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Baboon-Trackers Herald New Age of Animal Behaviour Research

Picture a troop of olive baboons, moving over the savannah. There’s around fifty of them, and they cover a lot of ground as they search for grass, seeds, insects, and other bits of food. They need to stick together so they don’t get eaten, but different animals might want to head in different directions at any one time. How do they coordinate their choices to preserve the sanctity of their group? As primate researcher Joan Silk says, “It’s hard enough to get two adults and two kids into the car at the same time let alone 50 baboons who can’t talk.”

It’s a fairly simple question—how do animals make decisions as a group?—but it’s also incredibly hard to answer, even for animals like baboons that have been actively studied since the 1950s. A field-worker can easily track a single baboon, or even a few. But she can’t track all 50 at once, let alone note down who’s getting up, who’s leading, and who’s following, over long periods of time.

She can, however, turn to technology. By fitting wild olive baboons with sophisticated GPS collars, which automatically record their movements, Margaret Crofoot from University of California, Davis had learned exactly how they make decisions about where to go and whom to follow. Some of her results are surprising, others are more intuitive; regardless, her study heralds a new age of zoology, in which scientists can analyse animal behaviours on a scale that was previously impossible.

For several years, Crofoot had been using radio-trackers on wild capuchin monkeys, to study how they fend off predators and fight other monkeys as a group. “I was getting increasingly interested in how individual decisions scale up to group behaviours,” she says, “but you can’t watch everyone at once.” Then, she heard about the collars.

GPS collars aren’t new but they often have poor temporal resolution. They might take a reading once every few hours, for example—good enough to track a migrating bird. Newer models are much more sensitive and can take readings once a second—good enough to track a running cheetah. “I thought, wow, if you could put these collars on primates, you could do all these studies on an intact social group, living in its natural habitat,” says Crofoot.

Olive baboons were an obvious choice. They’re well-studied, so their behaviours can be interpreted in the light of decades of knowledge. They live in open habitats, where GPS signals are strong and good. And unlike many other monkeys which scamper through trees, baboons live on the ground, making them easier to follow, trap, and collar.

A troop of olive baboons. Credit: Stig Nygaard
A troop of olive baboons. Credit: Stig Nygaard CC-BY-2.0

The hardest bit was actually finding the right troop. Many researchers have spent a lot of time in habituating baboons to their presence, and they were concerned that trapping the individuals would wreck that hard-earned tolerance. So Crofoot worked with a troop in Kenya’s Mpala Research Centre, which weren’t part in any other studies. Over a week, her team caught and collared 25 of the individuals.

Once the data were in, team members Ariana Strandburg-Peshkin and Damien Farine worked together to interpret it. They wrote a programme that would automatically identify events where, say, one baboon walked off and others followed, or when one walked off and then returned to the same spot. The video below shows 25 minutes of movements, sped up 25 times.

Surprisingly, they found that a baboon’s rank in the pecking order didn’t affect its odds of being followed. Rank matters a lot in baboon society, and affects how much sex, food, and support each individual gets. When making foraging decisions, the dominant males wield a despotic hold over the rest of the group, enforcing choices even when they’re the wrong ones.

But when it comes to more mundane decisions like “Where should we go?”, their tyrannical sway isn’t evident. The data revealed that the troop members didn’t weigh the movements of dominants any more heavily than those of subordinates. Age and sex didn’t matter either. “It’s a little surprising that dominants aren’t using their social power to drive group decision in ways that are beneficial to them,” says Crofoot. “It seems that on a day-to-day level, most decisions are made more democratically.”

The team also showed that what happens if baboons have differences of opinion. If two baboons move off in different directions, but at the same time, the angle between their paths determines what the others do. If that angle is small—say, less than 90 degrees—other baboons will split the difference and head off in the average direction. If the angle is big, the followers make a choice, and trail one initiator or the other.

That’s rather astonishing—not because of the rule, but because it exactly follows what Iain Couzin from Princeton University predicted a decade earlier, using just mathematical theory and computer simulations. Couzin, a leader in the field of collective behaviour and a collaborator in Crofoot’s study, modelled the movements of animal groups, creating digital swarms in which individuals were all the same and had no special relationships. By contrast, identities and relationships are paramount in baboon society. And still, “the simple model predicted the behaviour of the very complex social group,” says Crofoot. “We were really struck by just how closely the patterns matched.”

“It’s a great study, and really innovative,” says Joan Silk from the University of California, Los Angeles. “We’ve been perplexed for many, many years about how animals in groups figure out where to go next, and how the process of group movement is coordinated and negotiated. It’s been impossible to quantify the movement patterns of multiple individuals at the same time. But now, we can do this.”

This is just the beginning. The team have uploaded their gargantuan pile of data to Movebank—a free, online database of animal tracking data—so that others can have a play. They also have plans for more analyses of their own.

For example, Strandburg-Peshkin says that individuals baboons do vary in their odds of being followed—it’s just that this variation doesn’t correlate with anything obvious like sex, age, or dominance. What then? What makes one animal a likelier leader and another not? Is it something about where they sit in the group, in physical space rather than social hierarchy? For that matter, what determines where individuals sit, and how do their positions change as the group shifts and moves? And what happens when a stationary group decides to travel? “How do you overcome the inertia of whole bunch of baboons sitting around?” asks Crofoot.

Strandburg-Peshkin also notes that they only looked at data from one baboon troop, and she’d like to know if other groups—or other animals—show the same patterns. A decade ago, that would have been wishful thinking. Now, with improvements in GPS collars, flight trackers, and related tech, it’s a plausible expectation. We’re entering a new age in the study of animal behaviour.

But don’t neglect fieldwork! By casting their actual eyes and ears into the wild, researchers can understand the social structure and behavioural quirks of their animals—information that no collars can provide. The trick will be to marry that hard-won, old-fashioned knowledge with the world of big data. “That would be the dream,” says Strandburg-Peshkin.

“Most behavioural research on wild baboons requires years of study and yields very little data,” says Andrew King from Swansea University, who has done more work on baboons than most. “This study is an excellent example of how we can generate lots of data very quickly to complement long-term observational studies.”

