Category Archives: Gombe

Chimpanzees, Gombe, Language and communication

Do Chimpanzees Have Dialects?

September 30, 2022 DaktaMaik

I grew up speaking English, first in Minnesota, then in central Illinois. On visits back to Minnesota, friends teased me for having a “southern” accent, like when I described a gar fish as looking “right like an alligator.” I encountered other varieties of English when we moved to Indiana — twangier than the downstate Illinois drawl — and when I went to college in Chicago. But these varieties of American English paled in comparison to what I encountered in Britain, when I spent a year as an exchange student at Cambridge University. As a fan of British television shows (Monty Python, Doctor Who, David Attenborough) and music (the Beatles, Pink Floyd), I expected to understand what people were saying. It turned out to be much trickier than I expected. Instead of the Received Pronunciation of BBC broadcasts, I encountered rapid speech with unfamiliar slang (“naff,” “grotty,” “phoar!”), new vocabulary words (“bog,” “crisps,” “snog”), expressions (“over the top,” “get off with,” “taking the mickey”), with consonants often ghosted as glottal stops. And there wasn’t just one variety to learn. People from different cities, regions, islands and social classes all spoke differently. Chris from Birmingham (“Brum”) spoke in a rapid series of unintelligible words and knowing looks that often left me completely baffled.

Different varieties of languages – dialects – likely emerge as an inevitable consequence of cultural evolution. People learn their home language from their parents, but they don’t learn it exactly the same. They add new words and phrases and ways of speaking that they pick up from their friends, and in the modern world, other sources like books, television, and the internet. As these differences accumulate, ways of speaking diverge. Descent with modification leads to the formation of new languages, just as in biology it produces new species.

Do other animals have dialects? Peter Marler, a pioneer in the study of animal behavior, demonstrated that some animals do. Songbirds have two main categories of calls: short, simple calls for everyday use, such as predator alarm calls, and more elaborate songs, mostly used during the mating season. Birds sing to defend territory, attract mates, and once mated, to communicate with their partner. Over the course of a long career, Marler conducted an elegant series of field studies and laboratory experiments, demonstrating that in species such as white-crowned sparrows, songs must be learned. A sparrow raised in isolation produces abnormal songs, but if he hears recordings of songs while growing up, he produces a normal song. Because sparrows learn their songs, local variants emerge and gradually change over time, producing regional dialects (Marler, 1970). (Here’s a video describing recent work on dialects in white-throated sparrows.)

Subsequent studies found evidence of such ability to modify calls — vocal learning — in some other species. Humpback whales, for example, sing long, complicated, haunting songs during their mating season. Like in sparrows, males do most of the singing. Whale songs vary not just by region, but also by year. In a given year in Hawaiian waters, male humpbacks sing songs that closely resemble one another, but which differ from what the whales are singing off the coast of Australia — and which also differ from last year’s favorite styles in Hawaii (Mercado et al., 2004).

Do species more closely related to humans, such as chimpanzees, show any evidence of vocal learning and dialects?

Marler pioneered the study of primate communication as well as birdsong. He visited Gombe National Park, Tanzania, in 1967, where he carried out the first modern field study of chimpanzee vocal communication. Based on his recordings from Gombe, Marler identified a set of 13 basic calls for chimpanzees. He also found that chimpanzee calls generally resembled those of gorillas (Marler, 1976). The similarity of calls among these apes suggests they are mainly under genetic control, rather than learned. However, John Mitani, working as a post-doctoral researcher with Marler, found some evidence for dialects in chimpanzee pant-hoot calls (Mitani et al., 1992).

When Jane Goodall gives public talks, she often begins by giving a pant-hoot: a loud call that begins with soft hoos, followed by grunts, barks or screams, and often ends with grunts again. (Jane usually leaves out the screams, though, as she thinks those sound too aggressive.)

Spectrogram of chimpanzee pant-hoot call, from Desai et al. (2022)

Pant-hoots are loud, and enable chimpanzees to communicate over long distances through the forest. Mitani recorded pant-hoots from chimpanzees at Mahale Mountains, some 160 km south of Gombe, and compared them to Marler’s recordings of pant-hoots from Gombe. Analysis revealed some subtle differences: Mahale chimpanzees produced shorter grunts at a faster rate than Gombe chimpanzees, and produced pant-hoots with higher-pitched screams (Mitani et al., 1992). Later studies reported similar geographic variation in calls among groups of captive chimpanzees (Marshall et al., 1999), between chimpanzees in Uganda and Tanzania (Arcadi et al., 1996), and among communities of chimpanzees at Taï Forest in Côte d’Ivoire (Crockford et al., 2004).

The idea that chimpanzees have distinct pant-hoot calls is an intriguing one. Moreover, the study led by Cathy Crockford (2004) reported that neighboring communities differed from one another more than they did from more distant communities. This suggested that chimpanzees produced calls that announced their community membership to other chimpanzees. This would make sense, given the hostile relations between chimp communities. A pant-hoot call would function like a sports team uniform or national flag, announcing the caller as a member of team Mitumba or Kasekela. Perhaps vocal learning evolved in our own ancestors in response to selection pressure from intergroup aggression?

As a graduate student, I conducted a series of playback experiments with chimpanzees in Kibale National Park, Uganda (Wilson et al., 2001). I used recordings that Mitani had made of chimpanzees from Mahale. In each experiment, I played back a single pant-hoot from a Mahale chimp from a speaker hidden hundreds of meters from Kibale chimpanzees. This single simulated intruder provoked an immediate and striking response. If the listening party consisted only of females, they silently climbed down from the tree where they had been resting or feeding and moved off in the opposite direction. If one or two males heard the call, they stayed silent, and either stayed in place, looking towards the source of the call, or slowly approached the speaker. If three or more males heard the call, though, they immediately gave a loud vocal response and rapidly approached the speaker, as if they were looking for an intruder to attack. So chimpanzees can clearly tell friend from foe by their voice. But were they responding to differences in dialect? Or just differences in familiar versus unfamiliar individuals?

As Mitani and his team continued to analyze calls from different chimpanzee sites, though, they dialed back on claims of dialects. When Mitani began recording calls at Kibale, he found that chimpanzees in Kibale do produce pant-hoots with build-up elements, despite the previous report that they don’t (Mitani et al., 1999). They also found that much of the variation in acoustic structure occurred within individuals, rather than between communities.

So, do chimpanzees have dialects or not? In an effort to answer this question, I worked with my graduate student, Nisarg Desai, and a team of Tanzanian field assistants to record and analyze chimpanzee vocalizations. Team members followed chimpanzees through the forest, carrying a hand-held “shotgun” microphone and a digital recorder, recording as many calls from each individual as possible.

Three researchers at Gombe National Park, Tanzania — The Chimpanzee Dialects Project team at Gombe: Nasibu Madubmi, Hashimu Salala, and Nisarg Desai.

When Nisarg analyzed the data, he found that individuals varied a lot in the calls, but community membership explained little of the variation between the calls. Analyzing calls that Pawel Fedurek had recorded in Kibale, Nisarg again found lots of variation among individuals, but no clear geographical variation (Desai et al., 2022).

Acoustic analyses from Desai et al (2022). Pant-hoots from the different communities showed lots of overlap in their acoustic features.

