The Gorilla Project Podcast: Episode #2

This article will give you a sneak preview of some stories we’re developing based on recent news reports and research papers.

Congo to Auction Land to Oil Companies

In the last episode of the Gorilla Project podcast, you heard the story of when a group of habituated chimpanzees attacked a group of gorillas in Loango National Park in Gabon. The chimps killed one infant gorilla during the first attack and ate another during the second attack. The episode starred the scientist Lara Southern, who witnessed both incidents and wrote the research paper “Lethal Coalitionary attacks of Chimpanzees on Gorillas in The Wild”. In it, she cited the Emma Bush paper explaining the attacks’ possible root cause. The Bush paper detailed how climate change was causing the lowest average daily temperature (in another national park in Gabon called Lopé) to rise by 0.25 degrees per decade. The trees in Lopé required the thermometer to fall below a certain threshold as a temperature cue to know when to produce fruit. Since the temperature had risen, the trees stopped knowing it was a fruiting season. As a result, researchers went from seeing approximately one in every ten trees with fruit in 1987 to only 1 in 50 fruit-bearing trees in 2018. Less fruit led to less food for frugivorous animals like elephants, gorillas, and chimpanzees. For example, the study stated that the body mass of the elephants in the park fell by 11 percent. The podcast argued that the same fruit shortage phenomenon witnessed in Lopé National Park might have caused increased food competition between chimps and gorillas in Loango National Park.

The public reaction to the episode leads to more questions

A post on Reddit linking to an article about this episode received over 1.4 million views. There was a lively discussion in the comments section in which people proposed counterarguments based on information they gleaned from the podcast. A few commenters seemed to need more clarification on the climate change findings in the Emma Bush paper, so we originally planned to follow Episode One with an episode based on her research and (hopefully) invite her to be a guest on the show.

Congo announces drilling

But then, on July 24, 2022, Ruth Maclean and Dionne Searcey released an article in the New York Times that attracted a great deal of attention titled “Congo to Auction Land to Oil Companies: ‘Our Priority Is Not to Save the Planet'”. The article’s subtitle read: ‘Peatlands and rainforests in the Congo Basin protect the planet by storing carbon. Now, in a giant leap backward for the climate, they’re being auctioned off for drilling.’ According to Searcey and MacLean’s article, the government of the DRC had planned to auction off vast amounts of land in and around the Congo River Basin to capitalize on the demand for fossil fuels. Many of you remember the film “Virunga,” which showed the trouble the rangers in the DRC’s Virunga National Park had fending off the oil companies who wanted to drill there. The New York Times article stated that the DRC government would auction oil and gas blocks affecting Virunga and the tropical peatlands. The forests and peatlands of the Congo River Basin store vast amounts of carbon. According to scientists, if they mine it for oil, they will release the carbon into the air and displace or kill the gorillas who live there.

Greenpeace predicts a global climate catastrophe

Greenpeace Africa describes the peatlands as “a biodiversity hotspot containing about 30 gigatons of carbon.” The article quoted Irene Wabiwa of Greenpeace in Kinshasa, saying, “If oil exploitation takes place in these areas, we must expect a global climate catastrophe, and we will all just have to watch helplessly.”

Congo reneges on their 10-year agreement

Eight months before making this decision, Congo’s president Félix Tshisekedi attended the global climate summit and endorsed a 10-year agreement to protect its rainforest. The deal included international pledges of 500 million dollars for Congo from the international community. Here’s a quote about the climate summit from the UN website describing this agreement:

“Through this new multi-year partnership, the DRC aims to first cap forest cover loss at its 2014-2018 average and ensure that deforestation continues to decline. The partnership will also promote the regeneration of 8 million hectares of degraded land and forests, and place 30% of national areas under a protection status, including areas where local communities undertake efforts to manage forests sustainably.”

They even signed a letter of intent. It had 12 concrete objectives. Let’s draw your attention to 3 of them:

# 1) High value forests, peatlands and community forest concessions are systematically incorporated into land-use plans, with the aim of maintaining the important role they play.

# 2) Transparency in natural resources governance is enhanced through the legal review of existing agriculture, logging, mine and oil concessions, the cancellation of illegal ones, as well as the publication of all contracts (linked to the Extractive Industries Transparency Initiative – EITI).