“We are using similar tracking collars to understand baboon behaviour and ecology in Namibia and South Africa,” he adds. “The next few years will be a lot of fun.”

Reference: Strandburg-Peshkin, Farine, Couzin & Crofoot. 2015. Shared decision-making drives collective movement in wild baboons. Science http://dx.doi.org/10.1126/science.aaa5099

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On the Origin of Colourful Monkey Faces

“Can you hear that?” says James Higham.

I can. It’s a loud screeching noise in the background of our phone call.

“That’s a female rhesus freaking out,” he says.

Rhesus macaques have featured heavily in lab experiments, but this particular loud female is part of a wild group, living in Puerto Rico. Higham, an anthropologist from New York University, is studying them. He is interested in their faces, which vary from a dull pink to a vivid red. Specifically, he wants to know if the females judge the males on the intensity of that colour.

“I’m stood about 5 metres away from a sub-adult male and he’s with a 3-year-old female, and they’ve been mating a lot,” he says. “There are lots of other monkeys here, and the big, blue Caribbean sea around me.” As field work goes, it’s not hard.

The same couldn’t be said for the other group of funky-faced monkeys that Higham has been studying—the guenons. These African monkeys are known for their beautiful and diverse faces. De Brazza’s monkey has a white moustache and beard, and an orange sun rising on its forehead. The crowned guenon: dark eyeshadow, a black quiff, a pair of white forehead highlights, and a luxurious golden beard. The red-eared guenon: a drunk’s pink nose, a black brow ridge, white tufts around its eyes, and—yes—red ears. Every species of guenon, and there are between 24 and 36 of them, has its own distinctive facial marks.


In the 1980, zoologist James Kingdon suggested that they recognise members of their own species by their faces. Many of these monkeys live in the same place, and some travel in large mixed groups. They live, feed, and watch out for predators together, but when it comes time to mate, their faces help them to find partners of their own kind.

The idea made sense; testing it has been difficult. For a start, guenons live in forest canopies and move quickly. It’s hard to look at their faces, let alone look at them looking at each other’s faces.

Their patterns are also complicated, so how do you objectively compare them? If two guenons have yellow sideburns and pink noses, but differently shaped brows and differently coloured eyes, are they similar? A bit different? Very different? Humans are terrible at this kind of task; we have to limit ourselves to comparing specific features, which Kingdon found frustrating.

Higham opted for a different approach. He and postdoc William Allen took hundreds of photos of 22 guenon species in various zoos and wildlife sanctuaries, and analysed them with the eigenface technique—a facial recognition programme developed in the 1980s. It can quantify how distinctive two faces are by comparing them across many features simultaneously.

The technique revealed that guenon species have more distinctive faces when they live together. This supports Kingdon’s hypothesis that the colourful facial palettes help neighbouring monkeys to recognise their own kind, despite sharing the same forests. By contrast, if the faces were adaptations to something in the monkeys’ environment—say, light levels—then species that live together should look more similar. In fact, it’s the opposite.

Next, Higham and Allen wanted to know if the monkeys could glean any more information from each other’s faces. Could guenons tell each other’s age or gender? Could they recognise individuals, as we humans can?

The duo used a computer programme to analyse 541 images from the same photo set, on the basis of either overall patterns or specific features—like the brightness, colour, shape, or size of their eyebrows and nose spots. They wanted to see if the programme could, based on these traits, classify the monkeys by species, age or gender, or recognise individuals. For example, after seeing photos of different monkeys, could the programme accurately identify one in a new photo? Likewise, after seeing photos of monkeys of both genders, could it tell if a new monkey was male or female?

The programme flunked the age and gender tests—there’s apparently nothing in a guenon’s face that reveals either characteristic. But it excelled at both species and individual recognition. The former isn’t surprising but the latter is.

As Kingdon suggested and Higham confirmed, guenons have evolved to look as different as possible when they live together. The need for differences between species ought to constrain the differences within them. “If you start looking very different from others of your species, you run the risk of being mistaken for something else,” says Higham. This kind of “stabilising selection” should lead to distinctive species but lookalike individuals—and yet that’s not what he found. One guenon can potentially tell its neighbours apart with a glance.

Of course, there’s no guarantee that what the programme is seeing is what the guenons actually see. Higham is now carrying out some experiments to see if the differences that the computer can glean are actually obvious to the monkeys themselves. He has even played around with drones to see if he can get a closer view of the guenons as they clamber through the canopy.

In the meantime, he thinks that his methods will be broadly useful to scientists who study animal signals. “There’s a lot of work on colour signals in animals and a lot of it is quite simple, like: This lizard patch varies from pale pink to bright pink,” he says. “But a lot of these signals are very complex. So, how do you measure them?” Computer learning offers an option. “That’s true whether it’s a guenon or a paper wasp or a paradise flycatcher or anything really.”

References: Allen, Stevens & Higham. 2014. Character displacement of Cercopithecini primate visual signals. Nature Communications. http://dx.doi.org/10.1038/ncomms5266

Allen & Higham. 2015. Assessing the potential information content of multicomponent visual signals: A machine learning approach. Proc Roy Soc B. http://dx.doi.org/10.1098/rspb.2014.2284


When Monkeys Surfed to South America

Long ago, about 36 million years before today, a raft of monkeys found themselves adrift in the Atlantic. They’d been blown out to sea by an intense storm that had ripped up the African coast, and now a mat of floating vegetation was the closest thing to land for miles in all directions. But luck was with them. Thanks to a favorable current, they were thrown onto the beach of a new continent – South America.

I’ll admit that this scenario requires a little scientifically-informed imagination. No one has ever found a fossilized huddle of monkeys clinging to battered vegetation in ancient ocean sediments. But we know that such events must have happened in the past. Teeth tell the tale.

In the latest issue of Nature, paleontologist Mariano Bond and colleagues describe a handful of fossil teeth found in the rainforest of Peru. Some are mysteries, too incomplete to identify down to genus or species, but a set of three molars are clearly from a new species of early monkey.

Three teeth might not seem like much to name a new animal, but, fortunately for paleontologists, mammals have always had very distinct teeth that tend to get fossilized even when the rest of the body decays. From the cusps and ridges, Bond and coauthors were able to narrow down the identity of this animal to a monkey that was about the size of a modern day tamarin. They’ve named it Perupithecus ucayaliensis.