Based on Nisarg’s findings, and on the subtle differences reported from other studies, I’m inclined to think that chimpanzees do not have dialects after all. Chimpanzees and other apes may yet prove to have some limited capacity for vocal learning. But any such capacities in nonhuman apes pale in comparison, not just to humans, but also to many birds and whales in terms of vocal learning. This aspect of language seems to have emerged only after our ancestors diverged from the Pan-human ancestor.

Figure showing results from acoustic analysis of chimpanzee pant-hoot calls. — Most of the variation in acoustic features occurred among individuals within communities, rather than between communities. (Desai et al., 2022)

All of this raises questions about what promotes vocal learning in other species, and whether similar factors promoted vocal learning in human ancestors. To be continued!

Researcher with chimpanzees — Nisarg Desai with chimpanzees Sandi, Ferdinand, and Siri at Gombe National Park, Tanzania

References

Arcadi, A. C. (1996). Phrase structure of wild chimpanzee pant hoots: patterns of production and interpopulation variability. American Journal of Primatology, 39(3), 159-178.

Crockford, C., Herbinger, I., Vigilant, L., & Boesch, C. (2004). Wild chimpanzees produce group‐specific calls: a case for vocal learning?. Ethology, 110(3), 221-243.

Desai, N. P., Fedurek, P., Slocombe, K. E., & Wilson, M. L. (2022). Chimpanzee pant‐hoots encode individual information more reliably than group differences. American Journal of Primatology, e23430.

Marler, P. (1970). Birdsong and speech development: Could there be parallels? There may be basic rules governing vocal learning to which many species conform, including man. American scientist, 58(6), 669-673.

Marler, P. (1976). Social organization, communication and graded signals: the chimpanzee and the. Growing Points Ethology, 239.

Marshall, A. J., Wrangham, R. W., & Arcadi, A. C. (1999). Does learning affect the structure of vocalizations in chimpanzees?. Animal behaviour, 58(4), 825-830.

Mercado, E., Herman, L.M. & Pack, A.A. Song copying by humpback whales: themes and variations. Anim Cogn 8, 93–102 (2005). https://doi.org/10.1007/s10071-004-0238-7

Mitani, J. C., Hasegawa, T., Gros‐Louis, J., Marler, P., & Byrne, R. (1992). Dialects in wild chimpanzees?. American Journal of Primatology, 27(4), 233-243.

Mitani, J. C., Hunley, K. L., & Murdoch, M. E. (1999). Geographic variation in the calls of wild chimpanzees: a reassessment. American Journal of Primatology: Official Journal of the American Society of Primatologists, 47(2), 133-151.

Wilson, M. L., Hauser, M. D., Wrangham, R. W. 2001. Does participation in intergroup conflict depend on numerical assessment, range location, or rank for wild chimpanzees? Animal Behaviour 61(6): 1203-1216. https://doi.org/10.1006/anbe.2000.1706

Gombe, Tool Use

Twins and Cousins

July 22, 2014 DaktaMaik

Gombe is a special site for many reasons. Among them: It is the first site where wild chimpanzees were observed to make and use tools. It is also the only wild site where twin chimpanzees have survived to adulthood. On my recent visit to Gombe, I had the good fortune to see the twins and their daughters making and using tools to fish for termites.

Back in 2002, I remember following a large group of chimps in the Kasekela community, on the narrow trail climbing the steep path above Kakombe Valley, heading south to Mkenke Valley. It was Mabungo season and the chimps were feasting on fruits from the different kinds of Mabungo vines, especially Mabungo Makubwa (Big Mabungo) and Mabungo Madogo (Little Mabungo). The chimps traveled single file down the narrow trail. In the midst of the rainy season, everything was lush, green, and wet. The last chimp in the line was Gremlin, carrying her twins, Golden and Glitter, on her back. Sometimes their older sister Gaia would help mom by carrying one of the little twins. Gaia’s help is probably one reason that Golden and Glitter survived to adulthood — the only known pair of wild chimp twins known to have done so. Even with this help, though, the twins slowed Gremlin down. Being new to Gombe, struggling with the hikes up and down the hills, I was quite happy walking behind them, grateful for a chance to rest a little while watching these little girls play.

Amri collecting data on the twins, Gitter and Golden, and their babies, Gossamer and Glamour.

Now Golden and Glitter are all grown up. Female chimpanzees usually leave the group of their birth and join a new one, to avoid mating with their brothers, uncles, fathers and such. At Gombe, though, about half of the Kasekela females stay in their natal group, probably because the dispersal options are limited: Mitumba is small and crowded, while Kalande is big but less forested (so less food) and has too few adult males. So Golden and Glitter have stayed in Kasekela, as did their mother Gremlin.

We don’t know if Gremlin’s mother Melissa was born in Kasekela or if she immigrated from elsewhere. But now that Golden and Glitter have babies of their own (Glamour and Gossamer), we have four generations of G-family girls in one community. Their older sister Gaia has also stayed in Kasekela. When all the G-family moms and babies get together, it’s more like a baboon matriline than a typical chimpanzee group of unrelated females. This concentration of female kin might have some interesting implications for social behavior. Maybe all these related females will gang up on other females to control access to the best home ranges? They do seem very well established in Kakombe Valley, the best, most productive valley in Gombe in terms of chimpanzee foods.

Glamour, who just like her mother Golden, has a white spot on the top of her head. (11 June 2014)

This June, in between visits to the Kalande and Mitumba communities, I was able to spend some time following the twins and their daughters.

They spent much of the morning fishing for termites. Usually there’s more termite fishing in the wet season than this time of year, the early dry season, but perhaps the recent rains had softened up the mounds enough to make it easier for the chimps to stick in their termite fishing tools: wands made of grass or sticks, stripped of leaves to make slender probes.

Golden eating termites from her fishing wand.

Golden standing quadrupedally and holding her wand in her mouth. (11 June 2014) — Golden standing quadrupedally and holding her wand in her mouth.
(11 June 2014)

Jane Goodall’s discovery that chimpanzees make and use tools to fish for termites was one of the key findings that made Jane and Gombe famous. In The Descent of Man, Darwin argued that the making and using of tools originated after the evolution of bipedalism: walking on two legs freed the hands for manipulation, rather than transportation. It was therefore a surprising discovery that these knuckle-walking forest apes regularly used their hands, not just for walking and climbing, but also for making and using what has turned out to be a large variety of tools.

Tools increase access to important foods that would not otherwisebe available. Termites, for example, are rich in fat and protein, nutrients that are important but not well supplied by the mainstay of chimpanzee diet, ripe fruit.

Golden eating termites from her hand. (11 June 2014) — Golden eating termites from her hand.
(11 June 2014)

Tool use also increases the value of social learning. Termite fishing is a skill that takes years to learn properly, and kids mainly learn how to termite fish from watching their moms. As Elizabeth Lonsdorf elegantly showed with her studies of termite fishing at Gombe (in which Gremlin and the twins figured prominently), girls learn to termite fish faster than boys, probably because boys are too busy playing rough-and-tumble games.

Once cultural learning is established, a whole range of new subsistence strategies can be acquired that any one individual would never think to invent on their own.

