Vervet Monkey Orphans Raised via Surrogacy and How Their Behaviors Differ from Those of Vervet Monkeys Born and Raised Biologically
Vervet monkeys (Chlorocebus pygerythrus), particularly infants, are winding up in rehabilitation centers all over Africa at an increasingly alarming rate because of habitat loss and human interference (Pillay et al. 2024). An ongoing challenge wildlife rehabilitators face is trying to give orphaned vervets a chance to be successfully released back into the wild. Orphaned vervets are especially hard to rehabilitate because the mother-infant bond is so vital to the individual’s development (Desbiolles 2007). Infants taken in have yet to learn survival skills and must be raised in the rehabilitation facility by humans. This, coupled with vervets’ complex social hierarchies, makes it difficult to prepare orphans for life in the wild.
The author, Morgan Breen, with a vervet monkey.
Surrogate mothers provide a great solution to these issues. Success has been found using surrogate mothers to raise orphans, teaching them proper survival and social skills (van Niekerk & Pillay 2023). Surrogate mothers are adult females being rehabilitated who are willing to accept and rear an orphaned individual as their own. These mothers are unable to be released because of their injuries. However, they still have their maternal instincts. Providing orphans with accepting surrogate mothers and continuous peer interactions with other individuals of the same age range can provide the best chance for successful social rehabilitation (Harlow & Suomi 1971).
Bambelela, meaning “to hold on” in Zulu, is a vervet monkey rehabilitation facility in Bela Bela, Limpopo, South Africa, that has adopted this practice. With the help of an International Research Opportunities Program (IROP) grant and my mentors, Silke Von Eynern, founder of Bambelela, and Dr. Andrew Conroy of the University of New Hampshire (UNH), I spent nine weeks studying the differences that arise when comparing vervets raised biologically with those raised with this surrogate method. In particular, I compared play behaviors/interactions and dominant behaviors/interactions between the two groups. I hypothesized that individuals raised biologically display more intraspecific dominant behaviors and partake in more play interactions than those raised by surrogates. Evaluating these behaviors provides valuable information to rehabilitators because it can help us determine how successful these surrogate mothers are at preparing orphans for release in the wild. My goal was to assess how to provide these orphaned monkeys with the best chance of survival post-release.
Complex Vervet Troop Dynamics, Most Common Threats, and Why They Matter
Currently, the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species has the vervet population in the category of “Least Concern.” However, their population trend is declining (Butynski & De Jong, IUCN Red List 2022). As Africa becomes more urbanized, vervet monkeys’ habitats are slowly diminishing. This has led to increased interactions with humans and the species being labeled as vermin. In South Africa, laws differ from province to province, but in Limpopo Province, a law passed in 2005 requires that people apply for a hunting permit to kill vervet monkeys. However, when vervets are mentioned as “problem-causing animals,” the permit to kill is easily obtained from the authorities.
A few infants in the Kindergarten Troop observing me as I cleaned the “Pink Face Room.” The pink face room is where the orphans are held once they can leave quarantine but are still too small to move into the full Kindergarten enclosure. They still have their pink faces at this stage.
As a result, vervet population sizes are dwindling because of hunting and pest control (Ramkissoon 2005). Vervets are commonly killed in retaliation for destroying crops, and hunted for bushmeat (African Wildlife Foundation 2019). Vervets are also confiscated as pets and abused by humans (Guy & Curnoe 2013; Healy & Nijman 2014). They are often stolen from the wild, typically by killing the mother and keeping her baby. Since they bite through every emotion (happy, sad, angry, excited) and are illegal to keep, they are then given up as pets, taken away by police, or have their teeth removed. Most vervets that wind up at rehabilitation facilities were pets reared by humans, making it a difficult process to rewild them away from human care.
