Prof. Simone Pika
04/2026
On April 1st, a new research project, supported by the Sievert Foundation, Osnabrück, Germany started at Osnabrück University, which is led by SImone Pika and aims to investigate exactly this question. To do so, quantitative data on trust in social interactions — such as grooming — will be collected among the Rekambo chimpanzees.
Updated: Oct 1, 2021
There’s an old saying: Health is wealth! No doubt this holds true for each and every living species on the planet. With the recent classification of chimpanzees as endangered species, it goes without saying that healthcare plays a vital role in the survival of the species. So, in today's article let’s dive into the topic of Healthcare in Chimpanzees! We will ask some important questions such as: What are the reasons for the rise in their mortality rate? Did the global pandemic affect one of our closest living relatives as much as it did affect us? Do chimpanzees self-medicate in ways similar to humans? And finally what are the guidelines followed in our field site to protect the health of our special chimpanzees.
There are different causes for the increase in the mortality rate of chimpanzees, including natural causes of death, such as illness, intercommunity encounters, and intraspecific aggression which fluctuate at natural levels across time and field sites. Nevertheless, they are connected to habitat loss and poaching pressures which are intensified or more frequent due to knock-on effects mainly from a lack of space or resources. Overall, most chimpanzees still die due to natural onset illness. It is the most common cause of death, through all ages and sexes with respiratory illness causing the highest mortality (Williams and colleagues, 2008). It is important to note however that anthropogenic pressures can introduce novel strains of a virus or a new bacteria that chimpanzees cannot naturally combat. Another cause of death in infant chimps is when their mother dies. Then their chance of survival is also very low. (Williams and colleagues, 2008).
Intercommunity aggression has the greatest impact on male adults and both male and female infants (Mitani and colleagues, 2010). In these intercommunity aggressions, individuals eventually die usually due to sustained injuries. Furthermore, poaching is one of the most prominent threats for chimpanzees across Africa. While the presence of researchers reduces this threat, it can at the same time increase the risk of human-to-ape transmission of diseases (Köndgen and colleagues, 2008).
The ongoing pandemic has a major impact on humans, but how has it affected our closest living relatives? Can SARS-CoV-2 also be a threat for them? The answer is: Yes! Since there is close contact between humans and habituated apes there is a high potential for the transmission of diseases. Not only can this happen because of research groups, but also through tourism and poachers. This is a dilemma as "Great Ape Tourism" is an important source of income in some African countries. The reduction of this could limit the funding towards healthcare and support of chimpanzee lives. Furthermore, the presence of researchers has a strong positive effect in suppressing poachers (read our "Research means Protection" article to dive deeper into the topic). In Loango, we take extensive measures to protect and care for the health of chimpanzees.
Well! On the positive side, it’s not all bad news. It has been hypothesized that much of human’s traditional knowledge stems from our ancestors observing the medicative behaviors of non-human animals. Chimpanzees are just one example of a species that has been shown to self-medicate (Huffman and colleagues, 2001), they do so by making use of the natural resources in their habitats. This behavior is known as zoopharmacognosy (Daoudi, S., 2016). The two most notable types of this self-medicative behavior observed in the wild are leaf swallowing and bitter pith chewing. These behaviors were first observed at the field sites, Mahale and Gombe in Tanzania, and Kibale in Uganda (Huffman and colleagues, 2001). The first observation in 1983 that left the scientists puzzled was the swallowing of the Aspilia spp. leaves. It was intriguing to them because this leaf species lacked any nutritional value in their diet (Wrangham and colleagues, 1983). It was not until 1996, that this behavior was discovered to be associated with self-medication as a means to expel parasitic worms via their feces (Huffman and colleagues, 1996). The chimpanzees were swallowing the leaves to take advantage of their rough and bristly surface that hooked onto the worms as the leaves passed through their digestive system, in turn purging their intestines of certain parasites. Furthermore, the chewing of the bitter pith of Vernonia Amygdalina became known as a clear indication of poor health, as also evidenced by diarrhea, lethargy, weight loss. It was shown to combat nematode worm infection. From a study by Huffman and colleagues (2001), that recorded two cases in detail, recovery from such symptoms was evident 20–24 hours after the chimpanzees chewed the bitter pith. The plant species used for these medicative events vary in form (herb, vine, shrub, and tree), but the common property functionally linking all of these forms is their bristly, rough-surfaced leaves. An individual may swallow anywhere from one to 56 leaves in one bout.