Darwin was probably right that being bipedal helps with making and using tools. Chimpanzee hands are long, with curved fingers and short, weak thumbs. Australopith hands are much better suited for both the precision grip and the power grip. They must have had a much broader range of tools than chimpanzees: sticks for digging food and hitting rivals, stones for smashing food and throwing at enemies. But the discovery of tool use and material culture in chimpanzees suggests that these practices may have already been present in our common ancestor with chimpanzees, predating the origin of bipedalism — and perhaps providing increased selective advantages for individuals in those populations that first started standing bipedally a bit more than usual.

Imani standing bipedal to feed. (10 June 2014) — Imani standing bipedal to feed.
(10 June 2014)

Gombe, Intergroup Conflict

Mitumba

July 10, 2014 DaktaMaik

On Thursday, 12 June, Deus, Rebecca and I visited the Mitumba community in the North of Gombe.

Gombe is one of the few sites where researchers can study neighboring chimpanzee communities. At most sites, researchers focus on a single study community, and don’t know very much about the neighbors. This was the case at Gombe for many years, but since the Mitumba chimpanzees were habitatuated in the 1990s, we have been able to follow chimpanzees from two communities simultaneously. And now, with monitoring of the Kalande chimpanzees, we can track the movements of nearly every chimpanzee in the park.

The prospect of studying intergroup interactions from both sides of the event is what led me to start working at Gombe, and has been a focus of my research ever since. Deus has played a big part in this, as he collected data on the Mitumba chimpanzees, first as a research assistant on the intergroup relations project, and then as a PhD student.

When I first started working at Gombe, we worried that males from the larger, more powerful Kasekela community would kill the remaining males from Mitumba and take over their range. And sure enough, soon after I started working at Gombe, the young male Rusambo was found dead, with severe wounds, the day after Kasekela males traveled deep into Mitumba’s range (Wilson et al., 2004).

However, since then, the Mitumba males have held on, and even seem to have expanded their range a bit. And while intergroup incursions from Kasekela have continued, including the killing of the young infant Andromeda (Wilson, 2013), it is the Mitumba males who have proved a greater threat to themselves. Mitumba males Edgar and Rudi killed their former alpha male, Vincent, in 2004. Soon after, the young male Ebony was found dead. Since then, Edgar and Rudi have fought bitterly and Rudi has disappeared. Edgar seems determined to keep Mitumba for himself, as if he were a gorilla silverback.

When we arrived in Mitumba, we walked up the steep, narrow valley of Mitumba stream. Gnarled old Mgwiza trees grow along the stream banks, and Lusieno trees tower overhead.

Flirt climbing down from her feeding tree.

We found chimps close to the stream. Edgar followed Flirt closely. She had a full swelling and he clearly wanted to keep her all to himself. Flirt is one of Fifi’s daughters. She was born and raised in Kasekela. She was orphaned when her mother died in 2004, but managed to survive, spending much of her time with older brother Frodo. Flirt is one of the very few chimpanzees I ever saw Frodo groom.

After Flirt reached sexual maturity, she did what female chimpanzees usually do: transferred to a new community. With Edgar showing so much interest in her, maybe she will conceive an infant soon.

Young male Apple followed them from a distance. Apple is one of the rising generation of Mitumba males, along with Kocha and Ramba. If these boys survive to maturity, then Mitumba may have a chance at keeping Kasekela at bay and maintaining Mitumba as a viable community. But with Edgar’s track record of attacking other males, maybe he won’t let these young competitors survive. If Edgar continues killing all the young males, his line may end in a Pyrrhic victory: eliminating not only his competitors, but his only allies against the mighty Kasekelans.

After coming down from the trees, the Mitumba chimpanzees soon climbed up the steep slide of the hill, giving us a chance to experience some classic Mitumba chimp viewing: crawling on hands and knees through vine tangle.

Conservation, Gombe, Health, Intergroup Conflict, Isotopes

Kalande

June 26, 2014 DaktaMaik

On June 10th, I traveled to the south of Gombe to visit the range of the little-known Kalande community of chimpanzees.

Map of Gombe National Park and chimpanzee ranges (from Rudicell et al., 2010)

The Kalande community is one of three chimpanzee communities at Gombe.

The most famous, most intensively studied chimpanzees live in the Kasekela community in the center of the park. These are the chimpanzees that Jane Goodall has studied since 1960. They have the biggest range and the most members of the park’s three communities.

To the north of Kasekela live the Mitumba chimpanzees. This is a smaller community, which Deus Mjungu studied for his PhD research. The Mitumba community has fewer chimpanzees than Kasekela, but is still vigorous. They have a small range, but it includes excellent chimpanzee habitat with lots of food trees.

To the south is the Kalande community (also known as Bwavi). Most of the Kalande community’s range is grassland and woodland, with narrow strips of forest along the stream valleys. We know less about the Kalande chimpanzees than any of the others in Gombe. For the most part, these chimpanzees are still unhabituated, meaning they fear people. Researchers can follow the Kasekela and Mitumba chimpanzees around all day long, but they are lucky to get even fleeting glimpses of Kalande chimpanzees.

We aren’t even completely sure how many chimpanzees live in Kalande. Based on sightings and samples of genetically distinct individuals, there seem to be at least 9 chimpanzees in Kalande, but we don’t know for sure.

Skull from a male chimpanzee found dying in Kalande in 1994 or 1995.

A small team of researchers monitor the Kalande chimpanzees. They collect fecal samples for genetic analysis, which enables us to keep track of individuals, even when we don’t know what they look like. Kalande has the highest rate of infection with the virus SIVcpz, which likely contributed to the decline of this community (Rudicell et al., 2010). Many females have left Kalande for other communities, both as part of the natural emigration process (females usually leave to join a new community when they are sexually mature), and because as Kalande declined, it eventually came to have too few males. Females seem to prefer living in communities with many males, both because many males are better able to defend the feeding territories that females need to survive and raise their offspring, and because females need unrelated males as mating partners. As the number of adult males in Kalande dropped down to one, or perhaps even zero, some Kalande females left for good, while others seem to have kept their Kalande home base, but visit Kasekela for mating.

Kat and Kazi, photographed when visiting Kasekela (20 April 2006)

Kati, for example, is a Kalande resident who has probably lived there since 1998. Based on genetic data, we think she is the daughter of Patti who was known as Tita when she was younger. Since 2006, Kati has been making occasional visits to Kasekela. I saw her with her young son Kazi on one of these early visits. Of the Kalande chimps, Kati seems to fear people the least, which would make since if she grew up in Kasekela.

Deus and I took the boat to Kalande, where we met Ashaabu, one of the new Kalande research assistants. Ashaabu got his start working as a village Forest Monitor for his village’s forest reserve (part of the Greater Gombe Ecosystem project). Before going into the forest, we talked with Ashaabu for a while about which chimpanzees he has been seeing.

Kazi, who was just a little boy back in 2006, now seems to be the alpha male of Kalande, even though he is just a gawky adolescent. Based on how old Kazi looked back in 2006, I think he must be at least 12 years old now. Ashaabu says Kazi is around the size of the Kasekela male Fundi, who is about 14. The old male Renadi (or Leonard) hasn’t been seen for a number of years now, and I suppose must be dead. There might be another adolescent male, Pamera, but we don’t know for sure if he is still alive. Ashaabu has regularly seen Kati, Kazai, Katarina (Kati’s new baby), a big female without an infant, an adolescent female (who I think might be Pairott), and another young female around Kazi’s size. (Perhaps this is really Pamera? Might be hard to tell he’s a male if he’s still young and seen only briefly from a distance.) Ashaabu also mentioned Obedina, a female who had a big belly last year who might also have a new baby now.