At about 36 million years old, Perupithecus pushes back the arrival of monkeys on South America 10 million years earlier than previously thought. And even better, the molars of Perupithecus closely resemble those of Talahpithecus – an early monkey that lived around the same time in northern Africa. This doesn’t mean that Perupithecus was directly descended from Talahpithecus. Rather, it’s a another strong sign that the ancestors of New World monkeys were accidental migrants from Africa.

Perupithecus, or its immediate ancestors, probably arrived on rafts of storm-tossed vegetation. There wasn’t an overland route for the primates to make the same journey. Even though South America and Africa were once connected, they had drifted apart by 110 million years ago – long before the evolution of primates, much less monkeys. South America stayed an island continent from then until its collision with Panama about 3 million years ago. There was no other way from monkeys to get from Africa to South America except by sea. The monkeys that thrive in the Americas today, from tamarins to muriquis, are the descendants of prehistoric primates fortunate enough to survive the journey.


Bond, M., Tejedor, M., Campbell, K., Chornogubsky, L., Novo, N., Goin, F. 2015. Eocene primates of South America and the African origins of New World monkeys. Nature. doi: 10.1038/nature14120

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Monkeys With Better Social Networks Stay Warmer in the Winter

It’s three in the morning in South Africa, in the middle of winter. Temperatures have dropped to just below freezing and a vervet monkey—silver-furred and black-faced—is very, very cold. Soon, the rising sun will heat the land to a much nicer 25 Celsius, but for now, the vervet faces five hours of bitter chill. So, it seeks out some friends for warmth. And as they huddle together in a shivering heap, tiny thermometers in their bodies record their temperatures.

Richard McFarland from the University of the Witwatersrand implanted the devices in a dozen vervets in January 2011. His goal: to see if their social ties could help these wild animals to cope with wildly varying temperatures.

McFarland is no stranger to such research. In 2008, he studied two groups of Barbary macaques—stocky, stump-tailed monkeys, living wild in Morocco’s Atlas Mountains. He found that those with more social ties were more likely to survive the winter of 2008—an exceptionally cold and snowy season that killed 30 of them. It was the first study to show that an animal’s social connections can affect its odds of surviving a bout with the elements. The question was: why?

One possibility was that the well-connected macaques were better at keeping warm, because they could more easily find partners to huddle with or could huddle in bigger groups.

To test that idea, McFarland’s team travelled to the opposite end of Africa. They tranquilised a dozen female vervets and surgically implanted wax-sealed temperature recorders into their abdomens. When the monkeys came to, the team released them and counted how many social partners they had—that is, how many other vervets they groomed and were groomed by. Nineteen months later, the team recovered the recorders and the precious data they contained.

The data revealed that during winter, the monkeys’ core temperatures were often three degrees lower at night than in the day. As the months wore on, these fluctuations became increasingly severe. But the more partners the monkeys had, the steadier their body temperatures were. Sociability meant stability.

These results put a new twist on the value of group-living among primates. In some now-classic studies, Joan Silk from the University of California, Los Angeles, showed that young baboons are more likely to survive if their mothers have strong social bonds. There could be many reasons for this, but one popular idea is that such bonds help animals to deal with stress. Certainly, well-connected monkeys have lower stress hormones than isolated ones, and that alone might give their immune systems a break, and improve their survival. The same applies to humans—people with bigger social networks tend to have better physical and mental health.

But the vervets show that social ties have another important benefit. “Better-networked monkeys stay warmer in winter,” says Katie Hinde from Harvard University, who was not involved in the study. “That has the potential to protect animals from illness and leave them with more calories for building babies.”

And unlike Silk’s baboons, “it’s not just strong bonds that matter,” says Louise Barrett from the University of Lethbridge, who led the research. “Weak bonds matter too. Having a lot of partners that you can call on means you can have a bigger huddle, or find a partner if yours is already busy. There’s a utilitarian function to maintaining a lot of bonds.” In other words, quantity matters as much as quality. This effect might even be important in keeping a vervet group together, and stopping its members from splintering into smaller factions of tightly knit—but very cold—individuals.

Huddling isn’t the only way in which groups stay warm, either. Vervets cement their friendships by grooming each other, and that improves the insulating properties of their fur. “It’s like fluffing a duvet,” says Barrett.

“I think this study has important implications for the behavioural ecology of personality,” adds Hinde. She wants to know the vervets’ personality traits affect their social networks and how that, in turn, affects their survival and reproductive success. Do gregarious monkeys stay warmer than live longer than loners? And how does that vary between parts of Africa with different climates? In regions where temperatures swing more manically throughout the day, do monkeys have better social integration?

Reference: McFarland, Fuller, Hetem, Mitchell, Maloney, Henzi & Barrett. 2015. Social integration confers thermal benefits in a gregarious primate. Journal of Animal Ecology http://dx.doi.org/10.1111/1365-2656.12329

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Two New Fossils Reveal Details of Ape/Monkey Split

In 2011, a team of palaeontologists led by Nancy Stevens, unearthed a single molar in Tanzania’s Rukwa Rift Basin. It was a tiny fossil, but its distinctive crests, cusps and clefts told Stevens that it belonged to a new species. What’s more, it belonged to the oldest known Old World monkey—the group that includes modern baboons, macaques and more. They called it Nsungwepithecus.

A year later, and 15 kilometres away, the team struck palaeontological gold again. They found another jawbone fragment, this one containing four teeth. Again, a new species. And again, an old and distinctive one. The teeth represent the oldest fossils of any hominoid or ‘ape’. They called it Rukwapithecus.

Together, these two new species fill in an important gap in primate evolution. Based on the genes of living species, we know that Old World monkeys and apes must have diverged from each other between 25 and 30 million years ago. But until now, there weren’t any fossils from either group during that window. The ones we found were all 20 million years old or younger.

But Nsungwepithecus and Rukwapithecus were both found in sediments that could be precisely dated to 25.2 million years ago. They imply that apes had already split away from Old World monkeys by that time. Finally, fossils had corroborated the story that genes were telling. And they suggested that the split between these two groups took place against a backdrop of geological upheaval.