Image Sources: João Medeiros & Forestowlet
Now, how do humans factor in? In our ever-changing world, humans and non-human animals are coming into contact ever more frequently. The majority of these interactions are negative and often result in losses to the non-human animal side. In regards to chimpanzees and the other African apes, these populations are becoming ever more threatened by encroachments from human development and the subsequent pressures this places on an environment. However, there are now a number of specific research and tourism guidelines that have been implemented to protect the health and safety of great-apes under these conditions. At the Ozouga study site, we actively enforce hygiene measures and follow the "IUCN Best Practice Guidelines for Great Ape Tourism" (2010) even though at present our community is not exposed to tourist visitors. These regulations apply to research sites globally that work with great apes and provide advice on how to ethically interact in these shared environments. The most important rule when it comes to interaction with non-human great apes is - distance! As a rule of thumb, our interference with their daily lives is always kept to the bare minimum. Further, there must always be a minimum distance of eight meters between the researchers and the chimpanzees (we have been practicing maintaining distance long before it was necessary for the current COVID-19 pandemic health and safety measures!). The second most important rule is the mandatory use of surgical face masks. Chimpanzee research and tourism projects have documented known human pathogens like human respiratory syncytial virus (HRSV), the human metapneumovirus (HMPV), and the human rhinovirus C, that can cause mortality in wild chimpanzees. The wearing of surgical face masks is feasible, inexpensive, and has been shown as an effective barrier to exhaled pathogens.
In addition to these enforced rules, another important aspect of working around chimpanzees is, following basic hygiene practices. In 2017, a ‘Hygiene Barrier’ was built at our research camp to serve as a transition point between the camp and our daily work in the forest. All our fieldwork clothes and equipment are stored in the hut, and everyone is required to change before entering the camp after a day of long work in the forest. Hand washing and the use of sanitizers is a common affair all throughout the day. Furthermore, there are strict rules about what can be left in the forest. For example, fecal matter cannot be left in the forest and must be transported hygienically back to the camp where it will be disposed of in a safe way. Additionally, all staff members and individuals who may potentially come into visual contact with chimpanzees must be healthy and have no symptoms of the disease such as a fever or a runny nose. If any member of the team becomes sick they quarantine themselves until no longer contagious and in serious cases leave the camp immediately.
In the past years, a long-term health monitoring system has been implemented for all of our habituated community members. On a daily basis, the health conditions of the individuals are recorded and monitored for any signs of illness such as sneezing, coughing, or excessive diarrhea. The healing process of wounds when individuals become physically injured is also carefully monitored. In cases where an individual is observed showing symptoms of illness we follow this individual closely to monitor the progression of these symptoms and collect extra samples including urine, fecal, and blood matter when possible. This system allows us to create a database for monitoring the general health of the Rekambo community.
So far we have discussed all that is done to take care and protect our Ozouga Chimpanzees to the best of our abilities. Is there something that you, the general public, can do? Of course! You can share our objective and support us on our journey, to raise public awareness about our endangered relatives. We also very much appreciate any financial support to continue our efforts in the protection and conservation of this endangered species. If you’d like to join our cause you can donate to the Ozouga fund.
That’s all for today, we hope you enjoyed it!
Yours sincerely,
The Ozouga-Blogging-Team
References:
Daoudi, S. (2016, June 2). How other primates self-medicate – and what they could teach us. The Conversation. https://theconversation.com/how-other-primates-self-medicate-and-what-they-could-teach-us-59869
Wrangham, R.W., Nishida, T. Aspilia spp. Leaves: A puzzle in the feeding behavior of wild chimpanzees. Primates 24, 276–282 (1983). https://doi.org/10.1007/BF02381090
Huffman, M.A., Caton, J.M. Self-induced Increase of Gut Motility and the Control of Parasitic Infections in Wild Chimpanzees. International Journal of Primatology 22, 329–346 (2001). https://doi.org/10.1023/A:1010734310002
HUFFMAN, M. A. (2001). Self-Medicative Behavior in the African Great Apes: An Evolutionary Perspective into the Origins of Human Traditional Medicine. BioScience, 51(8), 651. https://doi.org/10.1641/0006-3568(2001)051
Köndgen, Sophie et al. “Pandemic human viruses cause decline of endangered great apes.” Current biology : CB vol. 18,4 (2008): 260-4. doi:10.1016/j.cub.2008.01.012
Williams, J M et al. “Causes of death in the Kasekela chimpanzees of Gombe National Park, Tanzania.” American journal of primatology vol. 70,8 (2008): 766-77. doi:10.1002/ajp.20573
Mitani, J. C., Watts, D. P., & Amsler, S. J. (2010). Lethal intergroup aggression leads to territorial expansion in wild chimpanzees. Current Biology, 20(12), R507–R508. https://doi.org/10.1016/j.cub.2010.04.021
Best practice guidelines for great ape tourism | IUCN Library System. (2010). Best Practice Guidelines for Great Ape Tourism. https://portals.iucn.org/library/node/9636
Updated: Oct 2, 2021
We previously discussed what chimps get up to on a daily basis, in our Daily Lives of Chimps article. Today, we intend to do some myth-busting and discuss the feeding and food assimilation patterns of chimpanzees. We will also look into whether chimpanzees demonstrate prosocial behaviors like the sharing of food, tool use, and teaching.