After talking, we hiked into the forest, climbing a steep rocky path into Nyamagoma valley. Nyamagoma is the southernmost valley of the park, just north of Kazinga village. The path wound through an open woodland with a view of the lake below.

Along the way, we collected fruits and leaves for the isotope and nutrition projects. Given that Kalande has so much woodland, it will be interesting to see if the Kalande chimpanzees, or their foods, differ isotopically at all from those in Kasekela.

We followed the path down towards Nyamagoma Stream, where tall trees grew, shading the steep valley in green light. We didn’t see any chimpanzees, but we did see a number of nests. Chimpanzees build a new nest (or bed) in trees each night to sleep safely out of reach of any predators that might be lurking about. We found one cluster with five fresh nests, suggesting that up to seven chimpanzees might have slept there (if the group included Kati and Obedina and their new babies). It was encouraging to see so many fresh signs of chimpanzees using this valley. The Kalande community is still hanging in there, and perhaps they might recover, if the Kasekela males don’t catch Kazi and finish him off.

Ashaabu carried with him the tablet computer he had used as a Forest Monitor. He used the tablet to take pictures of the nests and enter the data, including GPS locations of the nests. It was quite stunning for me to think each of the villages around Gombe now has its own Forest Monitors, collecting data like this on their own village forest reserves, and loading it up regularly into the Cloud.

Director of Chimpanzee Research for Gombe Stream Research Centre.

Gombe, Isotopes, Nutrition

Isotopes and Isoptera

June 24, 2014 DaktaMaik 2 Comments

My main goal in visiting Gombe this trip was helping my graduate student, Rebecca Slepkov Nockerts, get started with her project on the stable isotope ecology of chimpanzees and baboons at Gombe.

Over the past couple of decades, stable isotope studies have revolutionized the study of the diets of human ancestors.

Isotopes are variants of chemical elements that differ only in the number of neutrons. For example, carbon has three naturally occurring isotopes, of which Carbon-12 (¹²C) is the most common. All carbon atoms have 6 protons – that’s what makes them carbon atoms, and not some other element. ¹²C has 6 protons and 6 neutrons, and is stable – each atom can last for billions of years. Carbon-14 (¹⁴C) is a radioactive isotope of carbon. It has 6 protons and 8 neutrons – which makes it unstable. It gradually decays, turning into Nitrogen-14 while spitting off an electron and an electron anti-neutrino. By geological standards, ¹⁴C decays relatively quickly, making it useful for dating objects containing carbon that are up to about 60,000 years old.

The third naturally occurring isotope of carbon, ¹³C, has 6 protons and 7 neutrons, and is stable, though much less common than ¹²C. For the most part, chemical reactions involve interactions among electrons, and to some extent protons. Neutrons don’t get involved. As a result. ¹³C behaves chemically almost exactly like ¹²C. However, in some reactions, the slightly different mass of the heavier isotopes can make a difference. For example, in photosynthesis, molecules containing ¹³C move more slowly, because they are heavier, and end up in different proportions in the final product.

As it turns out, several different major groups of plants use different mechanisms of photosynthesis, which produce distinct isotopic signatures. Especially important in paleoanthropology are C₃ plants (most plants, including most forest species) and C₄ plants (certain plants adapted to hot dry climates, including many tropical grasses and sedges).

Unfortunately, all of these different numbered C’s quickly get very confusing! But the main thing to remember is that C₃ = forest, C₄=grass. Chimpanzees mainly eat C₃ forest plants. Even in dry woodlands, chimpanzees eat mainly forest plants: fruit, seeds, flowers and leaves from trees, vines and shrubs growing along rivers and streams. In contrast, baboons eat more C₄ plants – especially grass seeds and corms. Similarly, stable isotope studies of fossils have found that early hominins ate mainly C₃plants (and/or animals that ate C₃plants), whereas later hominins at more C₄ plants (and/or animals that ate C₄ plants).

However, all of these inferences about hominin diet depend on some assumptions about how different tissues reflect diet. Unfortunately, studies comparing hominin isotope signatures to those of living species usually use different tissues. Studies of fossils usually use tooth enamel, which is extremely stable and thus is thought to maintain a good record of the living animal’s isotope signature for millions of years after death. Studies of living primates, however, usually use tissues that are easier to obtain, such as hair and feces, because it is hard to get tooth enamel from living animals (which are generally busy using their teeth). We therefore don’t know nearly enough about how diet translates to isotope signatures across these different tissues in living species. This is what Rebecca plans to find out.

Freud eating termites (02 Nov 2006) — Freud eating termites
(02 Nov 2006)

The long-term study of chimpanzees and baboons at Gombe brings together the key pieces needed for this study: expertise in identifying and collecting the important food species, long-term records on diet, and skeletons from known individuals. For example, we have a lifetime of data on chimpanzees like Freud, pictured here in November, 2006 eating termites.

Rebecca and Deus examining the bones of Freud the chimpanzee

Freud recently died, at nearly 43 years of age (making him one of the longest lived Gombe males). Thanks to concerted efforts over the years by people at Gombe Stream Research Centre, the skeletons of Freud and many other well known individual chimpanzees and baboons have been preserved. Thanks to a lifetime of data on these individuals, we know a lot about what they have been eating. This comprehensive data on individuals will provide an unparalleled amount of detail for matching up diet to isotope signatures of different tissues.

It is particularly interesting to look at chimpanzees and baboons at Gombe because these two quite similar species differ somewhat in their diets in ways that parallel some differences between early and later hominins: baboons eat more grass than chimpanzees, just as later hominins appear to have eaten more grass (and/or grass-eating animals) than earlier hominins.

Rebecca and baboons collecting grass samples

We are working together with Carson Murray and Rob O’Malley, who are conducting a nutritional study of chimpanzees. Both the nutritional study and the isotope study need foods to be collected, so we will work together to collect foods and share samples.

Rob did his PhD work at Gombe, studying insectivory by chimpanzees. Chimpanzees and baboons both eat a wide range of insects at Gombe.

On our first day in the field, we were lucky to catch an emergence of flying termites (“kumbi kumubi” in Swahili). These members of the infraorder Isoptera are one of the most important insect foods, not only for chimpanzees and baboons, but also many birds, monitor lizards, and even people.

We also found a nice column of Dorylus army ants (“siafu” in Swahili).

siafu jaws — Column of army ants showing off their jaws

Army ant soldier biting Rob's thumb. — Army ant soldier biting Rob’s thumb.

From an isotopic perspective, insects like termites and army ants may be interesting mainly for another isotope, Nitrogen, which provides information about where an animal gets its protein from. The higher the animal’s trophic level (the higher it is in the food chain), the more enriched its tissues are in the heavier Nitrogen isotope, ¹⁵N. It will be interesting to see whether chimpanzees and baboons at Gombe differ in their Nitrogen isotope signatures, and whether the isotopic signatures of individual chimpanzees relate to how much meat or insect matter they ate while alive.

