White-eyelid mangabeys

Finally inku!

I just came back from a four-day trip to the south. Last Thursday I left camp accompanied by two men from the village: Edito, a serious-looking experienced hunter who regularly joins the anti-poaching patrols that cover the area south of LuiKotale, and Michokoto, a younger and slightly less timid man. My aims were clear: visiting several forest clearings, searching for animals, specifically monkeys, and most importantly, finding golden-bellied mangabeys (Cercocebus chrysogaster). I brought some tubes, as I had also planned to try to get fecal samples of monkeys. These samples could be useful for a possible future project. So the next four days I would spend my time with Edito and Michokoto, who would be my guides, porters, cooks, research assistants and body guards. Both were carrying two tents and our provisions consisting of several kilos of kwanga (the manioc paste that forms the staple of the local diet), a whisky bottle filled with palm oil, three coconuts and some smoked fish. I asked my companions if they would like to carry a mundele backpack. A stupid question. Of course they preferred their jaguar: a rack made of nicely woven wooden sticks, open at the front, but everything packed in a jaguar is hold together with pieces of liana. A jaguar has two liana straps at the shoulder and an optional strap that goes around the forehead. Some old pieces of clothing make carrying a jaguar a bit more comfortable. Both my guides were wearing simple flip flops, taking them off as soon as we hit a muddy spot. The Congolese way of going on a four-day hike seems rough to us, but tough as they are, these guys just go for it.
After crossing Libeke ya Badzungu (libeke means clearing) at the southern edge of the study site, we left the frequently walked trails. From now on I had to rely on Edito for navigation. These trails are only walked by the occasional patrols that come through, by poachers and elephants. Mainly the latter I hoped. However, most trails are barely visible to the inexperienced eye. Edito relied on some cut marks here, a broken branch there and now and then an inscription in the bark of a tree, the local graffiti. I was really amazed by Edito’s navigation skills in the forest. We went more than twenty kilometers south of LuiKotale in an area where he hadn’t been since the last patrol in April, but he perfectly managed to find his way without a compass or gps. Often the trail was confusing as a tree had fallen on the path and several deviations had been formed by previous passengers. I saw possible trails in every direction, but Edito and Michokoto spread out on both sides and as one of them whistled, we knew where to go again. To make it less confusing in the future, Edito would then cut and break a sapling or make some small cut marks in the bark of a tree. We often stopped on a specific spot, to listen for monkeys or poachers, and then Edito would recall that this or that had happened on a previous patrol on this specific spot. Each time I was totally amazed by his memory. Behind one tree they saw a nkulupa duiker together with Abana, on another spot they encountered bonobos.

