Chimpanzees are nearing extinction in many countries. Of the four subspecies of these great apes, western chimpanzees are the most endangered. Experts estimate that their distribution is now extremely patchy, with 80% of their numbers having declined in the last 20 years. The largest-remaining population is found in the Ivory Coast in Western Africa, with smaller populations in Guinea, Sierra Leone, Nigeria, Guinea-Bissau and Liberia.
Poaching and habitat loss are some of the well-known threats to chimpanzees. But a study published last September finds that road developments are exacerbating their population decline. Noise pollution emanating from the construction of roads and poachers gaining access to more remote locations are some of the reasons to blame. A team of primate conservationists have quantified the extent to which roads jeopardize their communities. They say that just about 4.5% of the chimp population are left unaffected by roads.
On this episode of the Scienceline podcast, reporter Niranjana Rajalakshmi speaks with primate behavior experts who suggest a few strategies that could mitigate the impact of roads on western chimpanzees.
(Sounds of birds chirping and leaves rustling)
Niranjana Rajalakshmi: Chimpanzees are our closest living relatives. We share 99% of our DNA with them. But these incredibly intelligent animals are in danger. Especially the western chimpanzees that inhabit Western Africa, which are classified as “critically endangered” species, are threatened by habitat destruction, hunting and disease. But now, a new study says that roads have dramatically reduced western chimpanzee numbers.
But, how exactly do roads become a reason for the dwindling western chimpanzee population?
(Sounds of cars going on roads)
Tatyana Humle: The speed at which vehicles are traveling, we know that there have been examples of chimpanzees being killed on roads.
Niranjana Rajalakshmi: That’s Tatyana Humle, who teaches primate behavior at the University of Kent, U.K.
Tatyana Humle: Chimpanzees perceive roads as risky: They will wait alongside the road before crossing. They also have a particular way of crossing where the dominant male of the group will cross first and stop in the middle of the road and wait for all the other individuals to cross.
Niranjana Rajalakshmi: Humle says that the construction phase of the roads is a lot more disturbing to chimpanzees than the roads that have already been built.
Tatyana Humle: We’ve witnessed this in [Western] Africa, where a particular expansion of the width of a road with large machinery was actually very stressful and distressing for individual chimpanzees. So, they were screaming and vocalizing a lot and they were showing clear signs of distress.
(Sounds of chimpanzees screaming.)
Genevieve Campbell: So chimpanzees have territories that they defend. And so if they are pushed into another chimpanzee community, because of the disturbance or because of loss of habitat, then they will fight with other communities, which often leads to death of individual.
Niranjana Rajalakshmi: That’s Genevieve Campbell, who holds an important position in the International Union of Conservation of Nature’s task force, the role of which is to reduce the negative impact of infrastructure on great apes.
Genevieve Campbell: So if you remove habitat, they do have impact. It’s because you remove their resource to feed. There’s a lot of conservation effort to conserve and protect the population of the western chimpanzees and all throughout the range. And it’s been going on for several years. But often the budget is quite small in proportion.
Niranjana Rajalakshmi: Researchers like Campbell and Humle who study primate behavior worry that the problem is only getting worse in West Africa. But how much worse? That’s what Balint Andrasi, a research assistant at the Natural History Museum of Luxembourg wanted to find out.
Balint Andrasi: That realization of, of how big of an impact roads have – really shocking. They cannot tolerate hunting, for example, which is also associated with human presence and roads facilitate hunting.
Niranjana Rajalakshmi: For studying the impact of roads on chimpanzees, Andrasi and his team took an analytical approach. They used an open data source that stores the entire road network. They also downloaded the records of roads that are within the range of the western chimpanzees.
Balint Andrasi: I had that on a map. I had that for this entire geographical range. And on top of it, I put another source of information, which was a density distribution of chimpanzees that shows the distribution of chimpanzees within their entire range.
Niranjana Rajalakshmi: They then calculated something called the “road effect zone.”
Balint Andrasi: So, when you look at it you’ll see where the highest density of chimpanzees are, the lowest densities of chimpanzees are and anything in between.
Niranjana Rajalakshmi: What Andrasi and his team found was that the chimpanzees, as a community, try to avoid roads as much as possible and move farther away from them. And what’s shocking is that just less than 5% of the total land area that the chimps occupy is unaffected by the impact of roads.
As Andrasi was able to include a large area in his analysis, the impact of his study on primate conservation could be huge.
Balint Andrasi: We did this research on a scale that is over 500,000 square kilometers. We wouldn’t have been able to do it on foot.
Niranjana Rajalakshmi: But, with these results, what can be done to reduce this terrible impact of roads on the critically endangered western chimpanzee population?
Balint Andrasi: Our results could help avoid road effects by telling development planners how far away should they relocate the project, so that the chimpanzee population closest to the road is outside of the road effect zone.
Niranjana Rajalakshmi: But what about the existing roads or roads that have already been built? Andrasi suggests a few strategies for that.
Balint Andrasi: You need to know where you should put your roadblocks. You need to know where you should have your guard patrols to remove snares that trap chimpanzees or to monitor other human activities.
Niranjana Rajalakshmi: Humle has a few more suggestions to add.
Tatyana Humle: They have certain points where they will always cross the road. So these are kind of predictable spots. So, try and identify those and make sure that the traffic speeds are reduced in these points: signage with postings, raising awareness of people who frequently use these roads, maybe truck users.
Balint Andrasi: It’s not that we shouldn’t build roads. There are actually plenty of studies right now that focus on where [it is] optimal to build roads and where roads shouldn’t be built. When there is good intact forest landscapes, instead of always building new ones, we should find ways to connect already existing roads.
(Sounds of animals and birds in the forest)
Niranjana Rajalakshmi: For Scienceline, I’m Niranjana Rajalakshmi.
(Kalimba music fades)