At the night meeting, Rob and Rebecca explained their projects to the chimpanzee field staff. Rob talked about nutritional differences that he had found between ants and termites. I noted that “even people like to eat termites, right?” The field assistants responded with many people talking at once. The general consensus: “We like to eat termites, yes, but we like locusts even better!”

And I have to agree. Termite sauce with mushrooms is okay but seems a bit buggy to me, whereas fried locusts quite tasty.

Conservation, Gombe

Return of the Trees

June 20, 2014 DaktaMaik

04 June 2014

Gombe National Park is pretty remote. It is in the northwest corner of Tanzania, on the shores of the world’s longest and second deepest lake, Tanganyika. From the lakeshore at Gombe, you can see the hills of Burundi to the north and the mountains of Congo across the lake. It took me several days of travel, by train, plane and boat, to get to Gombe from our current home in France.

The research station at Gombe is only 22 km (14 miles) north of town, but because Gombe is surrounded by steep hills, you can’t drive there. Instead, we travel by boat, which usually takes 1.5 to 2 hours, depending on the conditions of the lake. The lake is often calm in the morning, but as the air heats up in the afternoon the lake gets choppier, until early evening when (usually) it starts to calm down again. We left town at 2:00 pm, with a heavily laden boat and rough water.

Having been away for two years, the biggest change I noticed was on the hills above the lakeshore villages. When I first visited Gombe in 2001, the hills outside the park were bare. Fields of cassava and beans were planted on slopes that seemed much too steep for agriculture. Red earth showed from erosion scars, including one in Mtanga village where a landslide in January 2001 killed 13 people.

Here’s a picture of Kazinga village, right at the southern boundary of the park, in August, 2005:

The park boundary runs along the crest of the hill, and apart from one big green mango on the ridge in the foreground, the trees end at the park. Just about everything on the slopes outside the park has been cut for firewood.

In contrast, here’s how the same ridge looks now. It’s early dry season so the grass is greener, and thus makes the contrast seem even starker. But even taking this into account, what surprised me was seeing lots of trees on the slopes outside the park. Where the forest used to end abruptly at the park border, now a blanket of forest drapes over the ridge, extending down towards the village. There aren’t trees everywhere, but even in Gombe the forest cover is intermixed with woodlands and grasslands, depending on the terrain and soil conditions. But that there are any noticeable trees at all outside the park is striking. The Jane Goodall Institute’s reforestation project really seems to be working.

It wasn’t just Kazinga village, either. Passing by many of the lakeshore villages I was struck at the contrast: steep hills were now blanketed in green trees instead of bare red earth. The photo at the top of this blog post is Kigalye village, which has an especially extensive forest reserve. The trees are coming back.

After I got to Gombe, Lilian Pintea showed me satellite images that confirmed what I had seen from the lake. Not just along the lakeshore, but extending all along the crest of the rift escarpment, trees were coming back. This was the interconnected network of village forest reserves that had been promised in the Greater Gombe Ecoystem project. It really is happening.

The deforestation of the village hills was a classic Tragedy of the Commons. The trees provide many public goods. Their roots hold the soil in place, preventing erosion and landslides and protecting the watershed so important for the streams, the main source of drinking water for the villages. The trees provide wood for cooking fires, furniture, boats, musical instruments and traditional carvings. Many of the trees produce fruit eaten not only by animals such as chimpanzees and baboons, but also by people. Their flowers enable bees to make honey. The leaves of the trees shade the ground, slowing evaporation, helping the soil retain moisture. But because the trees are common property of the village, as the human population grew, people cut the trees faster than they could grow back. Soon the villages suffered the public costs of deforestation: erosion, landslides, fouled drinking water, lack of wood for fuel and lumber, and the disappearance of plants valued for traditional medicine.

In 1994, the Jane Goodall Institute started the Lake Tanganyika Catchment Reforestation and Education Program (TACARE). Twenty years later, with help from many outside sources, including the Nature Conservancy and USAID, the project really does seem to be succeeding.

Will the project be a success in the long term? That really depends on the people living in the villages, and whether, as the years go by, they perceive the forests as providing net benefits to them. There will undoubtedly be cases of human-wildlife conflict. Animals living in the forest reserves may raid crops; and people might hunt the animals. As trees grow bigger, there will be strong temptations to cut the trees with valuable timber, and decisions will need to be made at the village level about how to manage these resources effectively. But seeing these trees growing has given me hope that these are solvable problems.

Evolution, Gombe, Health

Solving the origin of a major malaria parasite

March 4, 2014 DaktaMaik 1 Comment

A recent study by Beatrice Hahn and colleagues, published in Nature Communications, has solved a major puzzle about the origin of one of the parasites that causes malaria in people worldwide: Plasmodium vivax.

Malaria is one of the world’s deadliest diseases, killing perhaps a million people each year. Most of the people who die from malaria are in Africa, and most of them children. In areas where malaria is common, adults often have a degree of resistance to the disease, but still get sick enough now and then to miss many days of work, suffering from agonizing aches, fevers and chills. Even though most victims are children, many adults die as well, especially when their immune systems are weakened by other infections. Malaria thus has huge economic costs and has been cited as one of the main drags on economic growth for many tropical nations.

Malaria has had a huge impact on human history and evolution. Malaria is one of the major reasons that Africa resisted European colonialism for so long. Europeans visiting Africa died in droves until the discovery that a drug extracted from the bark of the South American cinchona tree, quinine, protects against malaria. Quinine is fairly awful stuff: when I took it to fight a particularly bad malaria infection, it caused vomiting and a painfully loud ringing of the ears. From the mid-20^th Century on, more effective anti-malarial drugs have been produced, which have helped many millions of people survive this terrible disease. Visiting and working in the tropics for business, tourism or, say, field primatology, would be a lot more dangerous without these drugs.

Before the discovery of such drugs, and for the many millions of people in poor countries who still don’t have adequate access to them, malaria has served as a powerful source of selection pressure on human populations. Because malaria is so deadly, human populations with long exposure to the disease have evolved a number of different defenses.

Malaria was originally thought to be caused by the “bad air” (Italian: “mala aria“) of swamps and marshlands. It is now known to be a group of similar disease caused by several different species of single-celled protozoans from the genus Plasmodium. Plasmodium falciparum is the most deadly, and the most common in Africa. Plasmodium vivax is more common in Asia. Because these parasites are different species, and only distantly related, tricks that work to defend against one species of parasite may not work agains the other.

The most famous anti-malarial adaptation is sickle-cell disease, which is caused by a single small change to a gene for hemoglobin, the protein that carries oxygen in red blood cells. This change changes the shape of the hemoglobin molecule.

Sickle cells in action. From: http://en.wikipedia.org/wiki/Sickle_cell

Red blood cells are packed full of hemoglobin, and if cells have only the abnormal hemoglobin, they become abnormally curved (shaped like a sickle or a crescent moon). People with one copy of the gene for sickle-cell disease have higher resistance to Plasmodium falciparum.

People with two copies of the gene, though, have sickle-shaped that cells get stuck going through narrow capillaries, causing all sorts of problems, which shortened life expectancy before the development of modern medical treatments.

Falciparum malaria is such a dangerous disease that having improved resistance more than offsets the risks of having children whose lives are shortened by inheriting two copies of the gene.

