Earthquake on Chimp Mountain

It had been a long day in the field and we were all exhausted. I crawled into bed amid a thunderstorm and listened to the loud claps of thunder and the rushing sound of rain falling on the ground outside. I started to doze as the thunder gradually softened and the rain turned to light drizzle. Abruptly, I was jarred awake by the harsh and unmistakable vibrations of an earthquake. We ran outside and waited another 30 seconds or so until it passed. Everything seemed fine. No major damage, but people yelled loudly from the nearby village as monkeys gave loud alarm calls. This earthquake was the second in as many days. The first measured magnitude 5.2. This one felt quite a bit stronger, measuring magnitude 5.7. We had a restless night, with aftershocks as strong as magnitude 5.4 occurring frequently throughout the night. Seismic activity is not uncommon in this area. Western Uganda lies along the Albertine Rift, an active area of tectonic shifts that are slowly separating the Somali Plate in East Africa from the rest of the continent. The earthquakes we’ve experienced in the past week have had their epicenter along the rift in Lake Albert to the west.On our way to the field the next morning, we were all a bit bleary-eyed, but the earthquake was an animated topic of conversation among all. Amid our discussions of how our Ugandan friends responded to the event, I wondered how the chimpanzees in the region fared as well. Ethologists and others have written numerous articles regarding how animal behavior changes preceding and during seismic activity (e.g., Buskirk et al. 1981; Shaw 1977). Most of these accounts have come from captive animals. For example, in 2011 the National Zoo described the responses of various animals to an earthquake of magnitude 5.8 in the Washington, DC area. Orangutans and western lowland gorillas were among the zoo inhabitants to respond to the quake, with members of both species climbing higher in their enclosures and vocalizing.
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What about free-living primates? Snarr (2005) similarly reported that wild mantled howler monkeys (Alouatta palliata) responded to an earthquake by vocalizing and climbing higher in the trees. Fujimoto and Hanamura (2008) provided a rare account of wild chimpanzee responses during a strong earthquake and its aftershocks in the Mahale Mountains, Tanzania. The chimpanzees vocalized loudly (but were not visually observed) during the main quake. During aftershocks, they typically responded by climbing higher or by interrupting their activities. Interestingly, one female was observed to climb down and touch the ground with her hand, as though to explore the vibrations she was feeling from the ground. Few other accounts exist regarding the behavior of wild non-human primates in response to earthquakes, however.
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When we arrived in the field, we met with two farmers who gave us their own account of the previous night’s events. They were tending an evening fire at their small hut at the garden’s edge.  The garden is situated on a steep hillside in a mountainous rural area. There is a small forest patch near the garden, and the farmers knew chimpanzees were nesting there. When they began to feel the tremors, they also heard the screams of chimpanzees. The vocalizations quickly grew nearer, and soon they saw an estimated 20 chimpanzees in the garden outside their hut. Amid their surprise, they grew concerned that the chimpanzees had run out of the forest to attack them in response to the quake. They banged their machetes on rocks to intimidate the chimps, who went running back into the forest.
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When the farmers awoke in the early morning hours, the chimpanzees called from another patch of forest about 300 meters away. The men were surprised that the chimpanzees seemed to have moved their nests in the middle of the night. Perhaps this shift was related to the strong aftershocks during the night.
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Because we weren’t there, we have no way of confirming whether their account of events is entirely true. However, everything else they told us—the locations of nests, what the chimps had been feeding on, and where they went in the morning—was borne out by the evidence we later found. In short, I have no reason to suspect that their account is anything other than accurate.
What can we make of this account? If chimpanzees did climb down from the trees and leave the forest as the farmers said, this would contrast sharply with Fujimoto and Hanamura’s account of chimpanzee responses to seismic activity.  Indeed, most accounts of responses by captive and free-living primates indicate that climbing up is a more likely response. Perhaps, though, there are reasons why climbing down would be more sensible for these chimpanzees. First, their remaining forest is small and degraded, and surviving nesting trees may be much smaller than those seen elsewhere. Smaller trees may move more and provide less stability during seismic events, making them a less secure option than the ground. The frequent felling of trees in this area may also make chimpanzees particularly wary of the possibility of a tree falling during seemingly dangerous situations. In addition, there are no large carnivores like leopards here, as have been reported the Mahale Mountains, so perhaps moving to the ground at night is perceived as less dangerous. Unfortunately, the paucity of observations of such events makes it difficult to observe these responses and clarify their meanings. Nonetheless, it is fascinating to consider how chimpanzees, humans, and our ancestors may have responded to seismic activity over the course of evolutionary history.
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Buskirk, R., Frohlich, C., Latham, G. (1981). Unusual animal behavior before earthquakes: a review of possible sensory mechanisms. Rev Geophys Space Phys, 19, 247 – 270.