#3) New social and environmental standards are implemented to reduce the impact of mining and oil investments on forests and biodiversity, with reinforced measures in high value forests and peatlands. Any activity incompatible with conservation objectives in Protected Areas is BANNED.

According to the New York Times article, President Tshisekedi said the following at that summit:

“With its forests, water and mineral resources, the Democratic Republic of Congo is a genuine “Solution Country” to the climate crisis. To protect our forest and promote its sustainable management, our priority, backed by this new partnership, is to strengthen governance and transparency across all land use sectors.”

But then came the war in Ukraine. The European Union’s ban on Russian oil and natural gas resources made world leaders search for alternative places to source fossil fuels. For example, Norway has increased oil production and planned more offshore drilling; the US president visited the Saudis to ask that they increase the supply. It appears the DRC saw the shift in global sentiment towards fossil fuels as an opportunity to generate revenue.

Here’s a quote from the Mclean/Searcy article:

“And it raises a question asked by many communities whose very survival is based on cutting trees for sale or for cooking fires: If they protect carbon stocks of incalculable value to the whole world, what do they get in return?”

At least one DRC government official believes they should prioritize their needs against those of the planet. Tosi Mpanu, the DRC’s lead representative on climate issues and an adviser to the minister of hydrocarbons, said in an interview that their goal in auctioning off their rainforests for exploration was to raise money to reduce poverty. The New York Times article mentioned that the auction highlighted a double standard. Critics have asked: how can The West, which became wealthy by exploiting fossil fuels, demand that African countries refrain from doing the same? The article quoted Mpanu, the Congolese representative, saying, “Maybe it’s time we get to a level playing field and be compensated.”

The government posted an audacious video on Twitter announcing the auction. Despite the public outrage against the government’s decision, Congolese officials expanded the number of blocks up for auction from 16 to 30 (27 oil blocks and three gas). The post tagged Chevron and Total Energies. Total Energies claimed they didn’t intend to bid, but Chevron didn’t respond to a request to comment when the writers of the New York Times contacted them. Other significant oil producers also declined to comment.

With elections approaching, the article’s writers pointed out that the Congolese president needed to show he was doing something about poverty. The Congolese minister of hydrocarbon, Didier Budimbu, thought that the DRC could go from its current output of producing 25,000 barrels of oil a day to producing up to one million daily barrels. At current prices, that would pay out more than half of the DRC’s GDP.

The environmental consequences of oil exploration

Congolese officials didn’t know how much money they stood to make until they did seismic surveys. The article pointed out that the seismic survey process was already very destructive to the environment. The process would require trails to be cut into the rainforest and set off explosive charges. According to scientists: Oil exploration will poison their ecosystem with salt and heavy metals. It would also drain and dehydrate peatlands, leading to their decomposition and the release of the carbon trapped in them. According to Susan Page, a professor of physical geography at the University of Leicester in Britain, such a rapid release of carbon into the air could be the global climate tipping point. The road construction needed for the surveys will open previously uninhabited rainforest areas to loggers and poachers.

Dr. Simon Lewis is a professor of global change science at the University College London and the University of Leeds. Here are some quotes from a New Times opinion piece he wrote. He described the rainforest of the Congo River by saying: “It helps regulate our climate and slows climate change by removing 1.5 billion tons of carbon dioxide from the atmosphere each year.” He said, “In addition to accelerating the climate crisis, oil exploration here would be a pollution disaster for communities that depend on it and for wildlife.” He emphasized the importance of the peatlands by explaining,

“The peat stores colossal amounts of carbon, equivalent to three years’ worth of the world’s carbon emissions from fossil fuel use. Commercial hunters find reaching the waterlogged swamps difficult, so these peat swamp forests remain havens for wildlife. But oil prospecting requires the systematic cutting of thousands of miles of corridors to transport seismic survey equipment. If cut, these corridors will open up every part of the forest, with hunters and then illegal loggers following, dooming this natural sanctuary for wildlife.”

