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. 2024 Jul 24;14(7):e70080.
doi: 10.1002/ece3.70080. eCollection 2024 Jul.

Ecological correlates of chimpanzee termite fishing behavior in Mbam & Djerem National Park, Cameroon

Affiliations

Ecological correlates of chimpanzee termite fishing behavior in Mbam & Djerem National Park, Cameroon

Tyler C Andres-Bray et al. Ecol Evol. .

Abstract

Chimpanzee insectivory is seasonally variable, with pronounced peaks or set seasonal periods of consumption observed in most chimpanzee communities. This variation is interesting given that chimpanzees invest considerable effort into complex tool-using behaviors to acquire insect prey. Evidence suggests this seasonal variation is related to insect behavior, but few studies have been done to empirically examine this relationship. In this study, we assessed whether a seasonal pattern of termite fishing by Nigeria-Cameroon chimpanzees (Pan troglodytes ellioti) in Mbam & Djerem National Park, Cameroon was driven by termite behavior. We measured termite presence and termite foraging activity monthly at seven termite mounds near Ganga Research Station from April 2022 to April 2023. Macroscopic fecal analysis and camera traps placed at each mound demonstrated termite fishing in this community occurred from March to June, with a rare smaller period of termite fishing in October 2021. Average monthly rainfall, average monthly temperature, and average monthly fruit availability were used to examine potential environmental factors that could impact termite fishing seasonality. Termite presence was significantly different between months with and without chimpanzee termite fishing (t-test, -6.569, p < .001). Termite presence was also significantly associated with average monthly rainfall (ANOVA, F = 13.9, p = .002, R 2 = .775). Termites in this region appear to respond to the transition from dry to wet seasons by moving closer to the soil surface. This corresponds with greater chimpanzee termite fishing, suggesting that termite accessibility may be driving seasonal variation in this behavior.

Keywords: Nigeria‐Cameroon chimpanzee; seasonality; termite behavior; tool use.

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Conflict of interest statement

The authors declare that they have no known competing financial interests, personal relationships, or other involvements that could have influenced or raised questions of bias in the work reported in this paper.

