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The Behavioral Management Unit at the Yerkes National Primate Research Center oversees the nonhuman primate colony’s psychological well-being. The primates at Yerkes are housed in several different housing types including: single, panel housed (a perforated panel through which the monkeys can interact is between their two cages), in pairs and in groups. For the present study, data were collected, compiled and analyzed for 115 rhesus macaques (Macaca mulatta) who were housed singly or in pairs. Past research has shown social housing to be more beneficial than single housing, allowing a broader range of species typical behaviors. The current study upheld that conclusion, finding that socially housed animals exhibit significantly more pro-social behaviors and more object manipulation, a species typical behavior. These findings contribute to an expanding body of research evaluating housing types for nonhuman primates in the laboratory setting.
Ever since the Animal Welfare Act [1985] required provisions for the psychological well-being (PWB) of non-human primates, scientists have struggled to define precisely what PWB encompasses. Most would agree that providing opportunities and environments that increase species typical behavior and decrease abnormal behavior is a large component of providing for non-human primate well-being. Numerous studies have examined the behavioral effects of manipulating the environment of captive primates with the goal of improving their psychological well-being [Schapiro, Bloomsmith, Porter & Suarez, 1994; Baker, 1996]. Previous research has shown that the benefits of social housing are generally evident by increased expression of species-typical behaviors [Novak & Suomi, 1991] such as increased social grooming, playing, exploring and decreased time devoted to inactive and in abnormal behavior [Schapiro et al, 1994]. These are considered beneficial changes in behavior.
While a type of social housing called pair housing of rhesus monkeys is often used, in which monkeys share the space of two cages, another type of housing, referred to as single housing is sometimes necessary due to research needs.
Identifying the amount of species-typical behavior, as well as the amount of abnormal behavior exhibited in rhesus monkeys housed in pairs or individually is an important step in assessing the psychological well-being of the nonhuman primates at Yerkes. The Behavioral Management Unit at Yerkes has recently developed a computerized, quantitative behavioral assessment program and this system was applied to compare the behavioral repertoires of pair and individually housed rhesus monkeys.
Hypothesis
Monkeys housed in pairs will show more species-typical and pro-social behavior than those housed individually.
Singly housed monkeys will spend more time displaying abnormal, self- grooming, and anxiety related behaviors than those housed in pairs.
Monkeys housed in pairs will spend more time manipulating objects that singly housed monkeys.
Monkeys housed in pairs and singly will show no significant difference in amount of time spent feeding or displaying aggressive behavior.
Monkeys housed in pairs will spend more time using enrichment than singly housed monkeys.
Subjects: The rhesus monkey (Macaca mulatta) subjects were housed either singly (n=61) or in pairs (n=54). The subjects were between 3 and 24 years of age, with 77 male and 38 female subjects.
Data Collection:
Subjects were observed over a six week period using the Observer software package and an iPAQ handheld computer. Focal animal sampling using a behavioral ethogram previously developed by the Behavioral Management Unit was used. Interobserver reliability was maintained at over 85% agreement. Each monkey was observed on four separate occasions for five minutes per observation. Eighteen hours of pair housed data and 21 hours of individually housed data were collected. Data were collated from the Observer software, and transferred to an Excel spreadsheet. Using the SPSS version 17.0 software system, a series of Student t-tests were applied to look for behavioral differences in rhesus monkeys across the two housing conditions, and to test our hypotheses.
Statistics were performed to compare behavior across the two housing conditions, with the following behavioral categories being tested: abnormal behavior, anxiety, manipulation of objects, social behavior without contact, feeding, enrichment use, self grooming, pro-social behaviors (play with or without contact, non-aggressive behavior with or without contact, grooming), and aggressive behaviors. Using t-tests, we found statistically significant differences with more object manipulation and more pro-social behavior in pair-housed monkeys. In singly-housed monkeys we found significantly more self-grooming. Other categories tested did not show statistically significant differences.
The rhesus monkey (Macaca mulatta) is the most commonly used laboratory primate in the United States. For this reason, identifying the behaviors that are associated with different living housing options is useful for providing the most beneficial environment possible. The findings from this study are similar to a previous study [Schapiro et al, 1994] in the areas of self-grooming, feeding, and pro-social behaviors. However, the findings differ from the previous study [Schapiro et al, 1994] in the areas of abnormal behavior and enrichment use. The data suggests that the presence of a social partner is favorable. The pair housed animals studied spent more of their time manipulating objects and engaging in pro-social behaviors. Therefore, it is concluded that rhesus macaques should be provided with pair housing whenever possible, as these efforts to provide a social living environment for rhesus macaques will be beneficial to them.
Further Research
Future research could include studies that incorporate additional types of housing options such as panel housing and group housing to expand the comparisons made.
Figure 8. Group housed monkeys at play.
This material is based upon work supported by the Howard Hughes Medical Institute under Grant No.52005873 which supports the Summer Undergraduate Research Program at Emory University, and the Yerkes National Primate Research Center (YNPRC) Base Grant RR-00165 awarded by the National Center for Research Resources of the National Institutes of Health. YNPRC is accredited by the Association for the Assessment and Accreditation of Laboratory Animal Care International (AAALAC International).
Thank you to the Behavioral Management Staff at Yerkes. The help and expertise they supplied has been invaluable to this project.
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