The Searcy and McLean article hinted that this auction might have been a ploy to attract more foreign aid. The writers gave the example of when Ecuador, in 2007, created a trust fund into which the international community could contribute to dissuade them from drilling for oil in Yasuni National Park. They asked for 3.6 billion dollars. However, they started drilling in 2013 when the trust fund only raised 13 million. But the Tosi Mpanu insisted the DRC weren’t bluffing and had a sovereign right to drill for oil.
Mpanu claimed oil companies could simply drill diagonally to avoid touching the peatlands. He assured everyone that they wouldn’t do anything without studying how it would affect the environment and the people in the area. But according to the New York Times, a Greenpeace team surveyed people who lived in the area. The people said they opposed the drilling and that they would protest it. He also argued that Congo had paid its climate dues by allowing the mining of minerals used in the renewable energy industry. He said, “We are part of the solution, but the solution also includes us making use of our oil resources.” He then admitted that the Congolese government would leave it up to the oil industry to decide if they wanted to drill in Virunga National Park. However, he also stated that the government could seek to protect other parcels of land to offset what they lost in Virunga. “If we lose 10 hectares, we could now protect 20,” he said. “Sure, it won’t have the same biodiversity and fauna, but the country has that right.” Asked what oil company would consider drilling in a protected gorilla habitat in an era where consumer awareness is higher than ever, Mr. Mpanu did not hesitate. He replied,

“It is what it is. We just have to see how much people value that resource.”

Dr. Simon Lewis made this point:

“It is unclear whether there really are substantial oil deposits beneath the Congo rainforest; if there is enough usable oil, it is also unclear whether getting it from such remote environments to global markets is economically viable. Yet, even if the initial survey revealed no commercial-scale oil deposits, the rainforests’ biodiversity value would still be destroyed. Once accessible and degraded, the rainforests would most likely succumb to rampant deforestation, increasing carbon emissions. In the peatlands, this disturbance would begin the release of carbon from the peat: up to 5.8 billion tons from the oil concession areas.”

Congo’s hydrocarbons minister said on their government’s website that they’ve consulted Angola, Nigeria, and Equatorial Guinea “so that the DRC can take the same path.”

We’ll continue to study the developments in this story, so stay tuned for the next exciting episode of The Gorilla Project podcast.


Climate change affects the relationship between chimps and gorillas in the wild

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Lara M. Southern of Osnabrück University in Germany went on the Gorilla Project podcast to discuss how climate change affected the relationship between chimpanzees and gorillas in the wild. She wrote the famous research paper entitled “Lethal coalitionary attacks of chimpanzees on gorillas in the wild.


“What you usually get with gorillas is you get a scent,” Lara described.


“They really smell very strong. Once you’re a chimp researcher, you can distinguish between this chimp and gorilla scent because it’s very different. We spend our whole days around chimps.”


Lara and the researchers initially thought there were levels of mutual avoidance between chimps and gorillas. Whenever they were in the forest, they could smell gorillas. They could see their feeding tracks and their footprints. So, they always knew they were there. They could also hear them sometimes. But Lara noticed that, to the chimpanzees, there was an indifference to the presence of gorillas. The scientists witnessed nine peaceful encounters between the two species. Lara even remembered seeing them eating figs together in a Ficus tree. Yet these friendly interactions didn’t surprise them because they were in line with research done at other field sites.


“So when these attacks happened,” Lara conceded. “It was something I don’t think I would have ever been expecting on any level.”


On the morning of February 6th, 2019, Lara and the researchers did what they always did- they got up very early to go to the nest site where their chimpanzees had slept the night before. At the nest site, they would begin their “focal follows,” following a different individual chimp each day.

“It’s the most exciting part about field research,” Lara thought. “Because you never know what’s going to happen.”


They set out to find the chimps (about five kilometers from the camp), and little did they know that they would walk thirty-five kilometers that day, one of the biggest “patrols” since the habituation study began.
To defend their territory, explore its boundaries, and ensure everything was in order, the chimpanzees would go on huge walks called “patrols.” They would be very silent, smell everything, listen intently, looking for neighboring communities. The researchers followed them to the very edge of their territory. At the very end of the day, dinner time, everyone was done and ready to go home.


“We were ready to put the chimps to bed and let them go nest,” Lara described.


It was around five o’clock when the forest was already getting dark.


“And that’s when all of the crazy commotions began.”


Listen to the full Gorilla Project podcast episode where Lara Southern tells the story in her own words.