Fujimoto, M., Hanamura, S. (2008). Responses of wild chimpanzees (Pan troglodytes schweinfurthii) toward seismic aftershocks in the Mahale Mountains National Park, Tanzania. Primates, 49, 73 – 76.

Shaw, E. (1977). Can animals anticipate earthquakes? Nat Hist, 83, 14 – 20.

Snarr, K. (2005). Seismic activity response as observed in mantled howlers (Aloutta palliata), Cuero y Salado Wildlife Refuge, Honduras. Primates, 46, 281 – 285.

 This post was originally published at Scientific American


Hunting for Answers

We recently embarked on data collection in a new community of chimpanzees. They were new to us, that is, though we had heard a great deal about them. We heard from local friends that this is a large community, consisting of more chimpanzees than other communities nearby. We heard that they come into conflict with embittered human neighbors more often than anywhere else we have been. We also heard that these chimpanzees are “very tough,” killing goats with fierce slaps, surrounding and killing an antelope, and beating a python to death by hitting it against a tree. They were a fearsome group, as the stories went.

While heading to the forest on our first day of data collection there, I couldn’t help but wonder what we would find. Though the tales loomed large, I expected these chimpanzees to be more or less like the others we’ve observed. After all, they live only a few miles from neighboring communities, and by now, we feel like seasoned visitors to chimpanzees in the region. It’s as though we are houseguests who crash on the sofa for a few days, getting a glimpse into the lives of our hosts before moving on to the next place, never overstaying our welcome too long. After so many miles traveled, so many glimpses into chimpanzee lives, we are not easily surprised.

Our first few days of data collection were productive but not extraordinary. The chimpanzees were gathered in a large party, making them relatively simple to locate. We collected many dung samples easily. After a few days, Emily, a volunteer for my project, asked for some help while washing a dung sample for diet analysis. What, she asked, was the strange-looking stuff in this sample? Upon closer inspection, I realized what we were scrutinizing: the hand of a black-and-white colobus monkey (Colobus guereza). The delicate skin, hand bones, fingernails, and hair were all visible. The evidence was gruesome but clear: The chimpanzee who produced the sample had eaten part of a colobus monkey.

For chimpanzees across studied sites in Africa, animal protein—including meat, insects, and eggs—comprises a small proportion of the diet, typically around 8 – 10% overall (Goodall 1986).  Red colobus monkeys (Procolobus spp.) are the favored prey animal for chimpanzees where the two species overlap. In our study region, there are no red colobus monkeys. Instead, chimpanzees consume black-and-white colobus monkeys among several other species in the nearby Budongo Forest (Newton-Fisher et al. 2002; Reynolds 2005). Black-and-white colobus hunting has also been reported at the Kasokwa Forest, a forest fragment just to the south of the Budongo Forest (Reynolds 2005). As research volunteers in 2007, Jack and I even observed chimpanzees hunting and eating a black-and-white colobus monkey in Kasokwa.

Despite known instances of hunting at Kasokwa, however, little evidence to date has shown extensive hunting by other chimpanzees in this fragmented forest region. Although my colleague Matt McLennan has analyzed the dietary components of over 2,000 chimpanzee dung samples at nearby Bulindi, he has never found evidence of colobus consumption (pers. comm.). My analyses so far have similarly yielded a dearth of animal protein in the diet.

