How Roads Hurt Chimpanzees

The negative impact can extend for more than 10 miles.

Western chimpanzee femalesusing rocks as tools
Western chimpanzee in Bossou Forest, Mont Nimba, Guinea. Anup Shah / Getty Images

When roads are built, they take away habitat from wildlife in the area. Animals are forced to move to find new homes—and sometimes the impact is far-reaching.

A new study finds that the negative effect of roads on wild chimpanzees can extend for more than 17 kilometers (10-plus miles).

Researchers investigated how roads of all types had an impact on the population of wild western chimpanzees in the eight African countries where the animals live.

They found that the effects extend an average of 17.2 km (10.7 miles) from major roads, and 5.4 km (3.4 miles) from minor roads. Average density of chimpanzee population peaked at the far limits of those areas and then was lowest nearest the roads.

The areas in the study were identified as “road-effect zones” (REZ). Less than 5% of the western chimpanzee’s range is outside of these zones.

The results were published in the journal Conservation Letters.

“Why we were interested in chimpanzees is a complex question,” Balint Andrasi, who led the study as part of a masters in Conservation Science and Policy at the University of Exeter, tells Treehugger.

“They are a charismatic megafauna and endangered, they are also our closest living relatives studying them provides a unique insight into our own evolution and behavior. They also have cultural significance in the countries they live in, but they themselves have culture too which should be protected.”

Chimpanzees were an ideal subject for the study because there is already a legal framework in place to protect them from roads, Andrasi says.

“Amending this framework with our results has real potential to do good for chimpanzees. So really, beyond anything else, I personally was looking for how relevant/how useful can this study be policy wise?” Andrasi says.

“Of course this does not mean that other great apes and other species should be ignored, in fact I am already thinking about what else could be done.” 

How Roads Are Threats

Chimpanzees crossing a road in Bossou, Guinea
Chimpanzees crossing a road in Bossou, Guinea.

Kimberley Hockings

Western chimpanzees are critically endangered with their numbers decreasing, according to the International Union for the Conservation of Nature (IUCN). Recent research has found that their population has declined by 80% in the past two decades.

Road building is one of the main threats. Roads cut into habitat and cause species fragmentation. When chimpanzees move and lose habitat and food, they may also forage on crops, causing farmers to kill or trap them in retaliation. Roads also make it easier for hunting, logging, and poaching.

Roads also affect a group’s ability to move in order to avoid violent skirmishes with other groups.

“Chimpanzees are highly territorial. Interactions with neighboring groups are often violent, even fatal,” Andrasi says. “Therefore it is not so obvious that a chimpanzee group would just move to a different area away from the disturbance. And when they stay, they are exposed to all sorts of impacts—some positive, but overwhelmingly negative.”

Chimpanzees mature late, in their early teens, and raise only one baby at a time. Because mothers keep their youngsters with them for a long time, they typically only have babies about every five years in the wild.

“And so the death of a few individuals from poaching, roadkill or disease can be devastating for a group,” Andrasi says. “Both two factors are key in making chimpanzees vulnerable to population decline and eventually extinction.”

Research Impact

The researchers hope their findings will help draw attention to the effects of roads and spur some changes to lessen their impacts.

“What we hope is that our REZ estimates are going to be used by relevant bodies (policy makers, development planners and conservationists) to better avoid or minimise road impacts on chimpanzees,” Andrasi says. 

"When roads appear, so do all sorts of human activities."

Many countries have regulations that require wildlife be considered before new roads are built. But this is the first time that the size of the area around roads has been estimated for its effect on chimpanzees, researchers say.

"The impact of infrastructure development is much larger than I ever anticipated and is truly worrying,” said Kimberley Hockings, of the Centre for Ecology and Conservation on the University of Exeter’s Penryn Campus, who also worked on the study.

"But we can’t give up. We must do everything we can to ensure their continued survival. I can’t imagine a world where humans are the only great apes left."

View Article Sources
  1. Andrasi, Balint, et al. "Quantifying the Road‐Effect Zone for a Critically Endangered Primate." Conservation Letters, 2021, doi:10.1111/conl.12839

  2. Balint Andrasi, who led the study as part of a masters in Conservation Science and Policy at the University of Exeter

  3. Humle, T. "Western Chimpanzee." IUCN Red List of Threatened Species, 2016, doi:10.2305/

  4. Evans, Thomas, et al. "The Mitigation Hierarchy in Environmental Impact Assessment and Related Legislation as a Tool for Species Conservation: A Case Study of Western Chimpanzees and Mining Development." Biological Conservation, vol. 261, 2021, p. 109237., doi:10.1016/j.biocon.2021.109237

  5. "Chimpanzee Society." Project R&R.

  6. "Roads Have Far-reaching Impact on Chimpanzee." University of Exeter.