I wrote about the discoveries for The Scientist so head over there for the full story.

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On Copycat Whales, Conformist Monkeys and Animal Cultures

This is the story of a whale that tried something new and a monkey that fell in line.

It’s about how wild animals can create cultures and traditions just as we can, through the twin forces of innovation and conformity.


Lunge-feeding humpbak whale, by Jennifer Allen and the Whale Center of New England
Lunge-feeding humpbak whale, by Jennifer Allen and the Whale Center of New England

In 1980, a humpback whale in the Gulf of Maine started doing something different. All its neighbours would catch small fish by swimming in circles below them, blowing curtains of bubbles, and then lunging straight up at the corralled shoal. Then one individual, out of the blue, started smacking the water surface with its tail before diving down and blowing its bubbles.

This behaviour is called lobtail feeding, and no one knows why it works. Maybe it disturbs the water above the bubble curtains and discourages fish from jumping to safety. Whatever the benefit, it went viral. Just eight years after the first innovative whale started doing it, 20 percent of the Maine humpbacks had picked up the technique. Now, it’s more like 40 percent. What began as one whale slapping the water is now a tradition.

The obvious explanation is that the whales were learning from each other. But there could be other reasons. If the technique has a strong genetic basis, it could pass down family lines without any form of social learning. Or maybe environmental changes were responsible. The whales seem to use lobtail feeding specifically to catch small fish called sand lance, and the strategy only started spreading after populations of herring, another important prey species, crashed. Perhaps hunger drove the whales to individually develop a new technique for catching a different sort of prey.

Jenny Allen worked out how to tell these possibilities apart. As a masters’ student, she had worked on whale-watching boats in Maine, and knew that the Whale Center of New England (WCNE) had collected a huge data set of the local animals’ behaviour. Over 27 years, they had recorded almost 74,000 sightings. Allen was looking for ways of using this data when she joined Luke Rendell’s lab at the University of St Andrews as a PhD student. “I realised this was the lobtail-feeding population and asked whether it was still going on,” says Rendell. “She said, ‘Yes, it seemed to still be spreading’. I knew we were in business.”

The team used the Maine data to reconstructed the whales’ social network and simulate the spread of lobtail feeding under different mathematical models—some that included social learning and others that didn’t. The results were so clear that even Rendell was surprised. “It was very, very clear that cultural transmission was important in the spread of the behaviour,” he says.

The models which assumed that the whales were learning lobtail feeding from each other were a far better fit for the actual spread of the behaviour than those which assumed no social connection. “The weight of evidence was up to 23 orders of magnitude greater for these models,” says Rendell. “It’s the difference between the weight of a single person and the weight of planet Earth.”

By contrast, genetics was unimportant. “Having a lobtail-feeding mother makes virtually no difference to whether you will become one,” says Rendell. Ecology mattered more. Whales were more likely to learn the lobtail method in the specific region where the sand lances live, and during years when sand lance numbers were high.

This doesn’t detract from the importance of social learning, which was by far the more important factor in the strategy’s spread. Instead, it shows how useful it can be to pick up skills from your neighbours. “If a species is smart enough to innovate and transfer information socially, it could adapt very quickly to new environmental  pressures. This is why humans are so successful,” says Michael Kruetzen from the University of Zurich. “I find this to be a highly convincing case for a foraging tradition in a cetacean,” adds Susan Perry, an anthropologist from the University of California, Los Angeles.

Critics might point out that Allen’s study relied only on observations rather than experiments, and incomplete observations that were limited by what boat crew could see. But the team took steps to account for this, adjusting their models to account for patchy sightings, or the fact that the most commonly spotted whales would repeatedly pull off the same behaviours. None of that changed the results.

And Rendell scoffs at the notion that you can never know anything for sure from observational data alone. “It would be great to look at this experimentally, but we’re talking about a population of wild humpback whales here,” he says. “Spock and Kirk were able to beam one up in The Voyage Home, but we aren’t going to be doing that any time soon. This is really the best approach we have, and the answer it gives is unequivocal.”


Vervet monkeys choosing pink corn over blue. Credit: Erica van der Waal
Vervet monkeys choosing pink corn over blue. Credit: Erica van der Waal

Meanwhile, thousands of miles away in South Africa’s Mawana Game Reserve, there lived a vervet monkey called Groot, who was a fan of blue corn. One day, two boxes of dyed corn kernels had mysteriously appeared. The pink ones tasted disgusting but the blue ones were tasty, and Groot’s entire group quickly learned to eat the blue ones. Then, as all male vervets do when they grow up, Groot left his family behind and moved to a new group. And when he did, he saw that his new companions liked pink corn instead.  He watched, he processed, and he starting eating the pink corn too.

Groot didn’t know it, but he was part of an ambitious experiment by Erica van de Waal and Andrew Whiten from the University of St Andrews to study the spread of animal traditions. Recently, Whiten’s team has studied whether captive chimps and capuchin monkeys can learn from each other. The answer is yes. Tutors, who are taught new foraging techniques in isolation, can seed their groups with these new innovations when they are reunited.

This approach is impractical in the wild, because it’s very hard to isolate a tutor individual. Instead, scientists have studied differences in behaviour between groups of wild chimps, orang-utans and other species. These studies have been pivotal for our understanding of animal culture, but they’ve run against the same refrain that Rendell dislikes: they’re just observational, not experimental.

So, van de Waal tried something new—she seeded new traditions in entire groups rather than individuals. She gave four groups of wild vervets, which included 109 individuals between them, a choice between blue corn and pink corn. In each case, the group would only ever eat one colour because the other was coated with a repulsive extract from local aloe plants. (They tried vinegar and chilli powder, but the vervets happily ate those. Only aloe worked. “The experimenters tested the corn themselves and had the bitter taste for a whole day in their mouths,” said Whiten.)

Van de Waal took the corn away for 4 to 6 months and during that time, new babies were born into the vervet communities. The corn eventually returned and this time, both colours were tasty and palatable. Even so, it seems you can’t teach an old vervet new tricks, and the monkeys stuck with their existing colour preference.

