Moukalaba-Doudou National Park Research Articles

Death of a one-armed blackback male due to severe injuries in a group of wild western lowland gorillas (Gorilla gorilla gorilla) in Moukalaba-Doudou National Park, Gabon.

The survival of limb-disabled primates in the wild has been widely reported. Nevertheless, their ultimate fate is little documented. It is important to understand the influence of limb disability on primate survival from a conservation perspective, as many African great apes suffer from limb injuries caused by entrapment in snares. Here, we report the death of a one-armed blackback male in a large one-male group of wild western lowland gorillas. The subject was a blackback male (14 years old) named Dodo, who lost his right forearm in August 2008. On 8 December 2019, Dodo was found to have suffered serious bleeding injuries to the front of his body, including large lacerations and puncture wounds. On 14 December his corpse was found in the forest. We provide evidence to suggest that his injuries were more likely caused by intraspecific aggression, though a predatory attack by a leopard could not be completely ruled out. His one-armed disability could have made him more vulnerable to attack from either a gorilla or leopard and led to his fatal injury. This report shows that a gorilla who had previously overcome a disability in one arm in childhood may die prematurely, in part, owing to this disability in young adulthood.

Diversity of gastrointestinal parasites in sympatric mammals in Moukalaba-Doudou National Park, Gabon.

Background and Aim:Gastrointestinal parasites identified in the wild can negatively affect host fitness, lower performance, and growth. On the other side, sympatric mammals that share habitat and resources may also cross-transmit parasites, which are often zoonotic and can contribute to morbidity and mortality. This study aimed to characterize the diversity of gastrointestinal parasites circulating in mammalian hosts in Moukalaba-Doudou National Park.Materials and Methods:We screened a total of 25 fecal samples collected from nine wild mammalian species, namely, western gorilla (Gorilla gorilla gorilla), chimpanzee (Pan troglodytes), putty-nosed monkey (Cercopithecus nictitans), African forest elephant (Loxodonta cyclotis), African buffalo (Syncerus caffer), blue duiker (Philantomba monticola), bay duiker (Cephalophus dorsalis), and red river hog (Potamochoerus porcus) as well as people working as trackers (Homo sapiens) using direct microscopic observations following a sedimentation technique to concentrate the fecal material.Results:Of the total 25 fecal samples screened, 15 (60%) were positive for parasitic gastrointestinal infection. Based on the morphology of parasite eggs and cysts, we identified a rich diversity of nematodes, protozoans, trematodes, and cestodes, including unidentified strongyles (73%), Oesophagostomum spp. (53%), Ancylostoma spp. (27%), Trichuris spp. (13%), Ascaris spp. (13%), Mammomonogamus spp. (13%), Strongyloides spp. (47%), Balantidium coli (20%), Entamoeba coli (20%), Endolimax nana (6%), Fasciola hepatica (6%), Paramphistomum spp. (13%), and Taenia spp. (6%).Conclusion:All parasites were found at least once in one of the hosts, and most were potentially zoonotic and responsible for several diseases of public health concern. Because of the small sample size, our findings should not be considered conclusive. Nevertheless, they highlight the diversity of gastrointestinal parasites in this area.

Seasonality in daily movement patterns of mandrills revealed by combining direct tracking and camera traps.

Movement is a fundamental characteristic of animals, but challenging to measure noninvasively. Noninvasive methods for measuring travel have different weaknesses, so multiple techniques need to be applied multiple techniques for reliable inferences. We used two methods, direct tracking and camera trapping, to examine the variation in time and seasonal differences in movement rates of mandrills (Mandrillus sphinx), an elusive primate that lives in large groups in central Africa. In a 400-km2 rainforest area in Moukalaba-Doudou National Park, Gabon, we tracked unidentified groups 46 times from 2009 to 2013. We systematically placed 157 terrestrial camera traps in the same area from 2012 to 2014 and recorded groups 309 times. Generalized additive mixed models (GAMMs) of the tracking data indicated that the group travel speed varied with time and season. In the fruiting season, the movement rate fluctuated with time in a bimodal pattern, whereas in the nonfruiting season, it increased monotonously with time. The predicted day range was longer in the fruiting season (6.98 km) than in the nonfruiting season (6.06 km). These seasonal differences suggest responses to changes in food resources and temperature. Camera-trap detection rates showed similar temporal and seasonal patterns to the tracking data, allowing us to generalize our findings to the population level. Moreover, cameras never detected mandrills at night, and we observed that they slept high in trees and hardly moved until the next morning, all suggesting their strict avoidance of nighttime movement. This study demonstrated the significance of the multiple-method approach in drawing robust conclusions on temporal patterns of animal movement.

