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.”