More importantly, their infants, who had never seen dyed corn before, just ate whatever they saw their mothers eating. Those born into pink cultures ate pink corn. Those born into blue cultures ate blue corn.

It’s not surprising that infants follow their mothers, but the strength of their preferences caught the team off-guard. “Infants chose only what their mother ate despite there being right in front of them a box of perfectly edible corn of a different colour,” says Whiten. “Some even sat on that, to eat the ‘right’ colour of corn!”

Emigrating males also took up the traditions of their new groups. By sheer luck, during the experiment, ten males moved into a group that preferred a different coloured corn than their original group did. Seven of these newcomers seven immediately started eating whatever colour their new comrades preferred, and two more soon followed suit. The only exception was a male called Lekker who immediately took up a dominant rank in his new group, which may explain why he stuck to his old ways.

Perry praises the elegant experiments but notes that the numbers are quite small. “Seven out of ten is only 2 data points greater than chance preference for a particular colour,” she says. “I appreciate the difficulty in obtaining a larger sample—you have to wait for males to migrate—but I hope the authors will persevere in increasing that sample size.”

This degree of conformity is surprising especially for vervets, which “are often thought to be opportunistic”, according to Whiten. This “when-in-Rome” mentality makes sense. In the wild, foraging animals have to make decisions about the nutritional quality of potential foods and the presence of poisons. When moving into a new environment, it pays to copy what local experts are doing, even when it means overriding the knowledge you’ve gained in a different context.

The tendency to conform could also explain other social learning experiments have failed. Scientists have tried to teach new behaviours to wild tutor individuals, including vervets and meerkats, but found that these nascent traditions are difficult to spread. That may be because these traditions face an uphill struggle, says Whiten, “whereas, in our study, the naïve infants and immigrant males were already surrounded by a majority doing the same thing.”

The team now wants to see if the wild vervets will also learn more complicated behaviours from each other, such as techniques for dealing with their food. Based on work with captive monkeys, they think the answer is yes. It’s now time to take these experiments into the field.


Thanks to decades of research, it is now clear that animals can learn from each other in ways that create different cultures in the wild.

As Frans de Waal writes in a commentary accompanying these new studies, “The early debate about animal culture focused on the mechanism of behavioural transmission.” Are apes apeing each other in the way that humans can? When whales and dolphins imitate each others’ songs and actions, do they understand each others’ goals and methods? When blue tits peck open the tops of milk bottles, is it because they’ve picked up the technique from other tits, or because those birds just drew their attention to the bottles?

Now, studies of animal culture are moving beyond just asking whether it happens to probing why it happens and how strongly it does. The humpbacks show that new traditions can easily spread within a group, but the vervets show that the conformity can also suppress new behaviours in favour of old rituals. We see the same tension between innovation and conformity in our own societies, and it’s fascinating to see the same patterns in animal groups.

All of this requires intensive field work and long-term studies. To watch the vervets from the comfort of nearby chairs, de Waal and Whiten had to spend over a year with the monkeys, getting them used to their presence and learning how to recognise over 100 individuals by eye. To understand what the whales were doing, Allen and Rendell had to use a 27-year set of data. “That shows how important it is to have long-term research so you can create these data sets,” says Kruetzen “If people had just gone there for a year or two, it would have been very hard to document these changes.”

Reference: Allen, Weinrich, Hoppitt & Rendell. 2013. Network-Based Diffusion Analysis Reveals Cultural Transmission of Lobtail Feeding in Humpback Whales. Science http://dx.doi.org/10.1126/science.1231976

Van de Waal, Borgeaud & Whiten. 2013. Potent Social Learning and Conformity Shape a Wild Primates Foraging Decisions. Science http://dx.doi.org/10.1126/science.1232769

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The Bruce effect – why some pregnant monkeys abort when new males arrive

On a grassy Ethiopian plateau, revolution and death are underway. The plateau is home to a group of geladas – shaggy, grass-eating, and occasionally terrifying relatives of baboons. They’re like a cross between a cow, Animal from the Muppets, and your nightmares.

Geladas live in units where a single dominant male lords over several related females, whom he monopolises as mates. It’s an enviable position, and males often have to fend off takeover bids by eager bachelors. If a newcomer ousts the chief monkey, it’s bad news for the group’s females. A wave of death sweeps through the unit, as the new male kills all the youngsters whom his predecessor fathered. Indeed, babies are 32 times more likely to die after a takeover than at any other time.

But that’s not all. Eila Roberts from the University of Michigan has found that the new male’s arrival triggers a wave of spontaneous abortions. Within weeks, the vast majority of the local females terminate their pregnancies. It’s the first time that this strategy has been observed in the wild.


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Larger monkey groups lose fights because they contain more deserters

In the Battle of Rorke’s Drift, 150 or so British troops defended a mission station against thousands of Zulu warriors. At the Battle of Thermopylae, around 7,000 Greeks successfully held back a Persian army of hundreds of thousands for seven days. Human history has many examples of a small force defeating or holding their own against a much larger one.

Among animals too, the underdogs often become the victors. One such example exists in the rainforests of Panama. There, capuchin monkeys live in large groups, each with its own territory. The monkeys often invade each other’s land. Numbers provide an obvious advantage in such conflicts, but small groups can often successfully defend their territory against big ones. Unlike human underdogs, they don’t win because of superior tactics or weapons. They win because their rivals are full of deserters.


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English monkey gives itself a pedicure with self-made tools

Animals use tools to get food, communicate with one another, defend themselves or even have a scratch. But in Chester Zoo, England, one monkey uses tools to give itself a pedicure.

Riccardo Pansini and Jan de Ruiter from Durham University watched a 18-year-old mandrill called JC clean his toenails out using small splinters. He made them himself, fashioning them from wood chips and twigs on the floor his enclosure, and honing them till they were small and sharp.


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What is the point of pruney fingers?

The common wisdom is that your fingers wrinkle when they’re wet because they absorb water. But Mark Changizi thinks there’s more to it than that. According to him, pruney fingers are an adaptation to help humans, and probably other primates, get a better grip during wet conditions. They act like the rain treads on tyres. Mark lays out his hypothesis in a wonderful paper that I wrote up as a news story for Nature News.

Here’s the start; click through for the whole thing.