Gorilla Abundance Estimations within North-East Moukalaba-Doudou National Park, Gabon

Accurate measures of animal population densities are essential to evaluate conservation status and implement action plans to ensure species survival. Gorilla numbers were assessed using the recce survey method within Moukalaba-Doudou National Park (MDNP) in Gabon using fresh nest counts of up to 1 week old. We walked 3,592 km within a 23.01-km² study site totalling a sampling effort of 297 days. Encounter rate was 0.12 fresh nests per kilometre, and gorilla density estimates generated by home range sizes (by minimal convex polygon) ranged between 1.14 and 1.48 gorillas/km². Gorillas preferred mixed forest for nesting over other habitats (Cheason index value 1.31). Results showed that gorilla density values within the study area concurred with previous studies that used line transect methodologies. We conclude that the choice of sampling design is dependent on environmental conditions characterised by each habitat type and target species.

Hand preference in unimanual and bimanual coordinated tasks in wild western lowland gorillas (Gorilla gorilla gorilla) feeding on African ginger (Zingiberaceae).

Bimanual coordinated behaviors are critical for detecting robust individual hand preference in nonhuman primates but are particularly challenging to observe in the wild. This study focuses on spontaneous feeding behavior on African ginger (Aframomum sp. and Renealmia sp.), which involves a unimanual task (reaching and pulling out a ginger stem) and a bimanual coordinated task (extracting pith from a ginger stem) by wild western lowland gorillas. Study subjects were 21 gorillas in the Moukalaba-Doudou National Park, Gabon. We examined whether they exhibit significant hand preference at the individual and group levels for both tasks. Sixteen gorillas showed significant hand preference in the unimanual task, whereas all 21 individuals showed significant hand preference in the bimanual coordinated task. Hand preference was significantly stronger in the bimanual coordinated task than in the unimanual task. It is noteworthy that gorillas showed a significant right-hand preference at the group level for the bimanual task (roughly 70% of the subjects). This study confirmed that bimanual coordinated tasks are more sensitive in detecting hand preferences in nonhuman primates. In addition to the bimanual nature of the task, the precision grip for processing and the importance of African ginger as a food resource might influence the expression of hand preference. Evidence of a group-level right-hand preference may support the "postural origins theory." Because all wild African great apes feed on the pith of African ginger, comparing this task and its hand preferences can contribute toward a better understanding of the evolution of handedness in Hominidae.

Human-Elephant Conflict Around Moukalaba-Doudou National Park in Gabon: Socioeconomic Changes and Effects of Conservation Projects on Local Tolerance

Human-elephant conflict (HEC) poses a serious problem in Africa for both local livelihoods and elephant conservation. Elephant damage is the price local people pay for coexisting with this species, and is assumed to reduce tolerance for elephants. However, conservation-related projects, through the benefits they offer may enhance local tolerance toward elephants. This study aimed to examine how crop damage by elephants and the benefits gained from conservation activities affect local people’s tolerance toward elephants around Moukalaba-Doudou National Park in southwest Gabon based on long-term ethnographic research and interview surveys in two periods (2010 and 2019). Based on the results, crop damage by elephants had a significant negative impact on the local social economy, leading to a decrease in human population in the area and making local people highly resentful of elephants. However, in one of the villages where employment from research and conservation activities was concentrated, many acknowledged the benefits associated with wildlife and expressed high tolerance for elephants. These findings suggest that benefits from conservation activities can increase tolerance toward elephants, which is negatively affected by the crop damage they cause. However, it should also be noted that externally generated projects have limitations and drawbacks. It is important to establish a system in which the benefits of conservation are shared widely and distributed appropriately, and wherein income resources are diversified. Multisectoral interventions focusing on local socio-ecological vulnerability are needed to mitigate human-elephant conflict and advance the conservation of African elephants.

Genomic Analyses of Bifidobacterium moukalabense Reveal Adaptations to Frugivore/Folivore Feeding Behavior.

