In the jungles of the Central African Republic, a thin white string unfolds along the path of five wildlife researchers as they head deeper into the Dzanga-Sangha rainforest. For close to eight hours, the group inches their way forward, only moving as fast as a machete can hack away at an unforgiving terrain of thorns and vines.
As the team progresses along the transect, they collect samples of animal dung and document footprints, and occasionally install camouflaged cameras at key points of their journey.
The string trails behind as the group moves forward, marking the progress of their trek.This mile-long string represents one of 186 line transects being set up across the Dzanga-Sangha Protected Areas (DPSA) for the 2025 Wildlife Inventory overseen by Antoine Edé, DPSA’s head of monitoring, research, Primate Habituation, One Health and Forest Department.
Put simply, this is one of the ways that conservationists in the world’s second largest tropical rainforest count its wildlife populations.
The rainforests of the Congo Basin serve as a critical ecosystem for biodiversity and wildlife conservation. In Dzanga-Sangha, the work of surveying the populations of critically endangered wildlife is no simple endeavor.
“We’re doing conservation here, but we need to know what is happening, if it’s working, if it’s not working.” Edé said. “One way to know is if you just count the animals in the forest. But the question is, how do you count them?”
The World Wildlife Fund CAR and DPSA conduct the wildlife inventory every five years, providing a comprehensive survey of the number of wildlife populations within its over one million acres of dense wilderness.
The inventory is necessary for understanding the biodiversity of the region and for planning the distribution of eco-guard patrols, the law enforcement unit tasked with protecting wildlife from poachers and illegal hunting, according to Edé.
Analysis of previous wildlife inventories in Dzanga-Sangha have shown that the presence of eco-guards reduce human pressures and are critical for maintaining stable populations of these endangered mammal species. The value of the inventory is also to assess population trends of these endangered species over time. The last two inventories – in 2015 and 2020 – confirms that elephant and gorilla populations have remained stable, a sign that conservation efforts in Dzanga-Sangha are working.
Since 2010, DPSA has been primarily relying on the line transect and camera trap methods for the inventory, with a particular focus on monitoring large mammals such as western lowland gorillas, chimpanzees, forest elephants and bongos.
2025, the inventory started again. From February to October, DSPA will send out groups of six to conduct the survey at different sections of the forest. In the first visit, the group sets up the transect and the camera traps. Roughly a month later, the group returns for the second visit to assess the activity in that area through direct observations and camera footage.
Beyond the line transect and camera traps, this year, DPSA is experimenting with a new method of surveying wildlife: eDNA Elephant DNA, or genetic materials—like skin cells and mucus—left behind by species in their surroundings.
“We do it with leaf swabs,” Edé said. “The teams are just rubbing the swab on leaves at the center point of the transect. At the end, we extract these samples and we should be able to detect the species around us.”
“There may be a new way of doing this, which is good,” Edé said. “Now, we will have historical data because we are doing the line transect and the new method. And so we will both. We will be able to compare population size found with a transect, the population size found with a camera, and the population size found with DNA and see which method seems to be more accurate.”
However, the DSPA team is also concerned with the location and density of these groups and what that can tell researchers about human activity in the area.
“It’s more that the location of the elephants had changed,” Edé said. “They were more in the protected areas than outside of the protected areas… This can be translated as human activities are increasing in the community zones so the elephants are concentrating more in the national parks.”
For this inventory, Edé’s team is hoping that having four different methods to test against will help them to tell a more complete story about the wildlife of Dzanga-Sangha, including any risks or gaps in the conservation efforts. When the 2025 inventory concludes in October, Edé’s team will have the task of reviewing thousands of hours of camera footage, direct observations from the line transect, and eDNA samplings.
“So you see,” Edé said, “it’s a baseline to understand what is going on in the forest and how we should plan strategically the actions of everything [in Dzanga-Sangha].”
At the end of an hours-long inventory day, the team stumbles out of the forest, having just spotted a lone baby bongo in the forest only a few feet from the line transect at its finished point. This bongo represents just one of countless wildlife that will be observed by the time the 2025 inventory is complete.