The wrinkles that develop on wet fingers could be an adaptation to give us better grip in slippery conditions, the latest theory suggests.

The hypothesis, from Mark Changizi, an evolutionary neurobiologist at 2AI Labs in Boise, Idaho, and his colleagues goes against the common belief that fingers turn prune-like simply because they absorb water.

Changizi thinks that the wrinkles act like rain treads on tyres. They create channels that allow water to drain away as we press our fingertips on to wet surfaces. This allows the fingers to make greater contact with a wet surface, giving them a better grip.

Scientists have known since the mid-1930s that water wrinkles do not form if the nerves in a finger are severed, implying that they are controlled by the nervous system.

“I stumbled upon these nearly century-old papers and they immediately suggested to me that pruney fingers are functional,” says Changizi. “I discussed the mystery with my student Romann Weber, who said, ‘Could they be rain treads?’ ‘Brilliant!’ was my reply.”

Reference: Changizi, Weber, Kotecha, & Palazzo. Brain Behav. Evol. http://dx.doi.org/10.1159/000328223 (2011).

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Our closest relatives – a visual tour of the primates

Few groups of animals hold such special significance for us as the primates – the apes, monkeys, lemurs and more. This is the group that we are a part of. Its members are familiar and charismatic, but our evolutionary history is tangled and occasionally controversial.

Now, Polina Perelman has provided the most comprehensive view of the primate family tree to date. Her team sequenced genes from over 186 species, representing 90% of all the genera that we know of. Her tree confirms some past ideas about primate evolution and clarifies other controversies. It’s a story of island conquests, shrinking bodies, tangled branches and ancient relics.

Image by Medeis

Today, the primates’ closest living relatives are the flying lemurs, or colugos, of Southeast Asia. There are two species that both glide between trees, using flaps of skin outstretched between their legs. They can’t actually fly and they’re not really lemurs, making them the second most inaccurately named animal, after Michael Winner.

Flying lemurs aside, our next closest relatives are the treeshrews, which also live in Southeast Asia. Continuing the theme of inaccurate names, they aren’t true shrews, but they do at least (largely) live in trees.

By me

The oldest fossil primates, such as Plesiadapis (pictured), lived around 56 million years ago, but genetic studies suggest that the group may have arisen even earlier than that. Perelman says that her study provides “strong evidence” that the first primates arose from a common ancestor around 90 million years ago. That was around the middle of the Cretaceous period, when dinosaurs like Tyrannosaurus and Triceratops were still around. It’s not clear where the primates first arose but Asia’s the best guess, given that the flying lemurs, treeshrews and many of the earliest primates are all confined there.

No sooner had the primate family tree established itself than it split into two major trunks, around 87 million years ago. The first group – the wet-nosed strepsirrhines – include lemurs, lorises and bushbabies. We belong to the other group, the dry-nosed haplorrhines, which also includes tarsiers, monkeys and other apes.

Images by Kalyan Varma (slender loris, left), OpenCage (Senegal bushbaby, middle), Visionholder (black-and-white ruffed lemur, right)

Once they had split away from the haplorrhines, the strepsirrhines themselves diverged into two major lineages around 69 million years ago. The first gave rise to the Lorisiformes, a group that includes the slow-deliberate lorises and pottos, and the spectacular leaping bushbabies. They diversified around 40 million years ago.

The second lineage gave rise to the Chiromyiformes, solely represented today by the bizarre aye-aye, and the Lemuriformes, which include all other lemurs. There are more than a hundred species and subspecies of lemur and they all live on the island of Madagascar. Every one of them descended from a common ancestor that washed up on the island’s shores around 59 million years ago.

Image by David Haring

The slow lorises have the dubious honour of being the only poisonous primates. A gland on the inside of their elbows secretes a poison that smells a bit like sweaty socks; the loris licks this gland, which gives it a toxic (and agonising) bite. The protein behind the poison is remarkably similar to the one that causes cat allergies.

The lorises as a group have another honour. Perelman found that they are the most divergent of all the primates. If you compared the genes of the seven or so species, you’d see differences that are 4 to 5 times greater than those between humans, chimps, gorillas and orangutans. For now, no one knows why.

Image by Frank Vassen

Carl Zimmer once described the aye-aye to me as a “furry Gollum”. This unusual creature is the most ancient of all the lemurs. Its ancestors were among the first to split away from the main lemur line after it arrived on Madagascar. It hunts for grubs at night by tapping on tree trunks with its grossly distended middle finger and listening out with large ears. If it hears the right sounds, it gnaws away at the bark with rodent-like teeth and hauls the grub out with the same narrow finger, wielded like a hook.

Images by me (ring-tailed lemurs; left), Erik Patel (indri; middle) and Arjan Haverkamp (gray mouse lemur, right)

The aye-aye aside, the remaining lemurs diverged into four main groups, starting 39 million years ago. The Lemuridae or so-called “true lemurs” were the first to emerge – today, they include the sociable and distinctive ring-tailed lemurs (left). The Indriidae were next – they include the group’s largest and most vocal member, the indri (middle), as well as the woolly lemurs and the agile, bounding sifakas. The remaining lineage split into the sportive lemurs (Lepilemuridae), and the dwarf and mouse lemurs (Cheirogaleidae; right). The latter include the smallest members of the group. Madame Berthe’s mouse lemur is the smallest of them all – it can weigh as little as 30 grams.

Image by Nummymuffin (golden lion tamarin)

While the strepsirrhines were diversifying, so too were the haplorrhines. The tarsiers were the first to branch away, around 81 million years ago (more on them in the next slide). The rest of the group (the Simiformes or “simians”) split into two main lineages around 44 million years ago. These were the “flat-nosed” platyrrhines (New World monkeys) and the “narrow-nosed” catarrhines (Old World monkeys and apes).

Image by Jasper Greek Golangco

The tarsiers have been a particularly difficult group to place. Originally, they were grouped together with the strepsirrhines to form the prosimians, from the Greek meaning “before ape”. This group – essentially all primates except monkeys and apes – has less relevance today, because we know that the tarsiers are actually haplorrhines. Perelman’s study confirms that.