After three hours of walking we reached a small savannah patch: Momentaole. While walking through the waist-high grass, we heard bonobos south. Ten minutes later we were standing below a bodzilo mpongo tree (Parinari excelsa) observing bonobos. I took my camera and filmed these truly wild bonobos before they noticed me. In contrast to my expectation, they didn’t instantaneously flee upon detection. The bonobos were not pleased with our presence and made that clear by barking at us. A couple of them moved to a nearby tree, but they didn’t flee. Could I be observing virtually naive bonobos? Great apes that live in extremely remote areas often do not flee when contacted by humans and sometimes even approach their observers. That is exactly what happened. I noticed a subadult female who was not barking at all. She seemed more relaxed and climbed the trees above us to have a better look at these weird-looking bipedal primates on the forest floor. Although these bonobos have definitely seen humans before, they must have never had negative experiences with humans. Or this subadult female could possibly have been an ex-LuiKotale female who joined this group to the south. When we left half an hour later this female was still hanging around in the trees ten meters above the trail.
Two hours later we hit a very wide, well-maintained trail. This was not a human-maintained trail, however. This was a clear path walked by generations of forest elephants (Loxodonta cyclotis). Highways that connect important locations in the life of elephants. The trail became gradually more swampy and led us to Libeke ya Loombo, a nice clearing filled with butterflies and swallows sweeping along the surface of a slow-flowing stream. Edito and Michokoto were excited to see so many fish swimming along our feet. We saw more traces of elephants and bongos (large forest antelopes, Tragelaphus euryceros) at the other end of the clearing and found our camping spot for the night three hundred meters further. Being the youngest of the two, Michokoto was responsible for clearing the spot with a machete, setting up the tents and preparing food. Edito made the fire going with bougies locales, the highly flammable resin of a tree we found on the way. Michokoto cut some saplings and quickly made me a bench with a small table where he later presented me roasted peanuts as an afternoon snack. Edito and I spent the last hours before sunset looking for monkeys, while Michokoto prepared the meal of kwanga and smoked fish. We ate together next to the fire. I tried to catch sleep on the uneven floor quite early to be ready to search for more monkeys (and their feces) the next morning. The following days went just like that, as we went from one clearing to the other with names like Kaotsikitende, Ntoka and Nzelo.
The second night we camped close to a three-hundred meter wide forest clearing, called Ntoka, where it was planned Edito would go night-fishing to replenish our supplies. By that time we had had several conversations in Lingala and I felt like I got to know my new Congolese friends pretty well. In my enthusiasm I suggested joining Edito to learn more about this way of fishing. A decision I will maybe not take next time. Edito was surprised, but encouraged my enthusiasm and happily accepted my offer. The moon was still up, so we had to wait a bit. The western technology of my gps told me moon set would be at 21h51. It was after dinner at seven that we agreed to leave at nine o’clock. In the meantime I was slightly regretting my suggestion, as I was already struggling to stay awake. But I could not crawl back anymore, so I went to my tent to catch some sleep and at nine I was ready to go. By that time Edito and Michokoto were already asleep next to the fire, so we only left at nine thirty. Navigating through the dark was a challenge, but Edito knows the forest, so after doing a loop that fooled any sense of orientation in me, we arrived at the forest edge. I followed Edito as he walked through the shallow waters of the clearing spotting sleeping fish with his torch. A quick stroke of his machete and that’s the first one. Fish after fish disappeared in our cooking pot. The sounds of frogs and the mist above the water gave this night a kind of calmness I have rarely sensed. At one point a sitatunga (Tragelaphus spekei) was calmly standing fifteen meters in front of us. After half an hour I felt the fatigue sweeping in, but Edito kept going for every fish. It was only after an hour and a half that we slowly started to head back to camp. Slowly, because only now I remembered that Edito had said we would come back via the river that flows into the clearing. Crawling through vines in knee-deep waterlogged mud in the middle of the night is not what I had in mind when I suggested to go night-fishing. Edito was looking under tree roots to get every fish. During the day he had asked me if he could kill a dwarf crocodile (Osteolaemus tetraspis) if we would come across this njama mabe, bad animal. I explained him we would leave the animal in peace and killing it was not necessary. But when we did come across a lokese that