Now, however, we had our first clear evidence of meat consumption. The next day, we watched as a party of chimpanzees fed in a Pseudospondias microcarpa tree, a common tree that produces fruits enjoyed by chimpanzees among other species. After the chimpanzees left, we searched for dung samples beneath the tree. As we looked, Nick told us he had just seen a female chimpanzee in a nearby Psuedospondias tree. We took a closer look and found the lone female sitting calmly and eating a young black-and-white colobus monkey. We watched in utter fascination for thirty minutes or more as she slowly consumed the carcass, taking intermittent bites of leaves between bits of meat. This “steak with salad” style of meat consumption is a commonly observed dining practice among chimpanzees, and may aid in the processing of raw meat. As we watched her eat, we wondered how she came to have this prized catch. Hunting is usually a group activity and a male-dominated affair among chimpanzees (Stanford et al. 1994). High-ranking males often come away with the best chunks of meat, which they may share with persistent community members who pester them until they give in and share their spoils.

How did this lone female end up with an entire monkey, then? Did she take advantage of an opportunity to snatch a young monkey on her own? If so, were the other members of her party still nearby in the neighboring Pseudospondias tree when she went in for the kill, or did she stay behind after the others left to opportunistically hunt? Alternatively, did another hunter share the meat with her?

The next day, we observed yet another instance of hunting. It was morning, and we had just arrived to hear choruses of excited vocalizations along with the throaty calls of black-and-white colobus monkeys. We strained to watch from a distance as they leapt between trees. Nick had the perfect view to see the culmination of their efforts. Three adult chimpanzees surrounded a colobus. One chimpanzee stayed low in the tree while the other two cornered it from above. Then, one of them reached out and grabbed the monkey. We observed as they divided their prey and proceeded to feast on it.

We now had evidence of three hunting instances in one week. This series of events left us with us with more questions than answers. Did we catch this community during a particularly active period of hunting? Hunting rates in chimpanzees are known to fluctuate based on a variety of factors including party size, food availability, and the presence of estrus females (e.g., Gilby and Wrangham 2007; Mitani and Watts 2001; Stanford et al. 1994).  Another question, not mutually exclusive, is whether these chimpanzees are simply more apt to hunt than other nearby communities. Does something about the community composition (e.g., the presence of numerous males) favor a “culture of hunting”? Did the environment somehow promote more hunting opportunities? For example, might the density of black-and-white colobus monkeys be particularly high in this forest fragment, leading to more hunting opportunities? For now, answers elude us. Instead, the questions propel us forward in anticipation of what the next field day might bring among these “very tough” chimpanzees.


Gilby, I. C., Wrangham, R. W. (2007). Risk-prone hunting by chimpanzees (Pan troglodytes schweinfurthii) increases during periods of high diet quality. Behavioral Ecology and Sociobiology, 61, 1771 – 1779.

Goodall, J. (1986). The chimpanzees of Gombe: patterns of behaviour. Cambridge, MA: Harvard University Press.

Mitani, J. C., Watts, D. P. (2001). Why do chimpanzees hunt and share meat? Animal Behaviour, 61, 915 – 924.

Newton-Fisher, N. E., Notman, H., Reynolds, V. (2002.) Hunting of mammalian prey by Budongo Forest chimpanzees. Folia Primatologica 73, 281 – 283.

Reynolds, V. (2005). The chimpanzees of the Budongo Forest: ecology, behaviour, and conservation. New York: Oxford University Press.

Stanford, C. B., Wallis, J., Mpongo, E., Goodall, J. (1994). Hunting decisions in wild chimpanzees. Behaviour, 131, 1 – 18.

This post was originally published at Scientific American




Their chorus of pant hoots gave them away in dramatic fashion. The chimpanzees we’d been looking for were nearby, and we knew exactly where to find them. Though farmland and trees blocked our view, we could hear that the chimpanzees had arrived at a particular fig tree laden with ripe fruits. As ripe fruit specialists, chimpanzees seek out fruiting figs like this Ficus exasperata. On a good day, we can use our knowledge of when these figs are ripening to help us find the chimpanzees.