Nonetheless, sickle-cell trait seems a rather clumsy solution to the problem. Kind of like using hand grenades to protect yourself from tigers. The grenades can stop tigers fine, if you can throw them far enough. But if you don’t throw them far enough, they blow up too close and kill you instead. Perhaps sickle-cell is an emergency stop-gap measure that evolved too recently for all the kinks to be worked out yet.

A seemingly better solution to this sort of problem is the Duffy-negative trait, which provides resistance to a different species (Plasmodium vivax), with little apparent cost to people who have the trait.

To understand the tricks that have evolved to defend against different species of Plasmodia, it is useful to know something about the life cycles of these parasites. These life cycles are complex and involves different stages of sexual and asexual reproduction in various organs of different hosts, including the human liver, human red blood cells, mosquito guts, and mosquito salivary glands.

Malaria parasite life cycle. From: http://www.niaid.nih.gov/topics/malaria/pages/lifecycle.aspx

The malaria life cycle is a complicated solution to problems of replication, sex, and dispersal of Plasmodium genes. In most animals that we are familiar with, such as ourselves, individual organisms do the major work of replication, sex and dispersal. As individual organisms, we accomplish these goals by mating, raising kids, and sending them off to college, for example.

Malaria parasites have found ways to outsource most of this work to other organisms. To replicate, they turn human hosts into giant malaria factories, turning red blood cells into production centers that burst, releasing newly produced parasites into the blood stream, infecting new red blood cells, in an exponentially increasing production system that destroys millions of the host’s red blood cells. This is the part of malaria where the human host feels weak and miserable and suffers from alternating fevers and chills.

Most of this replication phase is asexual: making millions of copies of the same thing. This works fine within a single host, but if you want your babies to survive in the cruel and variable outside world, you need to boost their chances by introducing variation into their genes through sex. So towards the end of the cycle, the parasites start making male and female versions, the gametocytes. When mosquitoes suck the blood of an infected host, they suck up these gametocytes, which can then have sex with gametocytes picked up from other hosts. The offspring of the gametocytes then infest the mosquitoes gut, eventually sending sporocytes to the salivary glands, so they get injected into the next person the mosquito bites, starting the cycle over again. The mosquito thus serves as both a malaria parasite dating service and dispersal system. Kind of like college.

Anyway, a key part of the malaria parasites life cycle is getting into the host’s red blood cells. To do that, they use specific proteins on the surface of the blood cell, which serve to transport certain chemical signals across the cell membrane. Plasmodium vivax parasites use one specific kind of protein, the Duffy antigen receptor, to force their way into human red blood cells. In much of Africa, the indigenous people don’t have this receptor. There is thus no way for P. vivax to infect them. People who don’t have the Duffy antigen receptor may suffer some costs, such as increased susceptibility to asthma, but these costs don’t seem to be anywhere near as high as those imposed by sickle-cell trait. And of course they are much less than the costs of dying from malaria.

The African distribution of the Duffy-negative phenotype has been a puzzle, though, because P. vivax is very rare in Africa. The conventional wisdom has been that P. vivax evolved in Asia. How could a parasite that evolved in Asia, and is rare in Africa, select for parasite resistance in Africans? This would be as puzzling as if people in Africa were all born with some sort of inherent immunity to tiger attacks, even though there are no tigers in Africa.

Beatrice Hahn and her team have solved the problem by collecting poop from thousands of apes across Africa. I played a very small part in this study, by overseeing poop collection for a while at Gombe.

Humans are apes, and many diseases that infect humans can also infect other apes, or (like in the case of HIV) originally came from other apes. Malaria is no exception. On a molecular scale, we are so similar to chimpanzees and gorillas that the tricks pathogens use for getting into human cells often work for these cells in other apes as well.

Beatrice Hahn’s team has been collecting fecal samples from apes all across Africa as part of a study looking into the origins of HIV-1, the cause of the global AIDS pandemic. It turns out that the same samples, and same molecular methods, that are so useful for studying HIV, are equally useful for studying all sorts of other things that live inside humans and other apes, including other viruses and gut microbes.

It turns out that when apes are infected with malaria, they shed some of the malaria DNA out with their poop. Take some poop, put it in a jar of RNAlater, and you can recover all sorts of fascinating genes, including malaria genes.

(When Jimmy Fallon and Justin Timberlake visited Gombe some years ago, they seemed amused by all of our poop collection and made up a song about it: “Poop in a Jar.” Disappointingly, though, they don’t seem to have recorded this one yet.)

It turns out that gorillas and chimpanzees across Africa, but not bonobos, have malaria parasites that genetically are very close to Plasmodium vivax. Compared to the gorilla and chimpanzee parasites, the human vivax is much less genetically diverse. All the human P. vivax belongs to a single branch of the much bushier tree of African ape P. vivax.

It thus looks very clear that P. vivax evolved in Africa, not in Asia, from a plasmodium population that infects other African apes. People must have carried P. vivax with them when dispersing from Africa some 60,000 years ago. More recently, human populations in Africa evolved the Duffy-negative phenotype that proved so effective that P. vivax became extinct in Africa.

This study underscores the importance of evolution in human lives. Evolution happens fast, and human populations continue to evolve in response to our environments. The parasites that infect us evolve even faster. Evolution leaves traces in the genomes of every living organism that can be used to solve innumerable fascinating puzzles. This study highlights the power of molecular methods to answer important questions, especially when combined with field studies.

Gombe, Life Histories

Frodo (30 June 1976 – 10 November 2013)

January 19, 2014 DaktaMaik 5 Comments

Several of my blog posts have featured Frodo, the iconic alpha male chimpanzee of Gombe National Park. Frodo also figures prominently in several of my research papers, given that he has been a major player in aggression at Gombe, both within his own community, and during attacks on the neighbors. I’m sorry to report that Frodo died on Sunday, 10 November 2013. Perhaps fittingly, given Frodo’s aggressive behavior in life, aggression seems to have contributed to his death. Necropsy revealed that he had a scarred scrotum and infected testis, probably due to what seems to have been a canine puncture wound received in August 2013. As ye sow, so shall ye reap. [Edit (23 May 2022): subsequent results from pathology indicated that Frodo died from renal failure, not from infection from his scrotal wound.]

Jane Goodall named Frodo for the noble, humble, diminutive hobbit from the Lord of the Rings, which she had been reading to her son. From a cute little baby chimpanzee, Frodo grew to be a hulking brute, a despotic alpha male, and a fearless hunter of monkeys.

Frodo was born on 30 June 1976, the second of Fifi’s nine offspring. Fifi was a highly successful mother and was for many years the highest-ranking female of Gombe’s Kasekela community. As an infant, Frodo proved mischievous, disrupting Jane Goodall’s efforts to record data on mother-infant relationships by grabbing at her notebooks and binoculars. As he grew older, Frodo developed a habit of throwing rocks, charging at, hitting, and knocking over human researchers and tourists. In 1988, Frodo grabbed and pulled at cartoonist Gary Larson’s arm when he visited Gombe, and the next year Frodo severely beat Goodall herself.

In his prime, Frodo weighed 55 kg (121 lbs), larger and stronger than any of his peers. Frodo rose quickly in the ranks as he matured and won the position of alpha male by overthrowing his brother Freud in October, 1997. Frodo reigned as alpha male for 5 years, until weakened by sickness in December 2002. We knew the game was up for Frodo when he gave submissive pant-grunts to the next alpha male, Sheldon, in January 2003.

