The development of roads in eight African countries is causing the chimpanzee population density to consistently drop.
This is according to new research published in Conservation Letters, a journal of the Society for Conservation Biology.
The researchers examined the effect of major and minor roads on the West African chimpanzee numbers in Ghana, Guinea, Guinea Bissau, C’ôte d’Ivoire, Liberia, Mali, Senegal and Sierra Leone.
The West African or western chimpanzee population, which is classified as critically endangered has declined 80% in the past 20 years. As the human population grows, the chimpanzees face mounting pressure from the expansion of infrastructure and settlements.
Researchers from University of Exeter, together with a team of researchers from Concordia University and the Potsdam Institute for Climate Impact Research, used the ecological threshold analysis to quantify the road-effect zone for the critically endangered species. The results were “shocking”, according to the researchers.
“Roads have a negative impact on chimpanzee populations that can extend for more than 17km,” the researchers found. “The impacts extended to an average of 17.2km from major roads, and 5.4km from minor roads.”
Across the present geographic range of the West Africa chimpanzee, covering 528 010km, there are 41 925km of major roads and 206 110km of minor roads.
The researchers’ analysis shows that the chimpanzees are harmed by roads across 95.7% of their present geographic range and, with just 4.3% of their range unaffected, they have nowhere else to go.
Although the study did not look at the reasons roads affect chimpanzee numbers, the researchers highlighted some of the possible explanations. These included road kills and industries such as mining and agriculture, which often reduce or remove forest habitats.
“Roads can also restrict chimpanzee movements, dividing populations and causing genetic isolation,” said the researchers.
“Hunting is a persistent threat to western chimpanzees, and roads provide easier access for hunters.”
The researchers suggested that strategies be implemented to ensure that road projects adhere to the International Finance Corporation’s best practice guidelines.
The implementation of long-term, large-scale monitoring of legal and illegal resource extraction, including logging, mining, and hunting along the length of the road is critical.
Other interventions proposed include the installation of roadblocks to inspect vehicles for illegally acquired forest resources; the removal of snares; and the installation of road bumps, implementation of speed limits with clear signage, and the reduction of road width to reduce vehicles’ speed.