night, I was too confused and too tired to realize what was going on. Edito whispered nakoboma ye and before I could intervene, he killed the 50-cm crocodile with a single hit of his machete. Where the river became clearer further upstream, Edito put a couple of branches on the river bank, threw the fish on them and started cleaning every single fish. It was one o’clock at night when we reached our camp site. I was exhausted. I closed my eyes and fell asleep immediately. During the rest of the night Edito and Michokoto further processed and smoked the fish and crocodile on a small rack of sticks above the fire. The animal was killed instantaneously, so no welfare issues involved, and the ecological impact of this hunt was probably minimal. Hence, our next lunch consisted of kwanga and smoked dwarf crocodile. Not really my favorite.
During one of our hunts for monkey feces, Edito and I were crawling upon a polyspecific group consisting of black mangabeys (Lophocebus aterrimus), yellow-nosed redtailed guenons (Cercopithecus ascanius whitesidei) and Wolf’s guenons (Cercopithecus wolfi). Both of us didn’t have much experience with this work. When some of the monkeys had detected us, Edito wanted to try a different technique. Nakobanga yango. He would frighten them. He heavily shook two saplings for over thirty seconds and imitated the call of a crowned eagle (Stephanoaetus coronatus). When an eagle catches a monkey, both of them often fall to the ground and a severe wrestle follows. This simulated eagle attack provoked an intense response from all animals in the group. A loud concert of different species-specific alarm calls lasted for about twenty minutes. Some monkeys came closer to keep an eye on the eagle that was not there. When the monkeys finally calmed down and left the scene, we searched the area and found a single fecal sample. This old hunting technique was maybe not the best strategy for our scientific purpose.
We collected more samples than I expected, but by the last evening we still hadn’t heard any sign of golden-bellied mangabeys. I was already thinking to plan a second trip to the south, focusing only on searching golden-bellied mangabeys. The morning of the fourth day we left camp at sun rise to try one more time. After five hundred meters we heard movement in the trees, but the calls told us this was a group of redtails. I am really happy that I learned all the calls of the monkeys in these forests. Most of the time I know the species before I see a monkey, just based on the calls they make. Half an hour later we heard more branch movement a couple of hundred meters to the south and Edito said: inku! I was not expecting golden-bellied mangabeys and I hadn’t heard a single call, so I didn’t put a lot of faith in Edito’s species identification. But as we were heading south, I heard monkey calls in the distance that I only recognized from my work at Bai Hokou in the Central African Republic. This was a group of inku, the golden-bellied mangabey! Then it all went quick. We heard more calls from further away. Edito said rapide and rushed through the forest to catch up with them. Exactly at seven o’clock I saw my first wild golden-bellied mangabey, finally inku! The group was about thirty meters in front of us moving through the canopy. I saw several adult males with their massive posture and nice golden fur on the belly. I saw females carrying infants and juveniles jumping from one tree top to the next. I took my camera and sound recorder and tried to capture the moment as best as possible. Golden-bellied mangabeys belong to the semi-terrestrial white-eyelid mangabeys (genus Cercocebus). After following the group for half an hour the first individuals started coming to the ground. It was impossible to make an accurate estimate of the size of the group, but white-eyelid mangabeys are known to form huge groups of more than a hundred individuals in certain forests. Golden-bellied mangabeys only occur south of the Congo River in the Democratic Republic of Congo and no one has studied them in the wild. Probably very few western people have seen them in their natural habitat. The World Conservation Union (IUCN) does not have enough data to evaluate its conservation status. A special monkey and I am very pleased that I got to follow a group for 1h20. Even better is that I got a total of ten fecal samples. Mission accomplished.The walk back to LuiKotale was longer than I thought and I was physically quite tired from the walking and lack of good sleep. But my mental batteries were fully charged. All my aims and expectations for this trip were fulfilled. We did see monkeys and other animals like sitatungas and red river hogs (Potamochoerus pictus). We crossed some wonderful forest clearings and we were able to avoid elephants and poachers (although we did see signs of both). We did get plenty of fecal samples, and I saw golden-bellied mangabeys! As I was going through this list of achievements on the way back, my Congolese companions were as proud as ever and thanked God for the help. I’m not an anthropologist, but for four days I liked pretending to be one.