Despite the essential role of Bifidobacterium in health-promoting gut bacteria in humans, little is known about their functions in wild animals, especially non-human primates. It is difficult to determine in vivo the function of Bifidobacterium in wild animals due to the limited accessibility of studying target animals in natural conditions. However, the genomic characteristics of Bifidobacterium obtained from the feces of wild animals can provide insight into their functionality in the gut. Here, we analyzed the whole genomes of 12 B. moukalabense strains isolated from seven feces samples of wild western lowland gorillas (Gorilla gorilla gorilla), three samples of wild central chimpanzees (Pan troglodytes troglodytes) and two samples of wild forest elephants (Loxodonta cyclotis) in Moukalaba-Doudou National Park, Gabon. In addition, we analyzed the fecal bacterial communities of six wild western lowland gorillas by meta 16S rRNA gene analyses with next generation sequencing. Although the abundance of the genus Bifidobacterium was as low as 0.2% in the total reads, a whole genome analysis of B. moukalabense suggested its contribution digestion of food and nutrition of frugivore/folivore animals. Specifically, the whole genome analysis indicated the involvement of B. moukalabense in hemicellulose degradation for short chain fatty acid production and nucleic acid utilization as nitrogen resources. In comparison with human-associated Bifidobacterium spp., genes for carbohydrate transport and metabolism are not conserved in these wild species. In particular the glycosidases, which are found in all 12 strains of B. moukalabense, were variably detected, or not detected, in human-associated species.

Changes in Livelihood Practices, Strategies and Dependence on Bushmeat in Two Provinces in Gabon

Traditional, forest resource-dependent livelihoods face multiple challenges. In Gabon, bushmeat provides food and income for rural communities. This study investigates how villagers believe livelihood practices and dependence on bushmeat changed over the last decade and if alternative income and food generating strategies can be sustainable. Our results show that remote villages near Moukalaba Doudou National Park hardly changed practices. Less remote villages near Tchibanga experienced declining hunting revenues and are switching to alternatives. Villages near Libreville almost completely changed strategies, and are no longer dependent on forest resources. Changes in livelihood practices were driven either by resource depletion or urbanization. The ability to change depended on proximity to facilities and infrastructure. Although most respondents were able to change, not all alternative strategies are sustainable. The results highlight the need to evaluate the long-term effectiveness of alternative poverty reduction and nature conservation strategies in a context of urbanization and food security. There is a need to reduce bushmeat demand, making supply more sustainable through effective resource governance and creating a conducive institutional and policy environment.

Molecular Screening of Trypanosoma spp. in Glossina, Stomoxys and Tabanids in the Moukalaba Doudou National Park (South-West, Gabon)

Studies on the knowledge of the pathogens responsible for trypanosomosis remain insufficient in Gabon, particularly in protected areas, such as the Moukalaba Doudou National Park (MDNP). In order to uphold ecotourism in the Moukalaba Doudou National Park (MDNP), an entomological and parasitological study was carried out during the rainy season, from February to March 2017, to identify the trypanosome species harbored by tsetse, stable fly and tabanid vectors in this protected area. Fly collection was carried out using Vavoua and Nzi traps. Trypanosome infections in the flies were detected using the polymerase chain reaction (PCR). In total, seven species of tabanids, five species of tsetse flies and two species of stable flies were collected. These vectors harboured six species of trypanosomes, namely Trypanosoma simiae Tsavo (48%), T. theileri (17%), T. simiae (14%), T. brucei s.l. (10%), T. congolense (9%) and T. vivax (2%). The trypanosome infection rate (IR) varied somewhat among sites. It was 82% in the forest, 92% in settled areas and 95% in the savanna. The high prevalence of trypanosomes in this area raises the possibility of some trypanosomosis transmission risk to humans and animals, but the risk appears to be very low given the low frequency of T. brucei s.l. Studies on the blood meals typing could be done to identify sources and estimate the real risk of infection.

Novitates Gabonenses 89: Combretum longistipitatum Jongkind, sp. nov. (Combretaceae), a new liana species from Gabon

ABSTRACT The new species Combretum longistipitatum Jongkind, sp.nov. (Combretaceae) from Gabon is described and illustrated. This liana differs from other Combretum subgen. Combretum species by the exceptionally long stipe of the fruit compared to the size of the wings. The only location where the new species is known from is now part of Moukalaba-Doudou National Park.