Lethal attacks on gorillas by chimpanzees

Loango National Park in Gabon. The end of the day was when the chimps re-entered their territory after their patrol. Lara Southern and her team of researchers were following the day’s “focal”, an individual chimpanzee named Candy. They entered a dense part of the forest. After a while, they started to lose sight of the chimps. Then, they heard a distinctive scream of another chimpanzee named Freddy. It was immediately after that scream that they heard a bark. Lara’s head did a double take.


“Because they’re always screaming, but this bark really stuck out to me. And after that, it just exploded. A chimpanzee and a gorilla sound nothing alike. And then it was just this crazy cacophony of noise.”


The chimpanzees made alert calls, barks, and roars. The gorillas responded with roaring and barks of their own. The team didn’t have excellent visibility at first.


“We try and really keep our distance because they are completely wild animals, and we also have very high safety protocols,” Lara explained.


“There’s always these negotiations in the forest between when’s the time to leave versus your observation of what kind of data you’re going to get.”


The field guides were more interested in not getting their team injured. They tried to convince Lara that this situation was unsafe and that everyone needed to leave, but as a scientist, she felt they needed to stay and see what would happen. She repeatedly begged the field guides to let them observe for “just five more minutes… five more minutes”.


During this encounter, the chimps attacked a group of five gorillas: one silverback, one infant, and three females.


“This is unprecedented. I’ve never seen this before, I’ve never heard about this before,” Lara remembered thinking.

They tried to find a good vantage point to see what was happening. Lara and her team hid behind a massive log, peeping over the top. They made themselves known while staying far enough away to avoid interfering.


“I could describe it as kind of like a ball of chimps and gorillas, and we could see that the silverback was in the middle.”


Finally, the silverback charged the female adolescent chimpanzee named Gia (pronounced Gee-AH) and sent her flying into the air. Lara was worried when she saw the silverback attack the chimp.


“She was one of my favorite chimpanzees. She was always a big explorer,” Lara describes.

“She didn’t seem like a young female. She was really always with the males.”


The male chimps responded by surrounding the silverback and attacking him. He retreated with his family. The researchers later observed that the chimps captured the gorilla infant before the other gorillas could escape. The chimps passed the baby around for an hour and beat it to death. To this day, no one has found the body of the infant gorilla the chimps abducted.


Listen to the full Gorilla Project podcast episode where Lara Southern tells the story in her own words.


Lethal attacks on gorillas by chimpanzees

Even though Lara and the other scientists were entirely shocked by the first attack, she knew it was important to relay the information to their supervisors stationed in Germany. The most challenging part was to be thorough. Their write-up needed to capture every single detail in the exact way that it happened. Their thoroughness relied heavily on viewing their video footage over and over again.

“One thing I find very helpful is to watch animal behavior from behind the lens,” Lara suggested.

“So, when something crazy is happening or when something uncomfortable is happening, if you just film, there’s always this wall between you and what you’re seeing, and you can always remember your place as just an observer. That was something that helped me in both of those instances to document what I was seeing rather than put my own opinions on what I was seeing.”


On December 11th, 2019, Lara and her group of researchers followed the chimpanzee patrol far north of their home range territory.


“Whenever we go up there, everyone gets a little bit grumpy because there are the big swamps. And when there are swamps, it means you have to swim.”


Walking towards the northern swamps, they could see the chimps begin to change their behavior. Once they got outside their territory, they became reticent, displaying similar behavior to the lethal February 6th event. They walked in single file, sniffed the ground, and smelled the eaten fruit near a tree, searching for the presence of rival chimpanzee groups. The chimp named Freddy was in front, near a female named Joy. He stood up bipedal to get a better look at something, reacting to what he saw with alarm barks.


“My initial reaction (because I had already seen them on patrolling behavior) is that they had found a chimpanzee group,” Lara remembered.


The chimps found a family of seven gorillas feeding high up in the trees. They climbed up to attack them, forcing the silverback to retreat, leaving the mother gorillas defenseless. The silverback’s role was to protect his family, but Lara defended the silverback’s decision to flee.


