Gabon is also well-known as the long time home of Dr. Albert Schweitzer, the famous physician and humanitarian who in 1913 set up a hospital in Lambarene, Gabon, along the banks of the Ogowe River. Soon after arriving in Gabon, Dr. Schweitzer wrote to a friend: “I am gliding along in a canoe (carved out of a single tree trunk) on the mighty river, which is framed by the jungle, under a blazing sun. How marvelous this landscape is: water, jungle. Nothing, no one. My canoe, with the paddlers singing their ancient melodies, alone on the mighty river, lost in an unknown world. I spot a monkey perched on a huge liana. He sends you his best. Several hours ago I canoed past a half-dozen hippopotami.

Dr. Dixson worries that Gabon’s natural riches won’t last forever. The country is one of Africa’s major oil producers and also has stores of uranium, manganese, gold, and iron. In recent years, logging has increased in the rainforests. “Traditionally, they cut only trees that they could float down the river, but with the advent of a railway, the catchment area for logging has increased, because now they can drag the logs to the railway station,” says Dr. Dixson.

The mandrills, too, are endangered. They have long been hunted as a food source for local people, with little effect on their population size. Now, however, commercial hunters are culling many more animals, sending the meat “down the train line” to coastal hotels. Efforts to protect the wild resources are now starting, sponsored in part by organizations such as the World Wide Fund for Nature.

Walton filmed in Gabon over the course of an entire year, staying in huts or houses, sometimes camping out. “We spent a lot of time going into the forest to find the mandrills,” he says. The troop featured in the film numbers about 80 animals, but Walton also wanted to capture on film the larger troops, which can number as many as 700 animals. “We saw them very briefly, but were never able to film them,” he regrets.

Still, it was all well worth the trouble, says Walton. “Getting that close to a primate that is so secretive and so difficult to film is one of the most amazing experiences, despite the difficulties. At the end of the day, when you’ve filmed these extraordinary creatures, it gives you a sense of wonder about just how many secrets there are out there in the forests and remote areas that we never even think of.

“It really touches you deep down in your soul. You feel that you’ve entered a world that is special. It might sound a bit corny, but it is absolutely true that you feel you have been privileged to see that world. And you do wonder whether something like that will stay the way you’ve seen it. You hope that we as humans will be able to safeguard it in the end. You feel a great responsibility for that.”

Consequently, many aspects of the mandrill’s social organization, mating systems, and other behaviors are still not fully understood. This, says Dr. Dixson, makes the species “the last great mystery among the family of Old World monkeys and apes.” The studies of Dr. Dixson and others are, however, beginning to unravel some of the mysteries.

One of the most fascinating questions is why male mandrills sport such bright colors. As seen in Mask of the Mandrill, Fangs, a dominant male who mates with many females, is much more colorful and larger than other, less successful males. He also has much higher levels of the male hormone testosterone.

“We think we’ve got an alternative reproductive strategy going on here,” explains Dr. Dixson. “The males who are less successful, less dominant, may be going through a period of their lives when they suppress development of the secondary sexual characteristics such as color and size. If they get a chance to become higher in rank, then those features emerge.”

Why do some males hang back? They are essentially conserving their resources. If they are not likely to be able to mate, it doesn’t make sense physiologically to “invest” in reproductive characteristics. A more aggressive male, for example, is more likely to invite aggressive behavior from others, risking injury. There is also some evidence in other species that high testosterone levels can have a detrimental effect on the immune system. Just how the mandrill manages to suppress its development is not yet known.

Another mystery is the purpose of a scent gland found on the chests of mandrills. Males in particular like to embrace a tree and rub up and down against it to deposit scent, says Dr. Dixson. “They all do it, but I haven’t got the faintest idea why. It may be that, given their large home ranges, the males are somehow communicating through these marks.” He suspects they might also use their bright colors for visual forms of communication.

“It is very difficult to see them in the forest, but when you do, the first thing you see is a flash of color through the undergrowth, a flash of nose or rump.” The best way for humans to travel through the dense rainforest, Dr. Dixson says, is to use the paths “bashed down by the forest elephants, but, of course, then you might meet an elephant!”

Frustrated with trying to follow the animals through the rainforest, Dr. Dixson did his research by building an observation tower near where the mandrills regularly gathered to feed. He watched their social interactions for many hours, and also managed to secure blood samples to perform DNA studies and determine the paternity of the offspring. The most colorful, most aggressive males, as he expected, had fathered most of the offspring.

Although they are known for their shyness, mandrills are often called “the devil of the Fang,” a reference to the local Fang people, says Dr. Dixson. “If you see a mandrill in the wild, it’s likely to have a grinning facial expression, with the corners of its mouth open wide and the middle closed, and to be shaking its head from side to side, and showing its enormous canines.” It’s an entirely friendly expression, swears Dr. Dixson, but to our eyes, it seems devilish indeed.

Online content for Mask of the Mandrill was originally posted November 1996.