It is critical to keep the wild population levels up, because vervet monkeys play a vital role in the ecosystem and many plant species rely on primates for seed dispersal (Andresen et al. 2018). They are responsible for controlling local bird and insect populations, maintaining predator population sizes, and aiding in the germination and pollination of local fauna. Their fruit-heavy diet allows for seeds in their excrement to repopulate many species of native trees, and many other animal species’ diets rely heavily on the presence of vervets (Bahr, New England Primate Conservancy 2021).
Vervet social hierarchies are matrilineal troops, or groups of monkeys that form based on the mothers’ kinship (Desbiolles 2007). These range from ten to forty monkeys per troop, depending on the environment (Bahr, New England Primate Conservancy 2021). Vervets rely on their troop to survive, so it’s important to form these relationships to successfully rehabilitate.
Female vervets stay in their troops for life and inherit rank from their mothers. However, the males must leave once they reach sexual maturity to be accepted into another troop. Thus, the males joining must be seen as dominant and gain respect from the high-ranking females and males in the new troop. If the male is not respected or viewed as dominant, he is chased away and left unable to survive without a troop (San Diego Zoo 2023). Those who do not inherit status within the troop use grooming and attention from higher-ranking members to create alliances (Bahr, New England Primate Conservancy 2021).
The author performing one of the observational sessions outside of Goldie’s Angels troop.
In the wild, vervets bond with one another and learn survival skills through play. They interact with individuals other than their mother within the first week of being born (Isbell & Jaffe 2013). By as early as three months they form playgroups with others their age (Bahr, New England Primate Conservancy 2021). During this pre-adolescent period, they spend the majority of their time in playgroups performing behaviors that will be used in adulthood, as well as practicing motor skills and establishing emotional attitudes that will be necessary later on (Lancaster 1971). They also begin mounting one another to establish hierarchies among themselves. Playful socialization is crucial in their development and sets the foundation for success in adulthood.
Biological troops have vervets of all age ranges, meaning that the infants can learn from and play with all the monkeys in the troop, unlike the surrogate troop at Bambelela, which has only infants and mothers. As of today, there are five rehabilitation troops at the site and two pre-rehabilitation troops. Rehabilitation troops were created at Bambelela from at least three or four different age groups (one year to five-plus years). These troops include young orphans, older orphans, older ex-pets, and injured but rehabilitated older monkeys. They are in the late stages of their rehabilitation process on the path toward release. The pre-rehabilitation troops, such as the Kindergarten, are in the early stages of forming and being conditioned away from human care. All the offspring in the rehabilitation troops were born to their biological mothers in the enclosure, while the Kindergarten is made up of only orphans and surrogate mothers. There is also the original Troop 9, which was released on the farm so that rehabilitators could continue watching their wild behaviors and apply them to rehabilitation practices. In addition, there are two Sanctuary troops that are unable to be released, including the Golden Oldies and the Handicap troop.
Those raised in the Kindergarten receive a lot of care and attention through their interactions with rehabilitators, which may lead to less competition and thus less push for dominant acts. By determining differences in behaviors, we could see what adjustments need to be made in the rehabilitation process that will result in more successful rehabilitation and releases. Such research may reveal areas in which the surrogate-raised infants are not developing fully or need more assistance with learning. It could pinpoint gaps in what the surrogate mothers and other orphans are able to teach and learn from one another. Confirming that the vervets being rehabilitated develop all the necessary behaviors for survival will determine if release will be successful (Guy et al. 2012).
Behavioral Observations of Biological and Surrogate-Raised Orphans
While conducting my research at Bambelela, I observed four troops in different stages of rehabilitation. The Kindergarten surrogate troop was made up of twenty-three orphans and four surrogate mothers. The three other troops (Abu’s Gang, Avengers, and Goldie’s Angels) were all adult troops whose infants were born in the enclosure to their biological parents. Abu’s Gang had thirty-three individuals, Avengers had thirty, and Goldie’s Angels had twenty-six. These troops received less frequent human interactions, only at feedings and for brief cleanings, and mimicked wild troops.