“It was a pretty hard decision in that case. There were seven gorillas against a group of 27 chimpanzees. Chimpanzees are very loud, they’re very vocal, and they cooperate. This is something we talk about in the paper. They’re very cohesive in terms of behavior when they feel like their group is threatened or when they’re going into doing a collective behavior. All of them participate.”


And this occasion was no different. Every chimpanzee joined the attack- even the juveniles were barking at full-grown adult gorillas.


“Which is something that I haven’t really seen before. So, in a sense, the silverback fleeing, I think, was also just a choice of personal safety. I think it was a hard choice to make.”


Several other gorillas had already fled, so only two females and two babies were left in the group. Lara speculated that the silverback might have been attempting to initiate the movement of the remaining members of his family by trying to get them to follow him. The other two females were left high up in the canopy with their babies, allowing the chimps to climb up the tree and trap them. The chimpanzees chased one of the mother gorillas through the trees across the swamp, cornered her, and snatched her baby. Roxy, the older adult female chimp, ripped out the baby gorilla’s intestines and ate them, snacking on its body for hours.


“Roxy played everyone’s least favorite role in the second encounter because she’s the one who ingested the baby gorilla. So, she kept the prey, and she carried it with her, and she fed on it as a piece of prey for most of the afternoon after they caught the gorilla.”


Lethal attacks on gorillas by chimpanzees

The Conclusion: “Wait, but WHY?”

Chimpanzees were mostly frugivores. When they resorted to hunting, they ate things like insects, birds, lizards, and monkeys. No scientist could have imagined that a chimpanzee would ever hunt, kill or eat a gorilla. Lara M. Southern and her fellow researchers noticed these attacks were peculiar for many reasons. They shared characteristics of other chimpanzee hunts: they walked in single-file, made hunting calls, changed their direction silently, scanned the area, and other typical chimpanzee hunting maneuvers. Although it appeared that the chimps targeted the baby gorilla because it was smaller prey, this is where the similarities to other hunting tactics ended. She mentioned this in her research paper titled “Lethal coalitionary attacks of chimpanzees on gorillas in the wild“.

“That’s something we touch upon in the paper. We wanted to emphasize how different this was from hunting behaviors we’ve seen in the past and how much more similar this was to an inter-community encounter with other chimpanzees. They treated the gorillas as if they were neighboring groups intruding on their territory that they were at war with, which we’ve never seen them do with gorillas. It was very different from hunting, and we used the example in the paper where we talk about the noise levels.”

She explained that the chimps made lots of noise before they attacked, but the excitement instantly disappeared. They fell silent as soon as they captured the baby gorilla.

“And when you hunt, it’s completely the opposite,” Lara emphasized.


“There’s this very silent, coordinated hunting strategy, and feeding on the prey is the reward when they catch the prey.”

So here, the researchers saw that it was almost like the killing was the reward- much similar to inter-community encounters.

“There sometimes was cannibalism in inter-community attacks, but it was not so much as this baby as prey but as a symbol or collateral damage within a war.”

She also noticed that the incidents resembled previous attacks by chimpanzees against rival chimps in neighboring territories. For example, adults have killed infants from other communities to eliminate food competition by discouraging female chimps in the competing group from venturing into the disputed territory. However, this attack was the first time anyone witnessed chimpanzees doing the same thing to gorillas.

The researchers noticed that the event was unique due to how the chimpanzees ate the gorilla during the second attack. Chimp hunts typically involved the highest ranking male member possessing and eating the food first. They also tended to involve “food begging” by other lower ranking members and sharing based on rank. In this case, the researchers observed that a female ate the gorilla, only briefly sharing it with another low-ranking chimp. The high-ranking male chimp showed little to no interest in eating it.

How Climate Change Affected the Relationship between Chimpanzees and Gorillas in the Wild

The question remained: what caused the chimpanzees to suddenly view gorillas as rivals, attack them, and eat their baby? Lara Southern’s research cites Emma R. Bush’s paper titled “Long-term collapse in fruit availability threatens Central African forest megafauna.” The study used a rare long-term dataset of tree reproduction and a photographic database of forest elephants in Lopé National Park in Gabon. Did this long-term phenological data reveal the reason behind the high food competition between gorillas and chimpanzees? The paper-based its findings on one of the largest phenological databases in the world, indicating that the weather was getting hotter and dryer. The lowest average daily temperature in Lopé was increasing by approximately 0.25 degrees per decade.

