The Douala-Eéa National Park, formerly known as the Douala-Edéa Wildlife Reserve, is a protected area in Cameroon. It is located in the Littoral region, within the Sanaga Maritime department. Covering an area of approximately 2630 km², it stretches along the Atlantic coast south of Douala for about 35 km to the Dipombé River. It is geographically located at 3˚30'00''N, 9˚49'60''E. Tissongo Lake, a lagoon connected to the southern bank of the Sanaga River by a five-kilometer tidal channel, is included in the reserve. This area of state public land, designated for wildlife conservation, encompasses the localities of Mouanko, Edéa, Dizangué, and the Manoka Islands. The park is bordered to the north by the southern suburbs of Douala, to the south by Kribi, and to the west by the Atlantic Ocean [32], as shown in Figure 1.

Field surveys were conducted between March and June 2024, corresponding to the early rainy season in Littoral Cameroon. Prior to selecting the technique for identifying habitat structures and evaluating the impact of human activities on chimpanzee habitat use, a reconnaissance survey was carried out with the assistance of local hunters identified by village chiefs. This preliminary survey provided information on potential chimpanzee locations within the park. Coordinates of these sites were recorded on data sheets and later imported into Quantum GIS (QGIS). Using a digital map of Douala-Edéa National Park obtained from the Protected Planet database, reccetransect positions were systematically established.

A grid system of 2 km was created across the study zone. Within each grid, a 1 km recce-transect was positioned, spaced 1 km apart, ensuring coverage of different vegetation types (Figure 2). Each transect was defined by a starting point (A) and an ending point (B), with a line drawn between them to cut across multiple habitat types. In total, 31 recce-transects were established, representing the diversity of ecosystems within the sampling zone. Coordinates of transects (points A, B, and the transect line) were uploaded into a Garmin 64 GPS to facilitate navigation during fieldwork.

Figure 1.Location map of Douala-Edéa national park.

Detection probability was not formally estimated; however, observer consistency, standardized sign identification, and GPS recording minimized bias. GPS track logs were activated during transect walks to avoid double counting signs, considering that multiple signs could originate from the same individuals.

During the main survey, all 31 reccetransects were systematically traversed once. While transects were designed as straight lines, in practice they were followed opportunistically—using hunter and animal trails where available, or cutting through vegetation with machetes when necessary. This approach ensured coverage of different vegetation types and reduced the risk of double counting. Data collection began at point A and continued toward point B.

Chimpanzee presence signs included both direct sightings and indirect evidence such as vocalizations, feeding traces (fruit remains, nut-cracking sites), nests (fresh, recent, old, degraded), dung (fresh, recent, old, very old), and tracks. Anthropogenic signs recorded included snares, farms, logging activity, and settlements. All signs were documented opportunistically along transects. The total sampling effort amounted to 31 kilometers, corresponding to the 31 reccetransects surveyed during the rainy season (Figure 2).

Figure 2. Map showing the data collection zone in the Douala-Edéa National Park.

In the field, each observation—whether a chimpanzee presence sign or an anthropogenic indicator—was systematically assigned to a habitat class and canopy category. Habitat types were classified according to vegetation structure and land use. For example, primary forest was defined as undisturbed, mature forest with a closed canopy; secondary forest as regenerating areas with mixed successional vegetation; farm-forest mosaics as zones where agricultural plots were interspersed with remnant forest patches; and liana forest as areas dominated by vines.

Canopy cover was visually estimated by trained observers within a 20-meter radius of each observation point. Categories included: Closed canopy (>70% cover), Semi-open canopy (40% - 70% cover) and Open canopy (<40% cover). Each observation was georeferenced using GPS coordinates and immediately assigned to the appropriate habitat class based on the dominant vegetation type at the location. This systematic approach ensured consistency across survey teams and minimized observer bias. However, not all quadrates were sampled during field inventory as shown in Figure 3.