Seasonal Change in Diet and Habitat Use in Wild Mandrills (Mandrillus sphinx)

Primates show various behavioral responses to resource seasonality, including changes in diet and habitat use. These responses may be particularly important for species living in large groups, owing to strong competition for resources. We investigated seasonality in diet and habitat use in wild mandrills (Mandrillus sphinx), which form some of the largest primate groups, in Moukalaba–Doudou National Park, Gabon. We used a fallen fruit census to measure fruit availability and camera trapping to measure visit frequency by mandrill groups on 11 line transects from January 2012 to November 2013, and collected mandrill feces for 25 months in 2009–2013 to assess their diets. Fruit availability varied seasonally, with a peak in December–February, and a scarce period in March–August. Relative volumes of fruit skin, pulp, and intact seeds in fecal remains varied with fruit availability, whereas feces contained as large a proportion of crushed seeds in the fruit-scarce season as in the fruit-peak season. The relative volumes of woody tissue (e.g., bark and roots) and the number of food types increased in the fruit-scarce season compared to in the fruit-peak season. Camera trapping revealed seasonality in habitat use. In fruit-rich seasons, mandrill visits were highly biased toward transects where fruit species that appeared in the majority of feces in a group were abundant. In contrast, in fruit-scarce seasons, visit frequencies were distributed more uniformly and the relationship with fruit availability was unclear. Our results suggest that mandrill groups in the study area respond to seasonal fruit scarcity by consuming seeds and woody tissue and by ranging more widely than in fruit-rich seasons. These flexible dietary and ranging behaviors may contribute to the maintenance of extremely large groups in mandrills.

How many species and under what names? Using DNA barcoding and GenBank data for west Central African amphibian conservation.

Development projects in west Central Africa are proceeding at an unprecedented rate, often with little concern for their effects on biodiversity. In an attempt to better understand potential impacts of a road development project on the anuran amphibian community, we conducted a biodiversity assessment employing multiple methodologies (visual encounter transects, auditory surveys, leaf litter plots and pitfall traps) to inventory species prior to construction of a new road within the buffer zone of Moukalaba-Doudou National Park, Gabon. Because of difficulties in morphological identification and taxonomic uncertainty of amphibian species observed in the area, we integrated a DNA barcoding analysis into the project to improve the overall quality and accuracy of the species inventory. Based on morphology alone, 48 species were recognized in the field and voucher specimens of each were collected. We used tissue samples from specimens collected at our field site, material available from amphibians collected in other parts of Gabon and the Republic of Congo to initiate a DNA barcode library for west Central African amphibians. We then compared our sequences with material in GenBank for the genera recorded at the study site to assist in identifications. The resulting COI and 16S barcode library allowed us to update the number of species documented at the study site to 28, thereby providing a more accurate assessment of diversity and distributions. We caution that because sequence data maintained in GenBank are often poorly curated by the original submitters and cannot be amended by third-parties, these data have limited utility for identification purposes. Nevertheless, the use of DNA barcoding is likely to benefit biodiversity inventories and long-term monitoring, particularly for taxa that can be difficult to identify based on morphology alone; likewise, inventory and monitoring programs can contribute invaluable data to the DNA barcode library and the taxonomy of complex groups. Our methods provide an example of how non-taxonomists and parataxonomists working in understudied parts of the world with limited geographic sampling and comparative morphological material can use DNA barcoding and publicly available sequence data (GenBank) to rapidly identify the number of species and assign tentative names to aid in urgent conservation management actions and contribute to taxonomic resolution.

Identification and molecular characterization of novel primate bocaparvoviruses from wild western lowland gorillas of Moukalaba-Doudou National Park, Gabon

Bocaparvoviruses have been studied extensively owing to their ability to cause respiratory illness or gastroenteritis in humans. Some bocaparvoviruses have been detected in non-human primates (gorillas and chimpanzees), but the diversity and evolution of these viruses are not fully understood. In this study, we collected 107 fecal samples from wild western lowland gorillas in Moukalaba-Doudou National Park in Gabon to investigate the presence of bocaparvoviruses. Using a combination of pan-bocaparvovirus PCR and individual identification by microsatellite genotyping, we found that two samples from two apparently healthy infant gorillas were positive for bocaparvovirus. Sequencing and phylogenetic analyses revealed that the two gorilla bocaparvovirus strains are nearly identical and are closely related to viruses in the species Primate bocaparvovirus 2 (with 86.0% nucleotide identity to a human bocavirus 2 isolate). To our knowledge, this is the first report showing the presence of a non-human primate bocaparovirus within Primate bocaparvovirus 2. Our findings provide novel insights into the diversity and evolution of bocaparvoviruses and highlight the importance of surveying these viruses for the safe management of gorilla-based ecotourism.