As alpha male, Frodo ruled by brute force. Unlike his brother Freud, who frequently groomed lower ranking males in apparent efforts to win their support, Frodo rarely groomed any other males, but instead frequently presented himself to be groomed by them.

Frodo competed vigorously for mating opportunities throughout his life, fathering his first offspring, Zeus, when he was 17, and his last, Samwise, when he was 25. He even forced his attention on his own mother, fathering an infant, Fred, who lived for less than a year before dying in a mange epidemic. Frodo fathered both of Gremlin’s twins, Golden and Glitta, the only wild chimpanzee twins known to have survived to adulthood. Frodo’s son Titan follows in his father’s footsteps by throwing rocks at baboons, chimpanzees and people, and has recently challenged the current alpha male. In total, Frodo fathered eight offspring, more than any other male at Gombe but Wilkie (who fathered 10). Frodo’s offspring were born to six different females: Trezia, Patti, Gremlin, his own mother Fifi, Sparrow and her daughter Sandi.

After being deposed in 2003, Frodo spent months by himself recovering, and when he rejoined the other males he had fallen to low rank. He continued to show keen interest in competing for mates and hunting monkeys, but he mellowed considerably, and in his last years rarely showed any signs of aggression towards people.

Frodo was the first chimpanzee that I saw in Gombe, and I recognized him instantly, with his silvery grey back, the round ruff of silvery hair framing his face, and his large size. Frodo taught me what life is like for most chimpanzees: you must constantly be aware of where the alpha male is, because he might charge any time, and may beat you up. The first time he came charging past me, I wondered why everyone was running away; as a kid I had read George Schaller’s descriptions of gorillas, and how when they charged you must stand your ground, and only people who ran got bitten. I assumed the same must be true for chimps. And sure enough, when I studied chimpanzees for my dissertation research in Kibale Forest, Uganda, the alpha male Imoso would simply veer around me if I got in his way, acting as if that was what he meant to do. But not Frodo. He saw that I wasn’t moving and went straight at me, knocking me into the bushes. He beat on me briefly with his fists, but in a surprisingly gentle way. He could have easily done real damange, but he acted as if his only goal was to show me who was boss. Him.

My next day in the forest, I was extremely wary of Frodo. I managed to avoid him for most of the morning. However, during a hunt, someone else ended up with the carcass of a redtail monkey, and Frodo was angry. He charged around, displaying. He charged past a whole line of researchers to get to me, where he knocked me into the bushes yet again.

That was the last time that Frodo bothered me, though. He seemed to accept that I was part of the gang of people that followed him and his community all around the forest, and that I sufficiently acknowledged his magnificence.

Frodo resting on the trail in June, 2009.

Frodo was one of several F-family chimpanzees that rose to high status. Most of Fifi’s offspring that survived to maturity rose to high ranks, with three of them becoming alpha male: Frodo’s older brother Freud, Frodo himself, and the current alpha male, Ferdinand. Fifi’s daughter Flossi is one of the highest ranking females in the Mitumba community. Frodo is survived by four sons (Zeus, Titan, Tarzan, and Sindbad), three daughters (Golden, Glitta, and Samwise), his brothers Freud, Faustino, and Ferdinand, sisters Fanni, Flossi, Flirt at least two grandchildren, and numerous nephews and nieces.

Frodo grooming his daughter Glitter (June 2012).

Researchers and filmmakers followed Frodo throughout his life, making him one of the most thoroughly documented wild chimpanzees in history. Numerous books and scientific articles described Frodo’s success as a hunter, fighter, and alpha male. Frodo first appeared in films as an infant in People of the Forest: The Chimps of Gombe (1991, Discovery Channel). Frodo knocks presenter Charlotte Uhlenbroeck off her feet in The New Chimpanzees (1995, National Geographic). The films Fifi’s Boys (1996, BBC) and Chimpanzee Diary (1997, BBC) depict Frodo’s rising power and rivalry with Freud. Frodo dominated the giant screen feature Jane Goodall’s Wild Chimpanzees (2002, Imax), filmed at the peak of his powers. More recently, Frodo was featured in The Dark Side of Chimpanzees (2004, BBC), Return to Gombe (2004, Discovery Channel) and Chimpanzee Family Fortunes (BBC, 2006).

Gombe just won’t feel the same with Frodo gone.

Gombe, Intergroup Conflict

Hunting and Fighting

June 13, 2013 DaktaMaik

In chimpanzees, intergroup aggression and hunting look quite similar in several ways. Both hunts and intergroup attacks are mainly the business of males. In both cases, groups of males climb, leap, and run after a victim, which, if they catch, they will bite and pummel until it stops moving. Attacking males bristle their hair like fighting cats, making them look even bigger than they really are. They bare their teeth in fearful grimaces and scream.

Red colobus leaping to escape chimpanzees.

Since the 1970s, researchers have speculated that hunting and fighting in chimpanzees are related, resulting, perhaps, from the same psychological mechanisms. For example, chimpanzees’ close relatives, bonobos, have not been observed to kill other bonobos, and bonobos rarely hunt. Perhaps the two behaviors are linked? For example, my thesis advisor Richard Wrangham has speculated that as bonobos evolved from a chimpanzee-like ancestor, “males lost their demonism, becoming less aggressive to each other. In so doing, perhaps they lost their lust for hunting monkeys, too.” (Wrangham & Peterson 1996: 219)

Ten years ago, when I was a post-doc with Anne Pusey, in the early stages of extracting records on intergroup aggression from the long-term data at Gombe, I looked at seasonal patterns of intergroup encounters, as part of an effort to understand why such encounters occurred. From the limited sample of years for which I’d extracted data, intergroup encounters occurred most often in the late dry season (September and October) with a smaller spike in the middle of the wet season (February). When I compared notes with Anne’s graduate student, Ian Gilby, I was struck that he had found essentially the same pattern with hunts: the number of hunt attempts per follow peaked in the late dry season and mid wet season. Additionally, comparing five years for which we both had data, we found that years with more hunting success also had more patrols. Was this because hunting and intergroup fighting were caused by the same factors?

We agreed we should work on this further, and now that work has born fruit: a forthcoming paper in Animal Behaviour by Gilby, Wilson and Pusey.

A key inspiration for this work was one male chimpanzee, Frodo. Frodo was the best hunter at Gombe when Ian was doing his dissertation research. Frodo was involved in all four intergroup killings that I described in my first Gombe paper (Wilson et al., 2004). I had watched video, frame by frame, of Frodo brutally attacking a young male chimpanzee from the Kalande community. Maybe Frodo was a great hunter because he was a great fighter? Frodo was also exceptionally persistent in pursuit of estrous females, and genetic studies found that Frodo had fathered more babies than any other Gombe male. I began to wonder if in chimpanzees, hunting and fighting were both byproducts of selection for skills needed to achieve mating success.

Male red colobus jumping down to chase chimps — Male red colobus monkey jumping down to chase Titan, Fundi and Frodo.