For starters (pun intended), we would like to clarify a myth that we likely all have encountered at some point in our life. That is, chimpanzees and other apes love bananas! We will just remind you of the depictions in the Disney movie: “The Jungle Book”. But it’s not just there that we encounter this image. Mainstream media have portrayed chimpanzees as ‘banana lovers’ for decades. Nonetheless, there have more recently been efforts by zoos to remove bananas from the diets of their chimpanzees due to health concerns, such as high sugar levels and the associated risks that follow it. Those might be rotting teeth or even diabetes. Yet, the assumption that chimpanzees and other apes like bananas is not completely unfounded, they really do enjoy them. One probable reason for that belief might be a study from back in the 1930s with captive monkeys. There they found that when given the choice between multiple food types the preference for bananas ranked pretty high, just below grapes, which are the first place (Katz & Katz, 1936). This information has for some reason made its way in many feeding guides for captive chimpanzees. They do like bananas, there is no debate about that. However one must always distinguish between captive chimpanzees and chimpanzees in the wild! Bananas are a plant species domesticated by humans which means that in the wild the chances of coming across this tasty treat is relatively low to non-existent.
Chimpanzees are essentially frugivores (fruit comprises ~⅔ of their diet), however, they also feed on leaves, insects, and other food types such as honey and meat. In Loango they access honey mainly from underground bee nests by using tools specifically designed for this purpose (Estienne and colleagues, 2017). Meat consumption is achieved by mammal predation, though still under investigation it seems that there may be an aspect of seasonality to hunting activity in different chimpanzee populations. Some other factors that influence the diet of chimpanzees are the presence or absence of prey species, competing predators, or human interference (McGrew, 1983).
We humans generally love to share our meals, but what about chimpanzees? Do they like to eat with kin and friends?
Unlike us humans, sharing food outside of kinship or mating relationships is rare across the animal kingdom. Yet, chimpanzees and bonobos are two of the rare exceptions. Insights into these behaviors in the non-human great apes might help us better understand the evolution of human cooperation. So let's take a closer look!
Some studies have shown that chimpanzees are more likely to share food with their friends and that neither high dominance status nor harassment by beggars influence their decision (Samuni and colleagues, 2018) though there is some variation, the rate of sharing is quite high in general (Silk and colleagues, 2013). Research also suggests that chimpanzees selectively share meat with receptive females. Such transfers have been reported to enhance immediate mating opportunities at Gombe (Stanford, 1998) and future mating prospects, but not immediate ones, in the Taï Forest (Gomes & Boesch, 2011). Furthermore, males selectively transfer meat to males that have also transferred the meat to them and to their allies. This has been observed in the Taï Forest of Côte d’Ivoire and in Ngogo in the Kibale Forest of Uganda (Mitani & Watts 1999, 2001; Boesch & Boesch-Achermann 2000; Mitani 2006). After group hunts sharing is observed quite frequently (Silk and colleagues, 2013). Tolerated theft (Blurton Jones, 1984) or sharing under pressure (Wrangham 1975; Stevens & Stephens 2002; Stevens & Gilby 2004) has been observed at Gombe wherein males give up parts of their kills to avoid the costs of defending a food item against persistent beggars.
By now we have just covered the general mechanisms at play when it comes to food sharing. But what does it actually look like when sharing takes place? Chimpanzees use a lot of gestures when begging for meat, for example, they stretch out their hands, and they also use vocalizations to demonstrate their desires i.e. with grunts and whimpers. Excitement over food might also be displayed via embracing, touching, kissing and even sociosexual behavior. So far, we have covered the observable part of behavior. But let's now take a look at what's happening “inside” of chimpanzees in these contexts. Oxytocin or more commonly known as “the love hormone” studied in humans is also found in the chimps and can be used to shed some light on their prosocial behavior. Samuni and colleagues (2018) found high levels of oxytocin, when meat and other valued foods were shared or after hunting with others. This suggests that oxytocin is a key hormone involved in cooperation in general. On a side note, the effects are highest for meat and honey, so there seems to be something special about them. But that is a story for another day.