Vegetarian diet in Guenon and Mangabey monkeys of Moukalaba-Doudou National Park, Gabon: similarities and differences

To order to know any differences and similarities between Mangabeys and Guenons study of their vegetarian diet was conducted for 10 months between 2013 and 2014 in Moukalaba-Doudou National Park, Gabon. By using the direct observation method, we identified 84 plant species integral to the vegetarian diet of these two groups of monkeys. Thus, we have recorded similarities and differences. Guenons (69 species) consume the same plant species as the Mangabeys (49 species; V = 1594 p-value = 0.1796). They are considered frugivores at large because they consume an average of 84.77% fruit for guenons and 63.37% for the mangabeys, with a difference in the consummation of seeds 18.93% and 3.31% respectively. These results suggest that Mangabey have a seed-eating regime while the guenons tend to consume even when they are unavailable fruits. Our analyzes also showed that these two groups have preference different family of the species that they consume. This is due to the nature of the fruit produced by each family. Furthermore the mangabey (chi-squared = 5.6989, df = 5, p-value = 0.3366) interested in several of plants while monkeys (chisquared = 15.817, df = 5, p-value = 0.007387) remain more attached to fruit consumption.© 2016 International Formulae Group. All rights reserved.Keywords: Mangabeys, Guenons, diet, Moukalaba-Doudou, difference and similarity

Associations of ant species to land cover types and human disturbance in south‐west Gabon

We recorded ground-foraging ant species in forest and savannah habitats along a 52-km-long road planned for upgrade in the buffer zone of the Moukalaba-Doudou National Park in south-west Gabon. Sixty stations were established with three sampling points on each side of the future road and baited with peanut butter to record the presence of invasive Wasmannia auropunctata (Roger, 1863). We documented 46 ant species including one genus and eight species not previously reported in Gabon, but no evidence of the presence of W. auropunctata. We also found species known to have an opportunistic behaviour such as Cardiocondyla emeryi (Forel, 1881), Tetramorium simillimum (Smith, 1851) and Trichomyrmex destructor (Jerdon, 1851). Species richness in forested stations was significantly higher than in savannah. Among the most common ant species in the area, we identified 13 associated with forests, eight associated with savannahs and one generalist. Four species were highly tolerant to human disturbance. Our study, even if biased towards stress-tolerant species, provides new insights about ant species associations with habitats and contributes to the establishment of a reference system to classify African ant species that could be used to monitor the success of restoration of areas impacted by human activities.

Molecular features of hookworm larvae (Necator spp.) raised by coproculture from Ugandan chimpanzees and Gabonese gorillas and humans

Species composition of Necator hookworms was surveyed in (i) Ugandan chimpanzees living around farms and villages at Bulindi, (ii) Gabonese gorillas under habituation in Moukalaba-Doudou National Park (MDNP), and (iii) Gabonese villagers living adjacent to MDNP. Internal transcribed spacers (ITS) of rDNA and partial cytochrome c oxidase subunit 1 (Cox1) gene of mtDNA were analyzed from larvae obtained by coproculture. Three ITS types (I, II and III) and three Cox1 haplotype groups (A, B and C) were demonstrated. ITS type I and Cox1 haplotype group A, representing Necator americanus, were demonstrated in the hookworm larvae from Gabonese gorillas and humans, but not from Ugandan chimpanzees. Type II and haplotype groups B and C, presumably representing N. gorillae, were found in larvae from Ugandan chimpanzees and Gabonese gorillas and humans. These features were overall similar with those found previously in the Central African Republic. Meanwhile, type III was proven in a larva from a Gabonese gorilla as the first demonstration from a non-human primate. Cox1 haplotypes obtained from Ugandan chimpanzees formed a subgroup within group B, presumably reflecting dispersal and diversification processes of the apes.

Epidemiological study of adenovirus infecting western lowland gorillas and humans in and around Moukalaba-Doudou National Park (Gabon)

Epidemiological study of adenovirus infecting western lowland gorillas and humans in and around Moukalaba-Doudou National Park (Gabon)

Molecular epidemiological study of adenovirus infecting western lowland gorillas and humans in and around Moukalaba-Doudou National Park (Gabon).