Figure 3. Map showing the sampled and non-sampled quadrats.

Two teams of four people were formed. The principal investigator, equipped with a Garmin 64 GPS (for recording coordinates and following transect lines) and a Xperia XZ3 phone camera (for photographic documentation), was responsible for observing chimpanzee signs and anthropogenic signs and recording data on standardized sheets. An assistant carried a 12 × 42 binocular (for distant observations) and a compass (for orientation), and assisted in identifying signs. A local guide carried a machete to clear difficult paths and helped identify chimpanzee traces. A porter transported materials and food supplies and also contributed to animal identification. Chimpanzee signs were recorded through both direct and indirect observations, including nests, droppings, vocalizations, food remains, tools, and footprints. Signs of anthropogenic activities such as traps, tree stumps, cultivated fields, fishing nets, hunter camps, charcoal production sites, and other tools—were also documented along transects. Surveys were conducted during peak activity hours, between 6:00 - 10:00 am and 3:00 - 5:00 pm and each recce-transects was walked for approximately one hour.

Data analysis began with decoding the information recorded on field data sheets and GPS devices into a computer. Field data were first entered into Microsoft Excel 2013 and subsequently imported into R software (version 4.1.0) [33] for statistical analyses. Results were generated in the form of figures, curves, frequencies, and percentages.

Encounter rates (signs per kilometer) were calculated as the number of biological or anthropogenic indices divided by the total survey distance (31 km), representing the sampling effort. Statistical significance was set at a 5% probability threshold for all analyses.

Kendall’s rank correlation test was applied to assess the relationship between chimpanzee presence indices and altitude gradients. Kendall’s tau was selected because it is a non-parametric test suitable for ordinal data and small sample sizes, allowing robust assessment of monotonic relationships.

Habitat use analysis was based on the relative frequency of chimpanzee signs per habitat type, standardized by survey effort. The relationship between chimpanzee signs (dependent variable: occurrence, presence/absence, or counts) and anthropogenic signs (independent variable: intensity, measured as the number of human activity indicators per sampling unit) was assessed descriptively.

For cartographic outputs, coordinates of biological and anthropogenic indices recorded with a Garmin 64 GPS were exported into QGIS 3.20. This facilitated the production of maps, including the study area map, sampling map, spatial distribution of chimpanzee indices, and anthropogenic activity maps. To determine chimpanzee habitat types, Landsat 8 - 9 OLI/TIRS satellite imagery (November 2021) was downloaded from the USGS Earth Explorer (https://earthexplorer.usgs.gov/). The imagery was processed in ENVI 4.5 using an unsupervised classification strategy, grouping land use into three classes. Outputs from the classification were later integrated in QGIS to generate the final land cover map.

This section presents the habitat structures and compositions preferred by chimpanzees, including encounter rates of biological signs, canopy cover, slope, and the different habitat types observed.

3.1.1. Encounter Rates of Chimpanzee Biological Signs

During the surveys, a variety of biological signs of chimpanzees were identified, including nests, feces, vocalizations, tools, footprints, and food remains. The percentages and encounter rates of these signs were estimated. Table 1 summarizes the encounter rates of chimpanzee biological signs recorded in the study area. The results show that nests were the most frequently observed indicator, with an encounter rate of 0.87 signs/km (n = 27). In contrast, tools (0.06 sign/km; n = 2) and vocalizations (0.06 sign/km; n = 2) were the least represented.

Table 1. Encounter rates of chimpanzee biological signs.

Legend: ERC: Encounter Rate of Chimpanzee, sign/km: sign per kilometer.

3.1.2. Encounter Rates of Nests Based on Age

The nests encountered during the survey were categorized into four age classes: fresh nests, recent nests, old nests, and degraded nests. Table 2 presents the encounter rates of these nest types. The results indicate that degraded nests were the most frequently observed, with an encounter rate of 0.38 sign/km (n = 12), whereas fresh nests were the least observed, with an encounter rate of 0.06 sign/km (n = 2) in the study area.