Sharing also takes place in the form of teaching skills and sharing tools. For most wild chimpanzees, tool use is an important part of life -- but learning these skills is no simple feat. The capacity for teaching and sharing tools is predominantly observed in mother-child relationships. Apart from that, tool donors experienced significant reductions in tool use and feeding, while tool recipients significantly increased their tool use and feeding after tool transfers. Since tool transfers are costly to the teacher, tool donors also showed sophisticated cognitive strategies that effectively buffered them against potential costs. Tool transfers, for example, have been documented during honey extraction from underground beehives by our chimpanzees in the Loango National Park. Given the complexity of these tool tasks, tool transfers from skilled chimpanzees to less competent conspecifics constitute a form of teaching.
In video: Rekambo chimps extracting honey from underground beehives
We would like to end this article with an interesting quote that not only covers teaching in chimpanzees but also its probable impact on the evolution, “Teach a chimpanzee to fish for insects to eat, and you feed her for a lifetime. Teach her a better way to use tools in gathering prey, and you may change the course of evolution.” (Musgrave, 2019)
Yours sincerely,
The Ozouga-Blogging-Team
References:
(1936), Some Problems concerning the Feeding Behaviour of Monkeys. By Professor DAVID KATZ, Ph.D., and ROSA KATZ, Ph.D.*. Proceedings of the Zoological Society of London, 106: 579-582. https://doi.org/10.1111/j.1469-7998.1936.tb08519.x
Samuni L., Preis A., Mielke A., Deschner T., Wittig R. M. and Crockford C. 2018. Social bonds facilitate cooperative resource sharing in wild chimpanzees. Proc. R. Soc. B. 285: 20181643 20181643 https://doi.org/10.1098/rspb.2018.1643
Estienne, Vittoria & Stephens, Colleen & Boesch, Christophe. (2017). Extraction of honey from underground bee nests by central African chimpanzees ( Pan troglodytes troglodytes ) in Loango National Park, Gabon: Techniques and individual differences. American Journal of Primatology. 79. 22672. 10.1002/ajp.22672.
Washington University in St. Louis. "Chimpanzees more likely to share tools, teach skills when task is complex: Study has implications for evolution of technology and culture in humans." ScienceDaily. ScienceDaily, 24 December 2019.
Silk, Joan & Brosnan, Sarah & Henrich, Joseph & Lambeth, Susan & Shapiro, Steven. (2013). Chimpanzees share food for many reasons: The role of kinship, reciprocity, social bonds and harassment on food transfers. Animal Behaviour. 85. 941–947. 10.1016/j.anbehav.2013.02.014.
Stephanie Musgrave, Elizabeth Lonsdorf, David Morgan, Madison Prestipino, Laura Bernstein-Kurtycz, Roger Mundry, Crickette Sanz. Teaching varies with task complexity in wild chimpanzees. Proceedings of the National Academy of Sciences, 2019; 201907476 DOI: 10.1073/pnas.1907476116
McGrew, W.C. Animal foods in the diets of wild chimpanzees (Pan troglodytes): Why cross-cultural variation?. J. Ethol. 1, 46–61 (1983). https://doi.org/10.1007/BF02347830
Stanford, CB. Chimpanzees and Red Colobus. Cambridge, Massachusetts: Harvard University Press; 1998.
Gomes CM, Boesch C. Wild chimpanzees exchange meat for sex on a long-term basis. PLoS One. 2011; 4:e5116. [PubMed: 19352509]
Mitani, JC. Reciprocal exchange in chimpanzees and other primates. In: Kappeler, PM.; van Schaik, CP., editors. Cooperation in Primates: Mechanisms and Evolution. Heidelberg: Springer-Verlag; 2006. p. 101-113.
Mitani JC, Watts DP. Demographic influences on the hunting behavior of chimpanzees. American Journal of Physical Anthropology. 1999; 109:439–454. [PubMed: 10423261].
Mitani JC, Watts DP. Why do chimpanzees hunt and share meat? Animal Behaviour. 2001; 61:915– 924.
Blurton Jones NG. A selfish origin for human food sharing: tolerated theft. Ethology and Sociobiology. 1984; 5:1–3.
Wrangham, RW. Ph.D. thesis. Cambridge University; 1975. Behavioural ecology of chimpanzees in Gombe National Park, Tanzania.
Stevens JR, Stephens DW. Food sharing: a model of manipulation by harassment. Behavioral Ecology. 2002; 13:393–400.
Stevens JR, Gilby IC. A conceptual framework for nonkin food sharing: timing and currency of benefits. Animal Behaviour. 2004; 67:603–614.
Boesch, C.; Boesch-Achermann, H. The Chimpanzees of the Taï Forest: Behavioural Ecology and Evolution. Oxford: Oxford University Press; 2000.