My day-to-day schedule was busy with a lot of hard work but extremely rewarding. The team of volunteers and permanent workers started with a morning meeting where we were assigned our projects for the day and given updates about the farm and the monkeys. After the meeting, we opened up our respective enclosures. I worked with the Handicap troop, which was made up of monkeys of all ages whose injuries made them unable to be released back into the wild or who were in recovery until they could be added to a pre-rehabilitation troop. Each morning, we scrubbed all the platforms, raked up old food, cleaned the bowls, added fresh water, and fed the infants. After completing my assigned project and assisting with the team project, I would return to the enclosure to feed the infants as well as Dolphina, an older low-ranking female who is unable to eat without assistance. After lunch, our team gathered in the food preparation area, filling the crates with food, making bowls, and chopping up all the produce, and then we returned to our respective enclosures to feed again. After we shut down the enclosures for the night, we had dinner together at the volunteer house, which had a kitchen and dining area with two alternating cooks.
Figure 1. Play Ethogram. All observed play behaviors listed and defined.
To conduct my research, I observed one troop for an hour, three times a day, and rotated which troop would be observed each day to ensure equal data was collected. The observations took place at 09:00, 12:00, and 16:00. I used all-occurrence sampling along with an ethogram to record any playful or dominant interactions observed during each session (Figures 1 and 2). An ethogram is a database of behaviors being observed with specific definitions. All-occurrence sampling occurs when, during observational sessions, all the ethogram behaviors are recorded every time they occur (Altmann & Altmann 1977). I also recorded each session on a Panasonic LUMIX FZ300 camera with an attachable microphone and reviewed each session to ensure no behaviors were missed.
I began each session by recording the date, troop name, and start time in my field notebook. I also recorded if a feeding occurred. Feedings were scattered frequently throughout the day and occasionally included vitamins or natural feedings such as reeds and plants. I then recorded each time a self-handicapping behavior occurred and what behavior it was, as well as each time a dominant or play behavior occurred and what behavior it was.
Self-handicapping occurs when an individual purposely puts themselves in a vulnerable position or at a disadvantage (Petrů et al. 2009). There are seven categories of self-handicapping defined in the ethogram that I recorded, including effort restriction (e.g., obviously and purposely not using all their strength when interacting with another), superior partner, disadvantaged position, physically demanding movements or postures, demanding substrates (e.g., wrestling while on a thin tree branch), carrying something in their hands, feet, or mouth, and restricted senses (e.g., having their eyes closed) (Petrů et al. 2009).
As for the play interactions, I recorded play faces, wrestling, chasing, play vocalizations, tug-of-war, hide-and-seek, and restricted or attempted bites (Pellis et al. 2014; Petrů et al. 2009; Struhsaker 1967a). Additionally, I noted whenever these behaviors occurred in a playgroup of three or more vervets. I also included self-play, jumping, tackle, and tag in my ethogram, because I noticed these behaviors were common during my first observational session.
Figure 2. Dominant Ethogram. All observed dominant behaviors listed and defined.
The dominant behaviors that I researched were territorial vocalizations, competition over resources, and threat faces (Bahr, New England Primate Conservancy 2021; Desboilles 2007) (San Diego Zoo 2023). I also looked at two displays, the penile display and the red, white, and blue display. A red, white, and blue display involves a vervet raising its tail to show another individual its genitalia, including a red anus, white medial strip, and blue scrotum (Struhsaker 1967b). A penile display is when a male vervet walks up to another, standing bipedally, directing its groin at the other male’s face, and placing its hands on the other’s shoulders, back, or head (Struhsaker 1967b). In both scenarios, the male doing the act is typically viewed as the more dominant member, while the one being acted on is of lower ranking. What I came to notice, however, was that these behaviors were very rarely seen performed by young vervets and were much more common among the adult males. The infants would, however, mount each other often to help establish their ranks within the troop early on.