Table 2. Encounter rates of nests based on age in the study area.

Legend: ERC: Encounter Rate of Chimpanzee, (%): Percentage, TDC: Total Distance Cover.

3.1.3. Types of Habitats and Altitudes Identified in the Study Area

The chimpanzee signs recorded during the surveys made it possible to distinguish between different habitat types and the altitudes preferred by chimpanzees. Table 3 presents the percentage of observations across habitat types and the average estimated altitudes in the study area. Results show that liana forests (0.32 sign/km) and primary forests (0.25 sign/km) had the highest encounter rates of chimpanzee signs, with average altitudes of 42 m and 54 m, respectively. However, leftover food (8 indices) and footprint (indices) were not included in this table since they could not be specifically be distinguish from other primates sharing the same habitats.

Table 3. Average altitudes and chimpanzee encounter rates by habitat type.

Legend: Number of Observations per Habitat (NOH), Percentage of Habitats (PH), Average Altitudes (AA), Number of Chimpanzee Signs Identified (NCSI), Percentage of Chimpanzee Signs (PCS), and Encounter Rate of Chimpanzee (ERC).

Statistical analysis revealed a significant association between the altitudinal gradient and the probability of encountering chimpanzee presence signs. The number of presence signs increased with altitude (Kendall’s tau = 0.51, p = 0.04), as illustrated in Figure 4.

3.1.4. Vegetation Cover in the Study Area

The frequencies of different canopy types were determined based on biological and anthropogenic signs recorded in each habitat type. Table 4 presents the percentages of canopy types by habitat. Results indicate that closed canopies were most common in liana forests (20%) and primary forests (12%). Sparse canopies occurred across nearly all habitats, but their percentages were very low in rivers (2%), swamps (5%), farms (5%), and secondary forests (5%). In contrast, open canopies were most prevalent in farms (21%), secondary forests (19%), and rivers (16%), while they were less frequent in primary forests and completely absent in liana forests (0%).

Figure 4.Significant association between the altitudinal gradient and the probability of encountering chimpanzee presence signs.

Table 4. Distribution of canopy types by habitat.

Legend: FCC: Frequency of Closed Canopies, (%): Percentage, FSC: Frequency of Sparse Canopies, FOC: Frequency of Open Canopies.

3.1.5. Spatial Distribution of Chimpanzee Signs in the Study Area

The coordinates of chimpanzee signs were imported into QGIS to produce a spatial distribution map (Figure 5). This map illustrates the distribution of chimpanzee presence across the study area. Using compass orientation, it was observed that the northern, northwestern, and southern sectors of the sampled area showed no evidence of chimpanzee presence. In contrast, the northeastern and southeastern sectors contained only a few observations. The eastern sector, together with several islands where chimpanzees have been reintroduced, recorded the highest concentration of signs, indicating localized habitat use and preference.

Figure 5. Map of spatial distribution of chimpanzee in Douala-Edéa national park.

3.1.6. Representation of Vegetation Cover and Land Use Map

A vegetation cover and land use map was developed to identify potential locations of chimpanzee-preferred habitats within the study area (Figure 6). This map was generated using Landsat 8 - 9 OLI/TIRS satellite imagery (November 2021) to classify land cover and land use. The results indicate that the study area is predominantly composed of primary forest, which surrounds the liana forests—the habitats most strongly preferred by chimpanzees. These areas represent the most critical zones for targeted conservation efforts, as they provide essential ecological conditions for chimpanzee survival and habitat use.

Figure 6. Vegetation cover and land use map of Douala-Edéa national park.

