Mysterious Mandrills

The world’s largest and most colorful monkey species may also be the most elusive; scientists in Gabon only now are beginning to understand its social life and behavior

  • Michael Lipske
  • Mar 10, 2010

MALE MANDRILLS, LARGE MONKEYS of the Central African rain forest, are the world’s hottest-hued mammals, their “resplendent colors,” according to Charles Darwin, ranking “with those of the most brilliant birds.” Mandrills usually travel in groups numbering in the hundreds—the largest of any primate except humans—and females emit piercing screams to keep in touch as they move. With their color, numbers and noise, mandrills should be easy to find, but ecologist Kate Abernethy of Scotland’s University of Stirling, who has studied mandrills in Gabon’s Lopé National Park for 10 years, found that the species is ever elusive, challenging her efforts to learn more about it. Photographer Fiona Rogers, who has sought to capture images of mandrills in Lopé, also attests to the monkeys’ skill as escape artists: “If they have any inkling that you are near, whether they smell you, hear you, see you, they will run in the opposite direction at phenomenal speed.”

No one has looked at mandrills more thoroughly than Abernethy and her colleagues. Using video to record the size and composition of mandrill groups, called hordes, as they cross roads or clearings, and depending on radio collars to keep tabs on dozens of individual mandrills, Abernethy has shown that much of what had been ‘known’ about the species was wrong.

Hordes are composed mostly of female and juvenile mandrills, with only a small proportion of adult males in the crowd. In fact, adult male mandrills spend much of each year entirely alone in the forest, in what Abernethy has described as “monkish solitude.” Only at the onset of breeding season (roughly June to November in Lopé) do they join a horde.

When they do show up, mature males cannot be missed. Standing 3 feet tall and averaging almost 70 pounds, male mandrills are the largest of monkeys (they outweigh females up to four times). And they have a voice to match their swaggering presence. From dawn to dusk during breeding season, Lopé’s rain forest echoes with the deep grunts of male mandrills—music, it is thought, to woo the horde’s sexually receptive females while telling other males to take a hike. Augmenting the din are the colors the males display from their tops to, literally, their bottoms.

Flashier than the female, a mature male mandrill has dark red nostrils, snout and brow. His long, white muzzle bears blue stripes that show when he snarls. His genitals range from bright red to pink, and his almost hairless buttocks are iridescent blue. Getting all that neon to glow requires a sturdy heart that pumps loads of blood to the colorful skin. The payoff, as paternity studies have shown, is that males with more testosterone and brighter colors—alpha mandrills—sire more offspring than their low-wattage competitors.

But it takes more than being a primate peacock to win the mating game. Fierce fights break out among breeding males. While the formidable upper canines of a zoo mandrill can grow to two inches long, in the wild those fangs break during mating duels. Of 12 males captured and examined by Abernethy at Lopé, only one had undamaged teeth. Each male also bore wicked-looking scars or fresh rips and punctures on face or body.

Mandrills were long considered close kin of baboons, and it was assumed that—like baboons—they lived in smallish groups consisting of a dominant male and his female harem. Abernethy’s research revealed the startling truth of horde life, that mandrills belong to stable associations of hundreds of other mandrills. The largest horde she recorded numbered an incredible 1,350 animals, although she now believes it was a temporary association of two neighboring hordes.

DNA research has shown that mandrills aren’t baboon relatives—they’re closer kin to drills and mangabeys. And the males—despite their intimidating appearance—don’t run the show. In fact, Abernethy compares mandrill mating rites to those of birds such as sage grouse, in which males dance to attract females. “Males come into the group and display their prowess through vocalizations, color and size. They assess female fertility and try to impose themselves on the most fertile females.” However, females can escape by climbing thin trees inaccessible to the heavier males, so males need female cooperation to mate. “The ‘best’ males will have better success at persuading females to cooperate,” Abernathy says.

So who, if anybody, is in charge of the horde? That remains to be learned. Abernethy says years of mandrill watching have revealed no consistent pattern of leadership. In fact, she says, what fascinates her most about horde life is its apparent “democracy.”

Although Abernethy may not understand mandrill hierarchy, she does know that females in hordes issue what she describes as “shrill wraaaaahh screams,” helping to coordinate group activity even when spread out across hundreds of yards of dense forest. Group vocalization patterns suggest there is increased “discussion” at points where forest paths converge, says Abernethy, “as if many individuals are involved in a consensus decision, rather than a follow-a-leader system.” But no matter how big and noisy a mandrill horde is, if the group detects an apparent threat, members somehow get the signal to switch to complete silence, enabling hundreds of monkeys to noiselessly melt away into the rain forest.

Elusiveness makes mandrills difficult not only to study but to photograph. Working in 2008 in Lopé National Park, Fiona Rogers and fellow photographer Anup Shah created the first extended profile of this unusual monkey. When they began their quest, Rogers and Shah felt they had two things going for them. First, they knew that Lopé’s mandrills stick to the relatively narrow strips of rain forest that follow park rivers; the monkeys rarely set foot in open country where they are vulnerable to predators such as leopards and human hunters. Second, a handful of mandrills were wearing Abernethy’s radio collars, which meant they could be tracked. Nevertheless, weeks passed before the photographers framed a mandrill in their viewfinders.

“First thing in the morning, we’d go to a location where we could pick up the signals from the collars,” says Shah, a veteran wildlife photographer. “Then we’d anticipate where they were going to come to, and we’d build a hide in that part of the forest. But nine times out of ten, we’d be wrong, and the mandrills would go in an entirely different direction.” Almost always moving in search of fruit, seeds and other food, mandrills cover 5 or more miles on a busy day. A missed connection in the morning usually meant another day without mandrills for Rogers and Shah.

When their luck finally turned, the photographers went from dearth to deluge. On one memorable occasion, hundreds of the monkeys swept by the camouflaged blind as the animals crossed a forest clearing. “They came through in streams, four or five abreast in a long line,” Rogers says. Another time, Shah recalls, “tens and tens of mandrills were passing within inches of the hide,” oblivious to the photographers. “That was quite weird.”

Abernethy, too, has found—despite years of observing mandrills—that the monkeys “still do the unexpected on a regular basis.” Her work, she says, “becomes like a game, trying to see if you understand well enough to predict what they’ll do next.” That these colorful and complex monkeys can still confound her only heightens her pleasure in trying to puzzle them out.

Michael Lipske has written for National Wildlife for almost 30 years. Photographers Fiona Rogers and Anup Shah live in Watford, England, and have published articles jointly in Smithsonian and BBC Wildlife. They spent six weeks on location in Gabon’s Lopé National Park, taking about 600 images.

Size Matters

The smallest known monkey is South America’s pygmy marmoset—less than 4 inches long and weighing under 7 ounces. Among all primates, which include monkeys, apes and lemurs, the smallest is the tarsier, a primitive creature from the Philippines that can weigh less than 3 ounces; largest is the mountain gorilla, at up to 450 pounds.

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