The independent variables for this study were the two groups being studied: biological vs. surrogate raised. The dependent variable of this study was the frequency of play and dominant interactions observed within the two groups. After doing my observations and watching my footage each night, I input all my findings into an Excel spreadsheet. I organized this by troop name and then each behavior from the ethogram with their count totals as well as total play, dominant, and self-handicapping behaviors per session. Once all my data had been collected, I calculated the total number of play behaviors, self-handicapping, and dominant behaviors seen per troop for the entire span of my research. I then found the average amount for each category per observational session and calculated the average per monkey per troop to compare. An independent t-test was run to evaluate my data.
Initial Findings and What They May Suggest for Release
While running my preliminary averages, the surrogate infants exhibited more dominant and playful behaviors than the biological ones, contrary to my hypothesis. After running my independent t-tests, I determined that the difference between both play behaviors and dominant behaviors was statistically significant (Figure 3).
Figure 3: The tables show the average number of play and dominant interactions exhibited by vervets raised via surrogate mothers and those raised by their biological mothers. The biological infants averaged around 2.5 dominant interactions per observational session, while the surrogate infants averaged around 8 interactions. The surrogates also averaged around 80 play interactions compared with the biologicals’ 37. The comparison between play interactions and dominant interactions are statistically significant (p<0.001).)
It was a bit shocking to learn that those raised by surrogate mothers were more playful and displayed dominance more frequently. However, this may be explained by the setup of the troops. The Kindergarten had twenty-three infants with four mothers; meanwhile, the biological troops had only five or six infants per enclosure, each with its own respective mother. This creates more opportunities for play within the Kindergarten, and the four mothers are unable to keep all the infants in check the same way the biological mothers can in the rehabilitation troops. I cannot say for certain what repercussions will come from the overplaying or oversocialization of the surrogate infants. This could result in them having even more fine-tuned motor skills and movements, or it could result in them being reckless once released.
The difference in troop structure may also explain the acts of dominance. The infants being raised by surrogate mothers have been threatened only by other infants, the mothers, or wild monkeys and baboons outside of the enclosures who would occasionally antagonize them or try to steal food through the fences. As a result, they haven’t experienced true threats like they would in the wild, or don’t have an understanding of the strength of other adult individuals. Meanwhile, those in biological troops face threats from adult males, older juveniles, mothers who are not their own, and other outside threats. This may have forced them to learn their place in the troop and respond more submissively so as not to upset higher-ranking individuals. Additionally, those in biological troops are born into their rank and know their place from the start, whereas those in a surrogate troop are constantly fighting to establish ranks among the other infants. It is possible that these individuals being more dominant may help them integrate more easily into new troops upon release, or it may instill an incorrect sense of strength and superiority, which could be dangerous in the wild.
There is still much more data to analyze, and new findings are forthcoming. I hope that further analysis of this research will show the areas where improvements need to be made to the surrogate model and inspire new methods of enrichment. These would ideally encourage playful and dominant behaviors in moderation and discourage behaviors that leave the young vervets vulnerable or decrease their likelihood of surviving upon release. Improvements in rehabilitation tactics for this species could potentially be carried over to other species and rehabilitations using surrogate mothers (Guy et al. 2012).
Preparation and Takeaways from My Experience
What prepared me the most for this research in South Africa was spending two weeks in Namibia the semester before my IROP, as part of Dr. Conroy’s Livestock and Wildlife in Namibia course. We spent the course researching and studying the wildlife, and all the different cultures, beliefs, people, and history of the country, particularly its relationship with South Africa. We traveled all over Namibia with tour guides who were filled with information about anything and everything, and camped out on all different types of land. In doing so, we were exposed to many different beliefs, especially those surrounding wildlife. This allowed me to get used to traveling to and from Africa without navigating it alone. It also exposed me to what it is really like living in Africa, the languages, how the people are, what to expect, and what I would need to bring with me. I felt safer going to South Africa alone, knowing that people I had met in nearby Namibia would help me if I ever needed it.