These big-eyed, knobbly-fingered animals are found only in the Philippines and three Indonesia islands. But around 50 million years ago, there were tarsiers all over the Northern Hemisphere. Today’s species are but a shadow of a once diverse group, one that branched off early from other primates and has evolved alongside us ever since.

Images by Ipaat (bald uakari; top left), Mila Zinkova (emperor tamarin, top right); Luc Viatour (squirrel monkey, bottom left) Hans Hillewaert (mantled howler monkey, bottom right)

Modern platyrrhines live in Central and South America but it’s not entirely clear how their common ancestor got there. At the time, around 25 million years ago, the Panama land bridge that connected North and South American hadn’t formed, and the Atlantic Ocean was narrower. It’s possible that this ancient monkey rafted across from Africa. No matter how it got there, what happened next is clearer thanks to Perelman’s study.

After they reached South America, the platyrrhines diverged into three major families. The first to branch off were the pithecids, including the titis, the bald-faced uakaris (top left), the bearded sakis. Next came the atelids with their long, prehensile tails, including the howler (bottom right), spider and woolly monkeys.

Finally, the cebids. This group includes several species that have previously been classified in separate families; Perelman has decided to united them in one. They diverged in quick succession – first, the capuchins and squirrel monkeys (bottom left), and then, the marmosets, tamarins (top right) and the mysterious owl monkey.

Image by John Morton

The cebids are particularly interesting because as they diverged, they also became smaller. The group’s earliest members, including the night monkey and capuchins are generally larger than the later marmosets and tamarins. The smallest of the them all – the pygmy marmoset, no bigger than a hand – is also the latest to evolve.

Image by Mark Laidre

Meanwhile, in the Old World, the catarrhines had also diverged into three major families. The cercopithecoids, including all the Asian and African monkeys, branched away 32 million years ago and started truly diversifying around 18 million years ago. The remaining catarrhines split into two groups just 20 million years ago – the hylobatids, including all the gibbons; and the hominids, including ourselves and the other great apes.

The history of the cercopithecoids is a convoluted puzzle, not least because the genetic differences within the group are lower than expected. As they evolved, it seems that many subspecies and species mated with one another to produce hybrid lineages. They turned a neat forking tree into a tangled bush.

Images by Lea Maimone (mantled colobus, far left), Thomas Schoch (Hanuman langur, left), Benhamint444 (proboscis monkey, right), Jack Hynes (golden snub-nosed monkey, far right)

Despite the complex history of the cercopithecoids, Perelman thinks that the family splits into two big sub-families. The Colobinae started diversifying around 12 million years ago, but they’ve given rise to a large number of African and Asian species. Most of them live in trees and eat leaves These include the colobus monkeys (far left), the langurs and leaf monkeys (left), and the aptly-named “odd-nosed monkeys” (including the bizarre proboscis monkey (right) and China’s beautiful golden snub-nosed monkey (far right)).

Images by Hans Hillewaert (De Brazza’s monkey, far left) Muhammad Mahdi Karim (crab-eating macaque, left), me (hamadryaz baboon, right) Malene Thyssen (mandrill, far right)

The second cercopithecoid subfamily – confusingly known as the Cercopithecinae – diversified at around the same time as the Colobinae. They split into two tribes. One includes some of Africa’s most beautiful species including the guenons, patas monkey, green monkeys and vervets. The other includes baboons, geladas, mangabeys, mandrills and macaques. This second group in particular has a rich history of hybridisation.

Image by Suneko

They hylobatids, or gibbons, diversified by 9 million years ago and today, there are around a dozen or so species. The largest of them – the siamang – is pictured above. These “lesser apes” have taken the primates’ fondness for trees to a whole new level. Their wrist is made up of a ball-and-socket joint, much like our shoulders or hips. That means a swinging gibbon can rotate its entire body around its wrist, giving them a unique style of movement called brachiation (video). They can zoom through treetops with a top speed of 35 miles per hour.

While the gibbons’ movements are all style and grace, their chromosomes are a chaotic mess. They’ve rearranged around 10-20 times faster than most other mammals and, as with lorises, it’s not clear why. That’s a mystery for a future study to solve.

Images by me (orangutan, far left), Pierre Fidenci (bonobo, left), Mila Zinkova (gorilla, right) Ikiwaner (chimpanzee, far right)

Finally, we come to our small branch of the primate family tree – the hominids. If you follow the forking branches to us, the orangutan subfamily (Ponginae) were the first to split away around 16.5 million years ago. That branch later diverged into the two modern species of orangutan – the Bornean and Sumatran – just over one million years ago. On the other subfamily (Homininae), the gorillas were the next to branch away around 8.3 million years ago. Finally, our ancestors diverged from those of chimpanzees and bonobos around 6.6 million years ago.

The genus Homo has been around for less than 10% of the entire history of the primate order. And it has taken us far less time to put many of the other species at risk of extinction. Nearly half of all species are endangered thanks to a combination of deforestation, bushmeat hunting and illegal wildlife trade.


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Playing by the same rules reduces the differences between humans, chimps and monkeys

You’ve been asked to compete against some of your friends in a game of skill, but you realise something is amiss. They’ve been given precise instructions and details about the game’s mechanics. You’ve been given a couple of pieces and left to figure things out on your own. On this uneven playing field, no one could fairly compare your performance with that of your friends. This seems obvious, but it’s a problem that plagues a lot of research into the behaviour of humans and other animals.

Scientists will often test monkeys and apes with tweaked versions of psychological games that were originally designed to test humans. The goal is simple: understand the similarities and differences between our mental abilities and those of our closest relatives.

But these comparisons are tricky. Frans de Waal, who studies the behaviour of apes and monkeys, says, “Humans are tested by their own species and the apes by a different species (us). Humans understand everything the experimenter says or explains, whereas the ape needs to figure these things out based on experience. The paradigm really doesn’t permit the comparisons that have been made, especially the negative assessment of ape capacities.”

Sarah Brosnan form Georgia State University agrees. “As humans, we surely design tasks that are more intuitive to us than to other species. We don’t know whether humans perform differently from other species absent these advantages. Are human-specific abilities, including language, added ‘on top’ of other primate abilities, making us fundamentally similar in our outcomes. Or are we fundamentally different from the rest of the primates?”