“And that’s HUGE,” Lara stressed. “If you’re just thinking about in twenty years to come, we’re talking about a degree level of already extreme heat and extremely high temperatures for these species to cope with.”

The problem was that the trees in Lopé relied on the temperature to fall below a certain threshold to know when to begin flowering and producing fruit. Therefore, tree reproduction was cued less often due to the rising temperatures. The scientists discovered that trees in Lopé were producing fruit less often, and the probability of finding fruit was declining significantly over time. They witnessed a massive drop between 2000 and 2003. For example, September was the time for fruit scarcity in Lopé. It changed to between October and March, which was previously the historical time for fruit abundance. The average rate of finding fruit in trees went from approximately 1 in 10 in 1987 to 1 in 50 by 2018. In addition, it showed an 81% decline in fruiting between 1986 and 2018 and an 11% decline in the body mass of forest elephants from 2008 to 2018. The researchers witnessed that the decrease in fruit availability harmed the megafauna (specifically elephants, gorillas, and chimpanzees) residing in Lopé National Park.

“And I think you would see the exact same thing in Loango (National Park in Gabon) if we had that same comparable data set which hopefully we’ll be able to do soon.”

Lara explained in detail how these findings affected chimpanzees.

“They constantly know which fruit resources to go back and visit each year at a very specific time.”
Lara believed that this talent may not have been innate.


“It’s obvious that they learn, and it’s obvious that there are certain members of the group who teach others that there’s this rhythm and flow. We see this in all natural ecosystems. Nature has a problem and then a solution to everything. And it is things like climate change that really complicate these natural systems.”


“So chimpanzees, just imagine, for year after year, they’ve been going to these same sites, and all of a sudden, there’s these slight gradual changes that will have huge payoffs in their daily lives because it will affect their energy levels, their body mass, how far they’re able to travel, how tired they are, and how able they are to protect themselves against other groups. There are so many knockdown effects (that we couldn’t even quantify at this stage) that could be really harmful to not only these populations but populations everywhere.”

She went on to explain how this situation deteriorated the relationship between chimps and gorillas.

“So, chimpanzees and gorillas have a high dietary overlap,” Lara explained.


“They’re both great ape species, and they both share the same food types. Generally, we see on many other sites that there’s a level of niche partitioning. So, they’ve evolved over time to eat different species to limit these levels of competition. But what we think happens at Loango [National Park in Gabon] is that, at certain times of the year, where there are certain key [fruit] species that are favorite species of both gorillas and chimpanzees, you might get these levels of very high competition. And in this competitive atmosphere that’s already there, if you throw in a lower production season for all of those fruit species, you will get even higher levels of competition. So, we think that this might be happening, especially for certain years. This might be more pronounced. There’s a lot less ripe fruit available if it’s a bad fruiting season. And if this continually keeps happening, of course, sources of fruit become more clumped or even more dispersed and harder to find, and you’re attracting two great ape species to a limited resource. So, this creates a base for any form of conflict which you wouldn’t have if you had a larger abundance of fruits.”

There were countless researchers around the world collecting climate change information. Still, the data from the Emma R. Bush paper was a cumulative effort that took phenological data on such a precise level for decades. Then, finally, scientists began to see these critical patterns. Loango National Park researchers also had a phenology route to check the fruiting species. It was something that they monitored.

“But it’s so hard to know long-term seasonal trends in a normal variation because you really do need these long-term data sets. So what we did with the (Emma R.) Bush paper is we’ve taken a lot from that. Because I think there you can really see the drastic figures that they’re reporting: the number of things that are getting dryer, big problems with the rainy season. There are so many fruiting species that have those very specific requirements for temperature changes in order to fruit. Loango National Park, as well as Lopé, is a big stronghold for elephants, gorillas, and chimpanzees. So, it’s probably the exact same thing that’s happening. We just don’t have the data to support it. But we’re really working on getting there.”

Lara Southern and the researchers continued to study the encounters between gorillas and chimpanzees, their root causes, and piece together the data.