Adenoviruses are widespread in human population as well as in great apes, although the data about the naturally occurring adenovirus infections remain rare. We conducted the surveillance of adenovirus infection in wild western lowland gorillas in Moukalaba-Doudou National Park (Gabon), in order to investigate naturally occurring adenovirus in target gorillas and tested specifically a possible zoonotic transmission with local people inhabiting the vicinity of the park. Fecal samples were collected from western lowland gorillas and humans, and analyzed by PCR. We detected adenoviral genes in samples from both gorillas and the local people living around the national park, respectively: the overall prevalence rates of adenovirus were 24.1 and 35.0 % in gorillas and humans, respectively. Sequencing revealed that the adenoviruses detected in the gorillas were members of Human mastadenovirus B (HAdV-B), HAdV-C, or HAdV-E, and those in the humans belonged to HAdV-C or HAdV-D. Although HAdV-C members were detected in both gorillas and humans, phylogenetic analysis revealed that the virus detected in gorillas are genetically distinct from those detected in humans. The HAdV-C constitutes a single host lineage which is compatible with the host-pathogen divergence. However, HAdV-B and HAdV-E are constituted by multiple host lineages. Moreover, there is no evidence of zoonotic transmission thus far. Since the gorilla-to-human transmission of adenovirus has been shown before, the current monitoring should be continued in a broader scale for getting more insights in the natural history of naturally occurring adenoviruses and for the safe management of gorillas’ populations.Electronic supplementary materialThe online version of this article (doi:10.1007/s11262-016-1360-8) contains supplementary material, which is available to authorized users.

Female Reproductive Seasonality and Male Influxes in Wild Mandrills (Mandrillus sphinx)

The correlates of variation in the number of males in primate groups form a long-standing question in primatology. We investigated female reproductive seasonality and the numbers of males in groups of wild mandrills (Mandrillus sphinx) in a 25-month camera-trap survey with 160 camera locations in Moukalaba-Doudou National Park, Gabon. We used 1760 videos to analyze group composition, including the presence of females with newborn infants and with sexual swellings, the number of males present in groups, and male spatial positioning in groups. Female reproduction was seasonal, with a peak in the number of newborns in the mid-rainy season and a peak in the number of females with sexual swellings in the early dry season. The number of males in the group increased in the dry season, with a much greater increase in the number of mature males (sevenfold) than in submature males (twofold). The peak number of mature males, but not submature males, in the group lagged significantly behind the peak in the number of females with sexual swellings, suggesting that submature males enter groups before mature males and/or that mature males stay in the group longer after the peak of females with sexual swellings. Mature, but not submature, males appeared frequently near females with sexual swellings. In conclusion, we found a clear relationship between the presence of receptive females and the number of males in the group, and evidence that male competitive ability influences male strategies.

Estimating diurnal primate densities using distance sampling method in Moukalaba-Doudou National Park, Gabon

Objective: To complete data of diurnal primates, we have estimated the density of diurnal primates in the northeastern part of Moukalaba Doudou National Park (MDNP) in Gabon and then we compared the results from those obtained in other areas. Methodology and results: we estimated the densities of each species based on the conventional distancesampling approach. Sampling was done in two sessions along 14 line-transects including various types of vegetation. Cercocebus torquatus is the species most abundance with 62.37 ind.km -2 , followed by Cercopithecus nictitans (33.26 individuals.km -2 ), Cercopithecus cephus (29.38 individuals.km -2 ) Lophocebus albigena (15.72 ind.km -2 ). The low density was observed in Cercopithecus pogonias (5.23 individuals.km -2 ). Those values are higher than Makokou with C. cephus , C. nictitans 25 ind.km -2 and 30 ind.km -2 respectively. Those results are relatively high unlike to Lope C. cephus (5.1 individuals.km-2) C. nictitans (19.2 individuals.km-2) C. pogonias (4.6 individuals.km -2 ) which have the same vegetation types. They are different from Loango Loango, C. cephus (13.33 individuals.km -2 ) C. nictitans (3.71 individuals.km -2 ) Cercocebus torquatus (15.89 individuals.km -2 ) which have a disturbed forest, which may affect monkey’s density. Conclusion and application: our results showed that the density of monkeys in MDNP is among the highest in Gabon. This can be explained by the lacking of colobine monkeys, which generally dominated in the African rainforest, and the different types of vegetation that we founded. Keywords: Moukalaba-Doudou, distance sampling, monkeys, density, comparison