We took a circuitous route through the gardens to a grassy hilltop with a clear, albeit distant, view of the Ficus.  I dropped my backpack and pulled out my binoculars. I began to scan the tree in an attempt to identify the large dark figures foraging. I could make out the silhouettes of at least seven or eight chimpanzees, all foraging on figs or seated in the huge tree.

Chimpanzees feed in a Ficus exasperata tree. Photo: Jack Lester.


After observing their foraging for a few peaceful moments, I heard a jarring but familiar sound. A man working in a garden nearby shouted at the chimpanzees. Though the tree was in an isolated area of grassland several dozen meters from where he worked, he was clearly uncomfortable with their presence. A few threatening shouts were enough to convince the chimpanzees it was best to cut short their breakfast. They descended quickly from the fig. I now counted twelve chimpanzees as they walked in a single file line back across the grassland and to a small patch of forest nearby. As we watched them go, field assistant Nick commented that he felt sorry for the chimps. At times like these, I am reminded of one of the most recurrent lessons from my research thus far: chimpanzees are surprisingly resilient. They may have waited until later to forage, or perhaps they found another source of nutrition (which, unfortunately, may have involved risky crop-raiding). However, as long as no one hunted them or set a mantrap to ensnare them, as is sometimes the case, they probably found something to eat and survived another day. Despite the rapid rate of forest degradation in their habitat, they have persisted. They continue to forage, reproduce, and tend to the complex political matters of chimpanzee life, even if these behaviors must be modified somewhat to fit a drastically altered environment.

I was again reminded of chimpanzee resilience when, on a recent visit to my mother’s home, I opened an old box to find my childhood collection of troll dolls. After a moment’s consideration, I decided to send them to a chimpanzee named Foxie. Foxie is a resident of Chimpanzee Sanctuary Northwest (CSNW), a sanctuary in Cle Elum, Washington that serves as home to seven chimpanzees. The “Cle Elum Seven,” as they are known, have lived in biomedical laboratories for most of their lives. They were involved in invasive hepatitis vaccine research and used for laboratory breeding. Foxie gave birth to five infants, but was forced to give them all up, just like so many other breeding female chimpanzees in laboratories. Perhaps as a fulfillment of the maternal behaviors she was never able to express, Foxie can now usually be found carrying a troll or other doll with her.

Foxie cares for a troll doll. Photo courtesy Chimpanzee Sanctuary Northwest, used with permission.

Foxie cares for a troll doll. Photo courtesy Chimpanzee Sanctuary Northwest, used with permission.









The caregivers who know Foxie and the other members of the Cle Elum Seven can attest to this adaptability. All seven have displayed drastic changes in both behavior and physical appearance since arriving at CSNW several years ago. The shift from a windowless laboratory basement to a spacious sanctuary with dedicated caregivers and outdoor access has—not surprisingly—had an unambiguously positive effect on them.

Why might chimpanzees be so adaptable to change?  It may have aided the survival of their ancestors–and ours. For example, many primates regularly face drastic seasonal changes in rainfall, temperature, and food availability. Some primates have specialized adaptations that help them survive under harshly changing seasonal conditions. For chimpanzees, a learned knowledge of the fruit tree locations, even during periods of low fruit availability, is critical. Chimpanzees acquire this knowledge over a prolonged period of development, with high reliance on their mothers until full weaning at age 5, followed by juvenile and sub-adulthood learning periods lasting until age 15. A high degree of neural plasticity facilitates this learning ability. In humans, an especially high degree of plasticity may aid our strong reliance on learning. Plasticity may also play a key role in what we call resilience, enabling both humans and our chimpanzee kin to roll with the punches during trying times. For chimpanzees today, this may mean finding a new fruit tree when one due to ripen has been felled, or basking in the sun for the first time after decades inside a laboratory.

This post was originally published at Scientific American.