals are forced to live alone in cages with the chance of being able to see or hear others, but often not touch. Their social needs are impossible to fill in small cages lacking social interaction and environmental stimulation that is not stressful. This dramatically and detrimentally hinders their development, physiological and psychological.
As we continue to acknowledge the cognitive and emotional abilities, complex brain structure and intellect, essential societal relationships, and developmental similarities of NHPs with humans, I find it extremely difficult to justify the use of captive, nonhuman primates in research. We cannot assume that the existence and experiences of nonhuman animals are of lesser importance to our own simply because we do not completely understand what other creatures think or feel. We cannot assume that we know the extent to which other species experience life and instead we must embrace the fact that there is so much we do not know. Human beings have the power to make these dramatic changes and act to improve the lives of other species. I suggest that alternatives should be the aim and focus of all NHP biomedical research to deplete the number of animals in captivity. Research conducted by those interested in the behaviors and wellbeing of captive animals should only be retrospective analyses and should focus on ways to reduce the need to keep animals captive. The 3R principles, “which aim to replace and reduce the use of NHPs, and refine the related methodologies” and minimize the dependency of these animals in our research should be upheld by all those involved (Zhou, 2014).
The world’s technology and our knowledge of it are rapidly growing greater and stronger, giving biomedical research countless options into the use of computational modeling assistance instead of using NHPs (Zhou, 2014). Also, simply recognizing that some diseases or illnesses we are interested in are specific to the human genome and therefore the use of NHPs to further our knowledge is not only unjustifiable but also useless for those endeavors (Zhou, 2014). Research that is interested in improving or understanding the welfare of animals in captivity should instead redirect its focus and funds to discovering and improving alternate practices that provide what NHP research does without depriving these individuals of their life in the wild.
I acknowledge that this idea to abolish the use of NHPs in research and only utilize captivity for conservation, rescue, relocation, reintroduction, or restoration efforts might seem far-fetched and hopeful, but it is possible and there are alternatives to animals in research. Results from studies cited above, and countless unmentioned, unmistakably provide us with the evidence of the devastating effects of life in captivity to which thousands of creatures are subjected. As climate change, habitat destruction, extinction, global warming, and more continue to plague our planet we must combat all injustices to our fellow beings and our environment with fervor undeniable.
The behaviors displayed by those nonhuman primates in suboptimal living environments, reflected by those of our own species in similar situations, can serve as indicators wellbeing but more importantly they highlight the atrocity that is captivity. Instead the use of large, complex, social environments and training of natural species-specific behaviors, individuals have had great success not only in instances of captivity but also in the event of reintroduction. Invasive and stressful procedures performed by curious humans with countless personal objectives are forced upon these individuals. Perhaps those individuals respond by becoming unresponsive, harming their self, pacing, or developing an aggressive “personality,” in order to cope with what they experience. The relationship between not only humans and nonhuman primates, but also all living things, is extremely intertwined and undeniably beautiful. To deny other beings of their right to live a life free of the stress and pain caused by captivity is unjust. As scientists, intellectuals, and human beings we must see it as a personal priority to serve our species and all species with which we share this planet.
Bibliography
Basset, L. & Buchannan-Smith, H.M. (2006). Effects of predictability on the welfare of captive animals. Applied Animal Behaviour Science, 102, 223-245.
Britt, A., Welch C., & Katz A. (2003). Can small, isolated primate populations be effectively reinforced through the release of individuals from a captive population?. Biological Conservation, 115, 319-327.
Coleman, K. (2011) Individual differences in temperament and behavioral management practices for nonhuman primates. Applied Animal Behaviour Science, 137, 106-113.
Cunningham, E. & Janson, C. (2007). A socioecological perspective on primate cognition, past and present. Anim Cogn, 10, 273-281.
Gottlieb, D.H., Maier A. & Coleman K. (2015). Evaluation of environmental and intrinsic factors that contribute to stereotypic behavior in captive rhesus macaques (Macaca mulatta). Applied Animal Behaviour Science, 171, 184-191.
Humane Society. (2009, September 28). Questions and Answers about Monkeys used in Research. Retrieved 20 November 2015. http://www.humanesociety.org/animals/monkeys/qa/questions_answers.html?credit=web_id88069391#What_types_of_monkeys_are_most_frequentl
Lang, K. C. Primate Info Net. (2010, July 20). Rhesus Macaque Macaca mulatta. Retrieved 20 November 2015, from http://pin.primate.wisc.edu/factsheets/entry/rhesus_macaque
Mason, G. (2006) Stereotypic behaviour in captive animals: fundamentals and implications for welfare and beyond. In: Mason, G., Rushen, J. (Eds), Stereotypic Animal Behaviour: Fundamentals and Applications to Welfare (2, pp. 325-356). Wallingford: CABI.
McDougall, P.T., Réale, D., Sol, D., & Reader, S.M. (2006). Wildlife conservation and animals temperament: causes and consequences of evolutionary change for captive, reintroduced, and wild populations. Animal Conservation, 9, 39-48.
McGrew, W.C. (1981) Social and cognitive capabilities of nonhuman primates: Lessons from the wild to captivity. International Journal for the Study of Animal Problems, 2, 138-149.
Reader, S.M., Hager Y., Laland K.N. (2011). The evolution of primate general and cultural intelligence. Philosophical Transactions of the Royal Society, 366, 1017-1027.
Zhou, Q. (2014). Balancing the welfare: the use of non-human primates in research. Trends in Genetrics, 30, 476-478.
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