In South Africa, there are eleven different languages, but English is common, and I never ran into any issues communicating or getting around. I didn’t experience culture shock, but that being said, I did work on a small, enclosed farm with people of all different backgrounds, and the nearest town was incredibly small. During my stay I was in a private room next door to a volunteer from Florida. Bambelela also has volunteer dorm-style housing, “the Village,” which was a community of houses where the permanent workers lived, the main house where the head workers lived, and the Chalets where tourists and visitors could vacation.
Many of the workers and volunteers were locals around college age like me, which was really nice because we could go into town together or play games after dinner. There were also guests and volunteers from all over the world, so I was exposed to many cultures all at once. During my stay, we had guests from the Netherlands, France, the UK, all over Africa, and many other countries.
This was such an incredible and life-changing experience. Aside from the obvious joys that come with spending every day working with monkeys, I made many friends I keep in touch with, and I learned a lot not only about vervets but also about Africa as a whole. Running my own research project allowed me to gain hands-on fieldwork experience, meet mentors and professionals in my field, and complete my capstone project here at UNH. I have always wanted to work in wildlife rehabilitation, and this has brought me one step closer to that goal. I graduated in December 2024 but am continuing to work with my data and will present it at UNH’s Undergraduate Research Conference in April 2025.
This was such a life-changing and impactful experience. I am so grateful to Dr. Conroy, Silke von Eynern, and everyone at the Hamel Center for Undergraduate Research for making this possible, especially my donors, the Class of 1952 International Research Fund and the Margaret (Clarke ’68) Norman International Research Fund. I am also grateful for UNH’s Dr. Curren and Dr. Jarema for helping me along the way and everyone at the rehabilitation center who taught me so much.
References
Altmann, S. A., & Altmann, J. (1977). On the analysis of rates of behaviour. Animal Behaviour, 25, 364–372. https://doi.org/10.1016/0003-3472(77)90011-2
African Wildlife Foundation. See what AWF is doing to protect the vervet monkey. 2019 Jul. African Wildlife Foundation. https://www.awf.org/wildlife-conservation/vervet-monkey.
Andresen, E., Arroyo-Rodríguez, V., & Ramos-Robles, M. (2018). Primate seed dispersal: Old and new challenges. International Journal of Primatology, 39(3), 443–465. https://doi.org/10.1007/s10764-018-0024-z
Bahr, L. L. (2021, December). VERVET Chlorocebus pygerythrus. New England Primate Conservancy. https://neprimateconservancy.org/vervet/
Butynski, T., & De Jong, Y.A. (2022, February 27). IUCN Red List of Threatened Species: Chlorocebus pygerythrus. IUCN Red List of Threatened Species; https://www.iucnredlist.org/fr/species/136271/205998680
Desbiolles, C. (2007). Behavioral traits in vervet monkeys: a longitudinal study of four successive birth cohorts. Escholarship.mcgill.ca. https://escholarship.mcgill.ca/concern/theses/f4752m48c
Guy A. J., & Curnoe, D. (2013). Guidelines for the rehabilitation and release of vervet monkeys. Primate Conservation, 27(1), 55–63. https://doi.org/10.1896/052.027.0103
Guy, A. J., Stone, O. M. L., & Curnoe, D. (2012). Assessment of the release of rehabilitated vervet monkeys into the Ntendeka Wilderness Area, KwaZulu-Natal, South Africa: A case study. Primates, 53(2), 171–179. https://doi.org/10.1007/s10329-011-0292-0
Harlow, H. F., & Suomi, S. J. (1971). Social recovery by isolation-reared monkeys. Proceedings of the National Academy of Sciences, 68(7), 1534–1538. https://doi.org/10.1073/pnas.68.7.1534
Healy A., & Nijman V. (2014). Pets and pests: Vervet monkey intake at a specialist South African rehabilitation centre. Animal Welfare, 23(3), 353–360. https://doi.org/10.7120/09627286.23.3.353.