“We’re trying to fill in the gaps of what we couldn’t fill in in the first paper. This was really exciting research, and we wanted to get it out there and say, ‘Look! This is happening.’ There are so many angles to look at it from and why it’s interesting. It’s interesting from a species perspective just because we haven’t ever heard of this reported across any other field site where there are both chimpanzees and gorillas. They do coexist in other places, and this hasn’t happened yet. So, it seems that there must be something going on. And what you need is long-term data, so it’s an ongoing process. What I can say is that there do continue to be encounters.”


Listen to the full Gorilla Project podcast episode where Lara Southern tells the story in her own words.

Lethal attacks on gorillas by chimpanzees (part 4 of 4)


In part 3 of the story, Lara M. Southern described what it was like to witness both instances of lethal attacks on gorillas by chimpanzees. These events were unprecedented in the history of primatology, forcing scientists to study what was happening to cause it. Part 4 of our story asks: “why did the chimps do what they did?”


The Conclusion: “Wait, but WHY?”

Chimpanzees were mostly frugivores. When they resorted to hunting, they ate things like insects, birds, lizards, and monkeys. No scientist could have imagined that a chimpanzee would ever hunt, kill or eat a gorilla. Lara M. Southern and her fellow researchers noticed these attacks were peculiar for many reasons. They shared characteristics of other chimpanzee hunts: they walked in single-file, made hunting calls, changed their direction silently, scanned the area, and other typical chimpanzee hunting maneuvers. Although it appeared that the chimps targeted the baby gorilla because it was smaller prey, this is where the similarities to other hunting tactics ended. She mentioned this in her research paper titled “Lethal coalitionary attacks of chimpanzees on gorillas in the wild“.

“That’s something we touch upon in the paper. We wanted to emphasize how different this was from hunting behaviors we’ve seen in the past and how much more similar this was to an inter-community encounter with other chimpanzees. They treated the gorillas as if they were neighboring groups intruding on their territory that they were at war with, which we’ve never seen them do with gorillas. It was very different from hunting, and we used the example in the paper where we talk about the noise levels.”

She explained that the chimps made lots of noise before they attacked, but the excitement instantly disappeared. They fell silent as soon as they captured the baby gorilla.

“And when you hunt, it’s completely the opposite,” Lara emphasized.


“There’s this very silent, coordinated hunting strategy, and feeding on the prey is the reward when they catch the prey.”

So here, the researchers saw that it was almost like the killing was the reward- much similar to inter-community encounters.

“There sometimes was cannibalism in inter-community attacks, but it was not so much as this baby as prey but as a symbol or collateral damage within a war.”

She also noticed that the incidents resembled previous attacks by chimpanzees against rival chimps in neighboring territories. For example, adults have killed infants from other communities to eliminate food competition by discouraging female chimps in the competing group from venturing into the disputed territory. However, this attack was the first time anyone witnessed chimpanzees doing the same thing to gorillas.

The researchers noticed that the event was unique due to how the chimpanzees ate the gorilla during the second attack. Chimp hunts typically involved the highest ranking male member possessing and eating the food first. They also tended to involve “food begging” by other lower ranking members and sharing based on rank. In this case, the researchers observed that a female ate the gorilla, only briefly sharing it with another low-ranking chimp. The high-ranking male chimp showed little to no interest in eating it.

Did climate change cause the lethal attacks on gorillas by chimpanzees?

The question remained: what caused the chimpanzees to suddenly view gorillas as rivals, attack them, and eat their baby? Lara Southern’s research cites Emma R. Bush’s paper titled “Long-term collapse in fruit availability threatens Central African forest megafauna.” The study used a rare long-term dataset of tree reproduction and a photographic database of forest elephants in Lopé National Park in Gabon. Did this long-term phenological data reveal the reason behind the high food competition between gorillas and chimpanzees? The paper-based its findings on one of the largest phenological databases in the world, indicating that the weather was getting hotter and dryer. The lowest average daily temperature in Lopé was increasing by approximately 0.25 degrees per decade.

“And that’s HUGE,” Lara stressed. “If you’re just thinking about in twenty years to come, we’re talking about a degree level of already extreme heat and extremely high temperatures for these species to cope with.”