Figures

FIGURE 1
FIGURE 1
Seasonal breakdown of Mbam & Djerem National Park based on rainfall and temperature. The dry season occurs generally from approximately November to February. The wet season can be split into the small rainy season from March to June, and the big rainy season from July to October. The small rainy season is a transitionary season marked by steadily increasing rainfall and high average temperatures, while the big rainy season has high average rainfall and low average temperatures. Error bars for rainfall line represent standard error. Data for this figure were acquired from 1991 to 2020 from the Climate Research Institute.
FIGURE 2
FIGURE 2
Location of termite mounds along transects near Ganga Research Station: Ganga Research Station is found in the northeastern part of Mbam & Djerem National Park, which is located in both the Adamawa and Centre regions of central Cameroon. Since 2016, monthly biomonitoring has been conducted along 10 2‐km‐long transects that extend perpendicular to the Djerem river at 0.5 km intervals. The red and black dots represent termite mounds where camera traps were placed. Red dots are mounds where chimpanzees have been seen on camera termite fishing while black dots are mounds where we captured no video evidence of chimpanzee termite fishing. Termite mounds where chimpanzee termite fishing was observed are assumed to be Sphaerotermes sphaerothorax based on comparative abundances of termite specimen identified via morphological characteristics, though this is not definitive (See Section 2.2.2 for further information). Purple, green, and orange areas in the map represent genetically distinct populations of chimpanzees from Mitchell et al. (2015): Two P. t. ellioti populations in a rainforest habitat (purple) and ecotone habitat (green), and one population of P. t. troglodytes (orange).
FIGURE 3
FIGURE 3
Temporal variation in consumption of mound‐building termites near Ganga Research Station. This graph shows the number of camera trap videos depicting termite consumption per month of chimpanzees (Pan troglodytes ellioti) as well as several known termite specialists: (1) Giant pangolin (Smutsia gigantea), (2) Tree pangolin (Phataginus tricuspis), (3) Aardvark (Orycteropus afer), and (4) African civet (Civettictis civetta). This demonstrates a pattern across all of these species of prolonged termite consumption in the early half of the year with a spike in activity around March–June, and a smaller secondary period of termite consumption around October/November that is seen primarily in the termite specialists. It is important to note that all videos of chimpanzee termite fishing that occurred in October during the 3‐year course of this project were a single fishing event by a single chimpanzee.
FIGURE 4
FIGURE 4
Diagram of termite foraging activity data collection. Termite foraging activity was measured monthly using 10 cellulose baits composed of toilet paper, with half being buried underground and half being secured to the soil surface using a modified stick. Together, these baits encircled each mound and were replaced monthly. Baits secured to the surface were covered with plastic bags to prevent wear from environmental factors. The above photograph includes examples of baits at various levels of consumption and an example set‐up at one of the termite mounds surveyed in this study.
FIGURE 5
FIGURE 5
Diagram of termite presence data collection and soil sample collection. Termite presence in the soil surface was measured through active searching in five 1 m × 1 m quadrats tangent to each termite mound. Five 6‐inch‐deep holes were dug in each quadrat (light gray circles) and the level of termite presence was quantified for per quadrat. Every two months, two soil samples were collected from each mound (dark gray circles), one from the apex and one from the base.
FIGURE 6
FIGURE 6
Assessment of cellulose bait scores. The figure on the left shows the relationship between number of termites found per bait during collection and the activity score for that bait. The figure on the right shows the same information for all nontermite arthropods found in each bait. Overall, far more termites were seen per bait than other arthropods, and the number of termites in each bait had a better goodness of fit with the bait score compared to nontermite arthropods (Termites: R 2 = .315, Nontermite Arthropods: R 2 = .164), suggesting that termites are more responsible for bait consumption than other insects.
FIGURE 7
FIGURE 7
Fruit availability distribution between seasons. This figure shows the average monthly fruitfall of preferred chimpanzee fruits at Ganga Research Station using biomonitoring data from 2016 to 2021. The average monthly fruitfall was determined using the mean of each month's number of fallen fruits observed along the 10 2 km transects near Ganga Station. Preferred fruits represent the 10 most commonly found fruit species in chimpanzee fecal samples in this area. Preferred fruits are more available in the small rainy season (March to June) and the big rainy season (July to October) compared to the dry season (November to February) (F = 3.378, p = .081). Significance values represent the following: *p < .05, **p < .01, ***p < .001, ns = non‐significant.
FIGURE 8
FIGURE 8
This figure shows the average monthly termite presence score per season from April 2022 to March 2023. The average monthly termite presence score was calculated by taking the sum of termite presence scores from each quadrat and calculating the mean of those summed scores each month across all seven termite mounds. Termite presence in the soil surface was significantly greater during the small rainy season (March–June) compared to the other two seasons (F = 14.48, p = .002). Significance values represent the following: *p < .05, **p < .01, ***p < .001, ns = non‐significant.
FIGURE 9
FIGURE 9
Termite foraging activity score distribution between seasons. This figure shows the average monthly termite activity score per season from April 2022 to March 2023. The average monthly termite activity score was calculated by calculating a corrected termite activity score for each termite bait using a regression equation relating the assigned bait score with the number of termites found per bait. These corrected scores were then summed across all baits per mound and then we calculated the mean of these summed corrected scores each month across all seven termite mounds. Termite foraging activity was not significantly different between each season (F = 0.699, p = .525). Significance values represent the following: *p < .05, **p < .01, ***p < .001, ns = non‐significant.
FIGURE 10
FIGURE 10
Bimonthly variation in pH and water content of termite mound soil. These figures show the distribution monthly values of mound soil pH (a) and water content (b) from June 2022 to February 2023 for the seven termite mounds monitored during this project. The pH of the termite mound soil remained relatively consistent throughout the year with a slightly acidic mean value of approximately 6.5. Water content was more variable, with the highest water content seen in June at the transition from the small rainy season to the big rainy season, and the lowest water content was observed in February during the dry season.
FIGURE 11
FIGURE 11
Ecological correlates of chimpanzee termite fishing seasonality. These figures show the differences in mean monthly termite presence in the soil surface (a), mean monthly termite foraging activity (b), mean monthly temperature (c), mean monthly precipitation (d), and mean monthly availability of preferred fruits (e) between months when chimpanzees have and have not been known to participate in termite fishing. MM in the figure axes denotes “mean monthly.” Termite presence in the soil surface was significantly higher during periods when chimpanzees would participate in termite fishing compared to periods when they did not (t = −6.569, df = 7.245, p < .001). All other ecological variables were not significantly different relative to when chimpanzees fished for termites (termite foraging activity: t = −1.259, df = 6.318, p = .252; mean monthly temperatures: t = −1.781, df = 8.315, p = .111; mean monthly precipitation: t = −1.135, df = 6.668, p = .295; mean preferred fruit availability: t = −1.259, df = 9.921, p = .237). Significance levels represent the following: *p < .05, **p < .01, ***p < .001, ns = non‐significant.
FIGURE 12
FIGURE 12
Ecological correlates of termite presence in the soil surface. These figures show the relationship between mean monthly termite presence score and mean monthly temperature (a) and mean monthly rainfall (b). The relationship between mean monthly rainfall and mean monthly termite presence score showed a much greater correlation compared to that with mean monthly temperature (mean monthly temperature: R 2 = .270; mean monthly rainfall: R 2 = .775). This suggests that rainfall is a very strong predictor of termite presence in the soil surface.

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