3.2.1. Encounter Rates of Anthropogenic Signs

Within study area, several anthropogenic signs were recorded, including illegal hunting (poaching), deforestation, and agricultural expansion (Table 5). The data indicate that hunting was the most prevalent activity, with an encounter rate of 3.7 sign/km (N = 115). This was followed by deforestation, which had an encounter rate of 2.06 sign/km (N = 64). The least observed activity was the use of fishing net, with an encounter rate of 0.06 signs/km (N = 2).

Table 5. Encounter rates of anthropogenic signs in the study area.

Legend: AA: Anthropogenic Activities, TRA: Encounter Rate of Anthropogenic Signs, %: Percentage.

3.2.2. Habitat Types Based on the Number of Encountered Anthropogenic Signs

The anthropogenic activities recorded during the surveys allowed for differentiation among the various habitat types. Table 6 shows that the highest encounter rate of anthropogenic activities occurred in secondary forests (3.29 sign/km; N = 102), followed by wooded forests (0.93 sign/km; N = 29) and fields (0.90 sign/km; N = 28). In contrast, encounter rates were very low in primary forests (0.32 sign/km; N = 10) and ravines (0.16 sign/km; N = 5).

Table 6. Habitat types based on anthropogenic activity signs.

Legend: Number of Observations per Habitat (NOH), Percentage of Habitats (PH), Anthropogenic Signs (AS), Percentage of Anthropogenic Signs (PAS), Encounter Rate of Anthropogenic Signs (ERAS) signs/km.

3.2.3. Spatial Distribution of Anthropogenic Activities

The coordinates of anthropogenic signs were imported into QGIS to generate a spatial distribution map (Figure 7). This map illustrates the extent and location of human activities within the study area. Compass orientation revealed that the northern, northwestern, and southern sectors of the sampled area exhibited the highest levels of anthropogenic activity. The northeastern and southeastern sectors showed moderate levels, while the eastern sector recorded low levels of activity.

Figure 7. Map of spatial distribution of anthropogenic activities in douala-edéa national park.

3.2.4. Influence of Anthropogenic Activities on Chimpanzee Signs Based on Their Preferred Habitats

During the ecological surveys, six types of chimpanzee presence signs were identified: food remains, vocalizations, footprints, tools, dropping and nests. The number of these presence signs (encounter rates) varied across habitat types. The highest encounter rates were recorded in the liana forest (N = 10) and primary forest (N = 8). In contrast, the lowest rates were observed in riparian zones, swamp forests, secondary forests, and raffia forests, while no presence signs were recorded in ravines. The greater number of presence signs in liana and primary forests may be attributed to the lower intensity of anthropogenic activities in these habitats, as illustrated in Figure 8. Conversely, the secondary forest, which exhibited the highest encounter rate of anthropogenic activities, showed relatively low numbers of chimpanzee presence signs (Figure 8).

Figure 8. Influence of anthropogenic activities on chimpanzee signs across habitat types.

Chimpanzee presence in Douala-Edéa National Park was highest in liana and primary forests, this because these forests may provide abundant fruiting trees, nesting opportunities, and structural cover, which together make them attractive habitats. For instance, findings by [19] in their studies in Kimbi Fungom National Park and the Kom-Wum Reserve, shows that the presence of chimpanzee signs were highest in primary and liana forests with minimal anthropogenic activities. This finding is consistent with studies in Mount Cameroon National Park, where canopy density and vegetation diversity were identified as key drivers of chimpanzee nesting ecology [18]. Similarly, research in Mbam-Djerem National Park found that nest abundance was strongly associated with dense canopy and higher altitudes [34]. The abundance of various tree species preferred by chimpanzees for nest construction plays a crucial role in their survival in the study area. A notable study by [35] in Kalinzu National Park, Uganda, examined the selection of trees for nest construction, showing that chimpanzees favor certain tree species due to their availability, branch structure (providing stability), and habitat positioning. Conversely, a study by [36] in Gabon found that while chimpanzees have preferences, they adapt to available resources when their habitat is disturbed. These habitat compositions and structures demonstrate that the study area provides favorable conditions for the preferred habitats of chimpanzees.