Isbell, L. A., & Jaffe , K. (2013). Chlorocebus pygerythrus Vervet Monkey. In T. Butynski, J. Kingdom, & J. Kalina (Eds.), The Mammals of Africa: Vol II Primates (pp. 277–283). Bloomsbury Publishing.
Lancaster, J. B. (1971). Play-mothering: The relations between juvenile females and young infants among free-ranging vervet monkeys (Cercopithecus aethiops). Folia Primatologica; International Journal of Primatology, 15(3), 163–182. https://pubmed.ncbi.nlm.nih.gov/5001014/
Pellis, S. M., Pellis, V. C., Barrett, L., & Peter Henzi, S. (2014). One good turn deserves another: Combat versus other functions of acrobatic maneuvers in the play fighting of vervet monkeys (Chlorocebus aethiops). Animal Behavior and Cognition, 2(2), 128. https://doi.org/10.12966/abc.05.04.2014
Petrů, M., Špinka, M., Charvátová, V., & Lhota, S. (2009). Revisiting play elements and self-handicapping in play: A comparative ethogram of five Old World monkey species. Journal of Comparative Psychology, 123(3), 250–263. https://doi.org/10.1037/a0016217
Pillay, K. R., Streicher, J. P., & Downs, C. T. (2024). Trends in vervet monkey admissions to a wildlife rehabilitation centre: A reflection of human-wildlife conflict in an urban-forest mosaic landscape. Mammalian Biology, 104(6), 707–723. https://doi.org/10.1007/s42991-024-00447-x
Ramkissoon, Y. (2005). An assessment of the problem of vervet monkeys in the former Westville Borough: management implications. Ukzn-Dspace.ukzn.ac.za. https://ukzn-dspace.ukzn.ac.za/handle/10413/2395
San Diego Zoo. Vervet Monkey | San Diego Zoo Animals & Plants. (2023). Animals.sandiegozoo.org. https://animals.sandiegozoo.org/animals/vervet-monkey#:~:text=Males%20reach%20maturity%20at%20ab
Struhsaker, T. T. (1967a). Behavior of vervet monkeys and other Cercopithecines. Science, 156(3779), 1197–1203. https://doi.org/10.1126/science.156.3779.1197
Struhsaker, T. T. (1967b). Social structure among vervet monkeys (Cercopithecus aethiops). Behaviour, 29(2/4), 83–121. https://www.jstor.org/stable/4533186
van Niekerk, C., & Pillay, N. (2023). Behavioral responses of vervet monkey Chlorocebus pygerythrus infants in a novel fostering program. Journal of Applied Animal Welfare Science, 27(2), 330–342. https://doi.org/10.1080/10888705.2023.2186786
von Eynern, Silke—Interesting Facts and Activities—operating since 2003 with 30 releases done and over 1100 monkeys rehabilitated and released back into the Wild [rehabilitation and release success rate of around 80%]. Bambelela Wildlife Conservation NPC & Vervet Monkey Rehabilitation Farm, Groot Nylsoog KR447 in 0480 Bela Bela, Limpopo Province, South Africa.
Author and Mentor Bios
Originally from Easton, Massachusetts, Morgan Breen graduated from the University of New Hampshire in December 2024 with a bachelor of science degree in zoology. She served as the president of the UNH chapter of Best Buddies, an organization that offers one-to-one friendship and leadership development programs for individuals with and without intellectual disabilities.
Andrew Conroy is a professor of Animal Science and Sustainable Agriculture and Food Systems at the University of New Hampshire. He has mentored numerous Inquiry authors as well as many other undergraduate researchers who received grants from the Hamel Center for Undergraduate Research.
Morgan’s foreign mentor was Silke von Eynern, founder and conservation director of Bambelela Wildlife Care and Vervet Monkey Rehabilitation Facility in South Africa.
Copyright 2025 © Morgan Breen