Opportunistic behaviour of white-eyelid mangabeys

White-eyelid mangabeys share a common foraging strategy with mandrills and drills (genus Mandrillus) characterized by rummaging through the leaf litter in search of fallen fruits and invertebrates. Both genera are generalized omnivores noted for their adaptability and opportunistic behaviour. The following three examples highlight the explorative, opportunistic behaviour of white-eyelid mangabeys.

Agile mangabeys (Cercocebus agilis) have been studied at the Mondika and Bai Hokou field sites in Dzanga-Ndoki National Park, Central African Republic, where forest elephants (Loxodonta cyclotis) are present. At both sites, mangabeys have been regularly observed sifting through elephant dung piles to pick out the edible seeds. This seed predation may have an important impact on forest dynamics by counteracting the seed dispersal services provided by forest elephants. Sifting through elephant dung has also been observed when a group of approximately 200 agile mangabeys visited Dzanga Bai, a large forest clearing in the same national park. It is not known how widespread this behaviour is. It would be interesting to know if it also occurs at other sites where mangabeys share their habitat with elephants.

An adult male agile mangabey (Cercocebus agilis) sifting through an elephant dung pile at Bai Hokou.

After the dry season of 2010, large mushrooms of the family Russulales began to appear in mono-dominant forest patches of cursief: Gilbertiodendron trees at Bai Hokou. The agile mangabeys spend on average 5% of their time in this forest type. However, during the two weeks when these mushrooms were highly available, they spent approximately 17% of their time in this forest, specifically to exploit this temporary resource. This permanent large group of 135 individuals, during the study period, could be seen foraging through this open type of forest checking for fresh mushrooms under each leaf on the forest floor. The group spent almost 40% of their foraging time consuming mushrooms. The same opportunistic behaviour has also been observed at Mondika.

Agile mangabeys (Cercocebus agilis) feeding on a mushroom at Bai HokouJuvenile agile mangabey (Cercocebus agilis) feeding on a mushroom at Bai Hokou.

Agile mangabeys (Cercocebus agilis) feeding on mushrooms at Bai Hokou.

Some frog species produce terrestrial foam nests to escape predation by aquatic creatures. They lay their eggs in a gelatinous mass attached to leaves, branches or tree trunks above a surface of water. When the tadpoles have developed to a certain stage, they are washed off by heavy rain. Sooty mangabeys (Cercocebus atys) at Taï in Ivory Coast, are known to feed on the foam nests of two species of frog (Chiromantis rufescens, Hyperolius sp.). Once detected, the mangabeys would scoop out the eggs with their fingers, suck them from the leaf, or swallow the whole leaf. Nests may contain 100 to 200 eggs with a diameter of 2 to 3mm. Frog eggs probably represent a valuable, although opportunistic, protein source and observations suggest that the mangabeys deliberately searched for this food source. They would even jump into the water to harvest foam nests out of reach. Foam nest raiding is also known from samango monkeys (Cercopithecus mitis stuhmanni) in Southern Africa. Similar behaviour is also likely to occur in agile mangabeys (Cercocebus agilis) at Bai Hokou. On two occasions, individuals were seen eating a kind of foam attached to tree roots above water pools created by elephants, although the foam did not appear to contain eggs when checked by the observer. The mangabeys did not show the deliberate searching behaviour observed at Taï, but did spread out the remaining foam on a surface, like mangabeys do at Taï. If anyone could confirm whether this could be a foam nest of a frog species, please leave a reply.

A juvenile agile mangabey (Cercocebus agilis) eating foam at Bai HokouA juvenile agile mangabey (Cercocebus agilis) eating foam at Bai Hokou.

A juvenile agile mangabey (Cercocebus agilis) spreading out the foam at Bai HokouThe result of an agile mangabey (Cercocebus agilis) spreading out the foam.

A juvenile agile mangabey (Cercocebus agilis) eating foam at Bai Hokou.

Key references:
Devreese L. (2011). Many hands make light work. Foraging strategy of agile mangabeys (Cercocebus agilis) exhibiting a permanent large grouping pattern at Bai Hokou, Central African Republic. Master thesis, University of Antwerp, Belgium.

Rödel M-A., Range F., Seppänen J-T. & Noë R. (2002). Caviar in the rain forest: monkeys as frog-spawn predators in Taï National Park, Ivory Coast. J. Trop. Ecol. 18: 289-294.

Shah N. (2003). Foraging strategies in two sympatric mangabey species (Cercocebus agilis and Lophocebus albigena). Ph.D. Thesis, State University of New York, Stony Brook.

Written by Lieven Devreese on December 15, 2013.