The significant positive correlation between altitude and chimpanzee presence signs (Kendall’s tau = 0.51, p = 0.040) suggests that higher altitude areas coincide with reduced human disturbance, which likely explains the greater frequency of chimpanzee signs there. Comparable results have been reported in other Central African forests, where chimpanzees select habitats that balance food availability and safety from human activity [9]. This highlights the importance of preserving habitats at higher altitudes to minimize human disturbances and promote chimpanzee presence. Additionally, chimpanzee nests were often found near watercourses and in areas with fruiting trees, facilitating their access to water and food. These observations are consistent with the findings of [10].

During the surveys, various biological signs were identified. Nests (0.87 signs/km) were the most represented indices, which aligns with the findings of [29], where nests were the most frequently observed signs. In areas of the study site where chimpanzee signs were found, the species preferred higher altitudes and dense canopies. This preference allows them to evade predators and shelter themselves from diverse climatic conditions, during different seasons. This observation aligns with the findings of [37] in Guinea, where chimpanzees were noted to prefer dense-canopy forests and areas with moderate altitudes for reasons of safety, access to food resources, and avoidance of anthropogenic pressure.

Closed canopies were most common in liana and primary forests, which corresponded with higher chimpanzee encounter rates. Sparse and open canopies, more frequent in farms and secondary forests, were associated with lower chimpanzee presence. This pattern reflects broader ecological findings that canopy closure provides protection and microclimatic stability, both critical for chimpanzee nesting and foraging [18].

Human activities were widespread, with hunting (3.7 signs/km) and deforestation (2.06 signs/km) being the most prevalent. This aligns with research conducted in Cameroon and Equatorial Guinea by [38], which indicates that poaching remains the primary threat to chimpanzees, particularly in the peripheral areas of national parks. These pressures mirror broader patterns across Cameroon, where bushmeat hunting and agricultural expansion are the primary drivers of chimpanzee decline [39][40]. Likewise, deforestation for agricultural expansion, charcoal production, logging, canoe-making, and fish smoking also contributes to the destruction of chimpanzee-preferred habitats in the study area. [19] reported similar anthropogenic activities disrupting chimpanzee habitats in Kimbi Fungom National Park and the Kom-Wum Reserve. Secondary forests, which had the highest rate of anthropogenic activities, showed very low chimpanzee presence, highlighting the direct negative impact of human disturbance. This finding is consistent with [41] in Sierra Leone, where chimpanzees avoid swampy and heavily degraded secondary forest areas due to human proximity and infrastructure (e.g., roads, industrial camps). Secondary forests, despite their high level of anthropogenic activity, had very few chimpanzee presence signs, likely due to the presence of fruit trees such as mangoes, bananas, and oil palms.

Spatial analysis revealed that chimpanzee signs were concentrated in the eastern sector and islands, areas with lower anthropogenic activity. In contrast, the northern, northwestern, and southern sectors showed high human activity and no chimpanzee presence. This spatial separation underscores the importance of intact forest refuges for chimpanzee survival, as also noted in studies of community attitudes toward primate conservation in Douala-Edéa [25].

This study faced certain constraints, including limited temporal coverage, reliance on indirect signs rather than direct observations, potential observer bias in habitat classification, and the absence of long-term monitoring that would strengthen projections for strategic conservation across the entire park. Nevertheless, the findings demonstrate that the overlap between preferred habitats (liana and primary forests) and areas of reduced human activity should be prioritized for conservation.

Effective strategies must integrate habitat protection, anti-poaching enforcement, and communitybased conservation initiatives. Such approaches are particularly critical given that local populations remain heavily dependent on forest resources and often reluctant to abandon hunting practices [42][43]. Strengthening these measures will not only support the longterm persistence of chimpanzee populations but also safeguard the broader ecological integrity of Douala-Edéa National Park.