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Do new discoveries ever “rewrite evolutionary history”?


You can’t go for a month without seeing a claim that some new discovery has rewritten evolutionary history. If headlines are to be believed, phylogeny – the business of drawing family trees between different species – is an etch-a-sketch science. No sooner are family trees drawn before they’re rearranged. It’s easy to rile against these seemingly sensationalist claims, but James Tarver from the University of Bristol has found that the reality is more complex.

Tarver focused on two popular groups of animals – dinosaurs and catarrhines, a group of primates that includes humans, apes and all monkeys from Asia and Africa. Together with Phil Donoghue and Mike Benton, Tarver looked at how the evolutionary trees for these two groups have changed over the last 200 years. They found that the catarrhine tree is far more stable than that of the dinosaurs. For the latter group, claims about new fossils that rewrite evolutionary history (while still arguably hyperbolic) have the ring of truth about them.


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Boom-boom-krak-oo – Campbell’s monkeys combine just six ‘words’ into rich vocabulary

Many human languages achieve great diversity by combining basic words into compound ones – German is a classic example of this. We’re not the only species that does this. Campbell’s monkeys have just six basic types of calls but they have combined them into one of the richest and most sophisticated of animal vocabularies.

By chaining calls together in ways that drastically alter their meaning, they can communicate to each other about other falling trees, rival groups, harmless animals and potential threats. They can signal the presence of an unspecified threat, a leopard or an eagle, and even how imminent the danger is. It’s a front-runner for the most complex example of animal “proto-grammar” so far discovered.

Many studies have shown that the chirps and shrieks of monkeys are rich in information, ever since Dorothy Cheney and Robert Seyfarth’s seminal research on vervet monkeys. They showed that vervets have specific calls for different predators – eagles, leopards and snakes – and they’ll take specific evasive manoeuvres when they hear each alarm.

Campbell’s monkeys have been equally well-studied. Scientists used to think that they made two basic calls – booms and hacks – and that the latter were predator alarms. Others then discovered that the order of the calls matters, so adding a boom before a hack cancels out the predator message. It also turned out that there were five distinct types of hack, including some that were modified with an -oo suffix. So Campbell’s monkeys not only have a wider repertoire of calls than previously thought, but they can also combine them in meaningful ways.

Now, we know that the males make six different types of calls, comically described as boom (B), krak (K), krak-oo (K+), hok (H), hok-oo (H+) and wak-oo (W+). To decipher their meaning,  Karim Ouattara spent 20 months in the Ivory Coast’s Tai National Park studying the wild Campbell’s monkeys from six different groups. Each consists of a single adult male together with several females and youngsters. And it’s the males he focused on.

With no danger in sight, males make three call sequences. The first – a pair of booms – is made when the monkey is far away from the group and can’t see them. It’s a summons that draws the rest of the group towards him. Adding a krak-oo to the end of the boom pair changes its meaning. Rather than “Come here”, the signal now means “Watch out for that branch”. Whenever the males cried “Boom-boom-krak-oo”, other monkeys knew that there were falling trees or branches around (or fighting monkeys overhead that could easily lead to falling vegetation). 

Interspersing the booms and krak-oos with some hok-oos changes the meaning yet again. This call means “Prepare for battle”, and it’s used when rival groups or strange males have showed up. In line with this translation, the hok-oo calls are used far more often towards the edge of the monkeys’ territories than they are in the centre. The most important thing about this is that hok-oo is essentially meaningless. The monkeys never say it in isolation – they only use it to change the meaning of another call.

But the most complex calls are reserved for threats. When males know that danger is afoot but don’t have a visual sighting (usually because they’ve heard a suspicious growl or an alarm from other monkeys), they make a few krak-oos. 

If they know it’s a crowned eagle that endangers the group, they combine krak-oo and wak-oo calls. And if they can actually see the bird, they add hoks and hok-oos into the mix – these extra components tell other monkeys that the peril is real and very urgent.  Leopard alarms were always composed of kraks, and sometimes krak-oos. Here, it’s the proportion of kraks that signals the imminence of danger – the males don’t make any if they’ve just heard leopard noises, but they krak away if they actually see the cat. 

The most important part of these results is the fact that calls are ordered in very specific ways. So boom-boom-krak-oo means a falling branch, but boom-krak-oo-boom means nothing. Some sequences act as units that can be chained together to more complicated ones – just as humans use words, clauses and sentences. They can change meaning by adding meaningless calls onto meaningful ones (BBK+ for falling wood but BBK+H+ for neighbours) or by chaining meaningful sequences together (K+K+ means leopard but W+K+ means eagle).

It’s tempting to think that monkeys have hidden linguistic depths to rival those of humans but as Ouattara says, “This system pales in contrast to the communicative power of grammar.” They monkeys’ repertoire may be rich, but it’s still relatively limited and they don’t take full advantage of their vocabulary. They can create new meanings by chaining calls together, but never by inverting their order (e.g. KB rather than BK).  Our language is also symbolic. I can tell you about monkeys even though none are currently scampering about my living room, but Ouattara only found that Campbell’s monkeys “talk” about things that they actually see.

Nonetheless, you have to start somewhere, and the complexities of human syntax probably have their evolutionary origins in these sorts of call combinations. So far, the vocabulary of Campbell’s monkeys far outstrips those of other species, but this may simply reflect differences in research efforts. Other studies have started to find complex vocabularies in other forest-dwellers like Diana monkeys and putty-nosed monkeys. Ouattara thinks that forest life, with many predators and low visibility, may have provided strong evolutionary pressures for monkeys to develop particularly sophisticated vocal skills.

And there are probably hidden depths to the sequences of monkey calls that we haven’t even begun to peer into yet. For instance, what calls do female Campbell’s monkeys make? Even for the males, the meanings in this study only become apparent after months of intensive field work and detailed statistical analysis. The variations that happen on a call-by-call basis still remain a mystery to us. The effect would be like looking at Jane Austen’s oeuvre and concluding, “It appears that these sentences signify the presence of posh people”.

Reference: PNAS doi:10.1073/pnas.0908118106

More on monkey business (clearly, I need more headline variation):