Ian kept Frodo very much in mind when he went on to work as a post-doc with Richard Wrangham on data from Kanyawara. Ian proposed that a key part of group hunting in chimpanzees was the presence of particular individuals who really liked to hunt – which Ian termed “impact males.” As a group-level activity, hunting suffers from potential collective action problems. Hunting is risky and dangerous. Red colobus monkeys don’t want themselves or their babies to get eaten, and they fight back fiercely, biting with their sharp teeth. Individuals therefore might be tempted to free-ride – let others do the hunting, and then get meat afterwards, by begging, stealing, or scavenging what’s left when others are done eating. But if everyone free-rides, no one will hunt. So how does hunting get started? Ian proposed that some individuals, the impact males, are strongly motivated to hunt – and once they get started, others are encouraged to join in, because the costs of joining a hunt already in progress are less than the costs of starting the hunt.

Titan, Fundi and Frodo looking at red colobus monkeys, deciding whether to hunt.

The logic of “impact males” made sense to me, not only for hunts, but also for territorial behavior. Patrolling boundaries is energetically expensive and potentially dangerous, as patrols can meet a big group of hostile neighbors. Patrols therefore seem vulnerable to the same collective action problems as hunts. So maybe they are solved the way: some individual males are strongly motivated to go on patrols, reducing the costs for everyone else to join in. After all, if I know at least one of my buddies is going on patrol, I know I won’t be alone at the edge if I go with him. And perhaps – maybe these are all correlated for the same reason? Maybe the same males are impact hunters and impact patrollers? And maybe these same males are the ones who are really good at winning dominance interactions, gaining high rank, and getting access to fertile females and fathering lots of babies? Maybe these are all correlated traits, parts of an overall personality profile or behavioral syndrome of what it takes to be a successful male chimpanzee?

We now had lots more data to work with than we did a decade ago: 32 years of data on both hunting and boundary patrols. And we found that hunting and patrolling boundaries were indeed correlated, not just on a monthly basis, but also on a daily basis. However, it turned out that hunting and patrolling were mainly correlated because of the influence of other variables. Both hunting and patrolling were more common when males were in large parties – which we expected, because parties with more males are more likely to succeed, both in hunts and in intergroup encounters. But the main reason hunting and patrolling were correlated was because both involved long-distance travel. When chimpanzees patrol their borders, they necessarily travel a long ways. And when they travel a long ways, they are more likely to encounter monkeys.

We found that there were indeed impact males for both hunting and patrolling. But only one of the males who was an impact hunter was also an impact patroller. And surprisingly, good old Frodo was neither an impact hunter nor patroller. He had a positive impact on hunting probability, but not enough to merit status as an impact hunter. And the probability of patrolling was the same, with and without Frodo in the party.

So these results suggest that hunting and fighting, despite their many resemblances, may result from different psychological mechanisms. In some ways this is not really surprising, given that in species whose brains have been studied in detail, such as rats and cats, aggression and predation involve quite different regions of the brain. Additionally, Marissa Sobolewski has looked in detail at the hormones of male chimpanzees from the Ngogo community, going on two different kinds of patrols: hunting patrols, in which males are looking for monkeys, and border patrols, in which males are presumably looking for neighbors. Marissa found that testosterone levels were elevated for border patrols, but NOT for hunting patrols. This strongly suggests that hunting and fighting do indeed result from different psychological mechanisms in chimpanzees.

Our findings from the long-term data are thus rather different from what we thought we’d find. This illustrates the importance of looking at data, not just theory, when doing science. It’s easy to fall in love with hypotheses, but they need to stand the test of empirical work. Nonetheless, I still suspect there may be interesting links in the psychology of hunting and fighting. For example, tendencies towards pugnaciousness and risk-seeking seem likely to benefit both hunting and fighting (and acquiring mates). But from the data we’ve examined so far, being a top hunter doesn’t automatically make one an influential boundary patroller.

(For more on Frodo, see Ian’s biography of Frodo, Lisa O’Bryan’s description of Frodo in retirement and this picture of baby Frodo.)

Gombe, Guassa, Mpala

Global Positioning Systems

June 18, 2012 DaktaMaik

Saturday, 16 June 2012

According to the GPS map on the little screen on the seat in front of me, we’re flying over the North Atlantic now, midway between the spot where the Titanic went down in 1912, and the Corner Seamounts.

Usually when I fly to Africa, the first leg is a flight to Europe, usually overnight. Then, after an early morning layover in London, Brussels or Amsterdam, we board a southbound plane that flies all day to Nairobi, Entebbe, or Dar es Salaam. But today we’re flying on a Boeing 787, which can fly straight to Africa on a single tank of fuel. And instead of taking off in the afternoon or evening and flying overnight, we left Washington Dulles in the morning. After some 13 hours in the plane, we’ll arrive in Addis Ababa Sunday morning.

While much of the routine is familiar, there have been many changes over the past 20 years. When I first flew to Africa, they showed movies on a few small, dim screens in the forward section of the cabin. Now the back of every seat has its own screen with a choice of movies, television, and GPS maps.

It’s fun to watch the plane slowly crawl across the world on the GPS map. Twenty years ago, GPS technology was just becoming available for civilian use. Towards the end of my time in Kenya, Jeanne Altmann brought a GPS unit to Mpala to help map the baboon ranging patterns. It was an expensive, bulky, heavy box, and in those days the US government scrambled the signal so that all locations would be off by an unknown number of meters. But it pinpointed locations in a magical way. At the time, I had been drawing range maps onto photocopies of a map of the study area, estimating location with reference to map features like the meandering wall of the cliff, which snaked along in parallel to the Ewaso Ng’iro river, and the streams, roads, and bomas (corrals for cattle and sheep). When we got up into the plateau above the escarpment, landmarks disappeared, and my estimations of where we had gone got worse and worse. A GPS would have been nice to have!

All these new gadgets, like GPS wristwatches and handheld units with global terrain maps, make it seem like the field of primatology has moved quite slowly in comparison. We still do basically the same thing: following primates around, watching what they do, recording behavior as systematically as we can, trying to answer research questions that really haven’t changed all that much from the 1970s: Why do animals live in the sorts of social groups that they do? What explains differences in behavior between males and females? How does that relate to their ecology?

The questions are simple to state but hard to answer. Ecology, evolution and behavior are all complicated, with lots of moving parts, and it can take many years to get enough data on enough individuals to answer key questions. But even the field does move rather slowly, new tools like GPS technology have helped greatly. We can track locations precisely now. And just like in real estate, the three most important things in much of behavioral ecology are location, location, and location. Animals need food, safety, water, and mates, and the availability of all these key resources vary in space and time.

At Mpala, each day the baboons traveled a circuit, leaving the safety of the sleeping cliffs in the morning to search for food and returning to safety for the night. One of my favorite parts of studying baboons in Kenya was arriving at the top of the sleeping cliffs before dawn to watch the sun rise over Mount Kenya. The baboons seemed to enjoy the view too, basking in the sun’s rays to warm up from the cool night before starting their day’s search for food. But where to go? How do they decide? How does a group of 50 or 60 quarrelsome monkeys pick a path for the day?

Mike following baboons at Mpala — Following baboons at Mpala research camp, Kenya, in 1993

Answering questions like these requires lots of good location data. And now they’ve got GPS units small enough to go on radio collars, enabling researchers to watch the daily paths of baboons and other animals, just as I’m watching the plane on the screen on the seat in front of me creep closer and closer to Africa.

monkey business