Durophagy among white-eyelid mangabeys

White-eyelid mangabeys are known for their durophagous diet, which means they rely a lot on very hard foods. Their teeth are adapted for this type of diet and they have, for example, some of the thickest dental enamel of all extant primates, as well as enlarged incisors and special formed premolars molars. Sooty mangabeys (Cercocebus atys) at Taï in Ivory Coast are known to eat a lot of seeds of a tree called Sacoglottis gabonensis. Often the group can be heard from a distance when cracking open these hard seeds. The mangabeys crush the seeds with their postcanine teeth, while chimpanzees use tools to access them. Red-capped mangabeys (Cercocebus torquatus) at Sette Cama in Gabon also rely on Sacoglottis seeds, but their diet includes a more unusual food too. Red-capped mangabeys at this site use their canine teeth to open the shell of crabs (Cardisoma armatum) which they find near the coast. The video below illustrates durophagy among agile mangabeys (Cercocebus agilis) at Bai Hokou in the Central African Republic. In February-March 2010 this group frequently visited a patch in the forest where a lot of Strychnos trees bore large fruits with a hard outer layer. Using their incisor teeth, the mangabeys gnaw through this tough layer to get to the nutritious pulp inside. This group of, at that time, 135 individuals was normally constantly moving, but could stay for several hours at this patch. It is a special moment when more than one hundred mangabeys are gnawing around you!


This photo shows the skull of an agile mangabey (Cercocebus agilis) at the Royal Museum for Central Africa in Tervuren, Belgium. Note the enlarged incisor teeth. White-eyelid mangabeys use different teeth to manipulate different hard-object foods.

Written by Lieven Devreese on November 21, 2013.

Key references:
Cooke C. (2012). The feeding, ranging, and positional behaviors of Cercocebus torquatus, the red-capped mangabey, in Sette Cama Gabon: a phylogenetic perspective. Ph.D. Thesis, Ohio State University.

Daegling D.J., McGraw W.S., Ungar P.S., Pampush J.D. & Vick A.E. (2011). Hard-object feeding in sooty mangabeys (Cercocebus atys) and interpretation of early hominin feeding ecology. PLoS ONE 6: e23095.

Devreese L. (2011). Many hands make light work. Foraging strategy of agile mangabeys (Cercocebus agilis) exhibiting a permanent large grouping pattern at Bai Hokou, Central African Republic. Master thesis, University of Antwerp, Belgium.

Devreese L., Huynen M.C., Stevens J.M.G. & Todd A. (2013). Group size of a permanent large group of agile mangabeys (Cercocebus agilis) at Bai Hokou, Central African Republic. Folia Primatol 84: 67-73.

McGraw W.S., Vick A.E. & Daegling D.J. (2011). Sex and age differences in the diet and ingestive behaviors of sooty mangabeys (Cercocebus atys) in the Taï Forest, Ivory Coast. Am J Phys Anthropol 144: 140-153.

McGraw W.S., Pampush J.D. & Daegling D.J. (2012). Brief Communication: Enamel thickness

in mangabeys revisited. Am J Phys Anthropol 147: 326-333.

Shah N. (2003). Foraging strategies in two sympatric mangabey species (Cercocebus agilis and Lophocebus albigena). Ph.D. Thesis, State University of New York, Stony Brook.

Cercocebus.be online!

Welcome to the first website completely dedicated to the genus Cercocebus. Although white-eyelid mangabeys are known to science since the end of the 18th century (Kerr, 1792), they remain poorly understood because of the challenges associated with studying them in the wild. Cercocebus.be aims to bring information on the taxonomy, distribution, ecology and behaviour of these mysterious primates to you, scientist, naturalist or enthusiast.


This website is dedicated to the genus Cercocebus. Although white-eyelid mangabeys are known to science since the end of the 18th century (Kerr, 1792), they remain poorly understood because of the challenges associated with studying them in the wild. Cercocebus.be aims to bring information on the taxonomy, distribution, ecology and behaviour of these mysterious primates to you, scientist, naturalist or enthusiast.