The problem was that the trees in Lopé relied on the temperature to fall below a certain threshold to know when to begin flowering and producing fruit. Therefore, tree reproduction was cued less often due to the rising temperatures. The scientists discovered that trees in Lopé were producing fruit less often, and the probability of finding fruit was declining significantly over time. They witnessed a massive drop between 2000 and 2003. For example, September was the time for fruit scarcity in Lopé. It changed to between October and March, which was previously the historical time for fruit abundance. The average rate of finding fruit in trees went from approximately 1 in 10 in 1987 to 1 in 50 by 2018. In addition, it showed an 81% decline in fruiting between 1986 and 2018 and an 11% decline in the body mass of forest elephants from 2008 to 2018. The researchers witnessed that the decrease in fruit availability harmed the megafauna (specifically elephants, gorillas, and chimpanzees) residing in Lopé National Park.

“And I think you would see the exact same thing in Loango (National Park in Gabon) if we had that same comparable data set which hopefully we’ll be able to do soon.”

Lara explained in detail how these findings affected chimpanzees.

“They constantly know which fruit resources to go back and visit each year at a very specific time.”
Lara believed that this talent may not have been innate.


“It’s obvious that they learn, and it’s obvious that there are certain members of the group who teach others that there’s this rhythm and flow. We see this in all natural ecosystems. Nature has a problem and then a solution to everything. And it is things like climate change that really complicate these natural systems.”


“So chimpanzees, just imagine, for year after year, they’ve been going to these same sites, and all of a sudden, there’s these slight gradual changes that will have huge payoffs in their daily lives because it will affect their energy levels, their body mass, how far they’re able to travel, how tired they are, and how able they are to protect themselves against other groups. There are so many knockdown effects (that we couldn’t even quantify at this stage) that could be really harmful to not only these populations but populations everywhere.”

She went on to explain how this situation deteriorated the relationship between chimps and gorillas.

“So, chimpanzees and gorillas have a high dietary overlap,” Lara explained.


“They’re both great ape species, and they both share the same food types. Generally, we see on many other sites that there’s a level of niche partitioning. So, they’ve evolved over time to eat different species to limit these levels of competition. But what we think happens at Loango [National Park in Gabon] is that, at certain times of the year, where there are certain key [fruit] species that are favorite species of both gorillas and chimpanzees, you might get these levels of very high competition. And in this competitive atmosphere that’s already there, if you throw in a lower production season for all of those fruit species, you will get even higher levels of competition. So, we think that this might be happening, especially for certain years. This might be more pronounced. There’s a lot less ripe fruit available if it’s a bad fruiting season. And if this continually keeps happening, of course, sources of fruit become more clumped or even more dispersed and harder to find, and you’re attracting two great ape species to a limited resource. So, this creates a base for any form of conflict which you wouldn’t have if you had a larger abundance of fruits.”

There were countless researchers around the world collecting climate change information. Still, the data from the Emma R. Bush paper was a cumulative effort that took phenological data on such a precise level for decades. Then, finally, scientists began to see these critical patterns. Loango National Park researchers also had a phenology route to check the fruiting species. It was something that they monitored.

“But it’s so hard to know long-term seasonal trends in a normal variation because you really do need these long-term data sets. So what we did with the (Emma R.) Bush paper is we’ve taken a lot from that. Because I think there you can really see the drastic figures that they’re reporting: the number of things that are getting dryer, big problems with the rainy season. There are so many fruiting species that have those very specific requirements for temperature changes in order to fruit. Loango National Park, as well as Lopé, is a big stronghold for elephants, gorillas, and chimpanzees. So, it’s probably the exact same thing that’s happening. We just don’t have the data to support it. But we’re really working on getting there.”

Lara Southern and the researchers continued to study the encounters between gorillas and chimpanzees, their root causes, and piece together the data.

“We’re trying to fill in the gaps of what we couldn’t fill in in the first paper. This was really exciting research, and we wanted to get it out there and say, ‘Look! This is happening.’ There are so many angles to look at it from and why it’s interesting. It’s interesting from a species perspective just because we haven’t ever heard of this reported across any other field site where there are both chimpanzees and gorillas. They do coexist in other places, and this hasn’t happened yet. So, it seems that there must be something going on. And what you need is long-term data, so it’s an ongoing process. What I can say is that there do continue to be encounters.”


Listen to the full Gorilla Project podcast episode where Lara Southern tells the story in her own words.