Jeffry Oonk and Marleen Azink/Foto Natura
A western lowland gorilla forages in Mbeli Bai, a swampy clearing favored by gorillas because it provides food year-round.
I once attended a slide show on western lowland gorillas. On the screen flashed a slice of Central African rain forest — the dense understory full of thorny stems and ankle-grabbing vines. The speaker informed the audience that there was a silverback, a blackback male, and four female gorillas with their young offspring sitting amidst the vegetation. Most of the audience tried but failed miserably at picking out the 400-pound gorilla with a bright red head and silver back. This, in a nutshell, is the challenge of studying western lowland gorillas in the wild: What constitutes a haven of tasty shoots and young leaves for a gorilla is a veritable botanical torture chamber for a researcher.

Though this subspecies, Gorilla gorilla gorilla, accounts for nearly 90 percent (an estimated 110,000 individuals) of the world’s gorillas, until the discovery of Mbeli Bai in the southwest of Nouabalé-Ndoki in the Republic of Congo, we had been able to observe little of the western lowland’s group dynamics. It was in the early 1990s that J. Michael Fay, a Wildlife Conservation Society (WCS) associate conservationist (see “Walk for Wildlife,” October 2001), made his first visit to the 32-acre Mbeli Bai and opened a window on the society of this elusive ape.

In the local Lingala language, bai denotes a swampy clearing. Often a bai provides a rich feeding patch or a watering hole, as well as a gathering place, for a variety of large mammals. Gorillas come to Mbeli Bai to feed on the large-leafed, protein-packed, aquatic plant Hydrocharis chevalieri that grows in the floating mat of vegetation.

Hauling themselves on two legs through the thick mud, the gorillas wade waist-deep through small streams and rivulets crisscrossing the bai. Some infants clamber onto their mothers’ shoulders; others, hanging on below their parents’ bellies, risk a dunking in the sludge. Groups may spend two to four hours dredging up handfuls of the plant, vigorously washing off excess mud before carefully selecting choice parts to munch from the tangle of roots, stems, and leaves. All the while, they sink deeper into the mud until only their chests and heads are visible. Several gorilla groups may feed at the same time, ignoring one another, save for the odd glance now and then, or peaceably intermingling.

The stability of the rain-forest climate is mainly a myth. In reality, the amount and quality of available food varies considerably throughout the year. At Mbeli, a nutritious meal is guaranteed year-round, which must be what makes it worth plowing through all that muck. The bai’s resources attract other animals as well: forest elephants, forest buffalo, red river hogs, black-and-white colobus monkeys, Congo clawless otters, and sitatunga (an antelope with elongated hooves that splay out across the swamp).

It quickly became apparent to WCS that Mbeli Bai offered a unique opportunity to study gorilla group dynamics. In 1995, Claudia Olejniczak started a long-term monitoring project here, which was carried on by Richard Parnell. In 2001, I took over the project. My predecessors had compiled detailed records on 18 gorilla social groups and eight solitary silverbacks — some 180 individuals. We have given each a name and have named the groups for easier identification.

Western lowland gorillas typically live in groups of several adult females and their offspring of various ages, presided over by one silverback male. Male offspring mature within the group until they begin competing with the silverback for access to the females. He then no longer tolerates their presence, and they are obliged to leave and become solitary. Females transfer between groups for reasons that we have yet to fully understand. As the solitary males develop leadership skills and attract females, they form their own groups.

At Mbeli Bai, field biologists are privileged to participate in a research experience that is totally different from tracking gorillas in a forest. You don’t get the surge of adrenaline that comes from unexpectedly meeting a gorilla head-to-head in thick vegetation. Instead, researchers are perched somewhat voyeuristically atop a 30-foot-high mirador, or viewing platform, at the edge of the bai to collect data and follow what amounts to a gorilla soap opera. These front-row seats offer a panoramic view of the apes, which have become habituated and carry on their business without paying any attention to us.

As we gain an intimate knowledge of the lives of each player, our daily observations provide all the thrills of a serial drama that keeps us in suspense from one day’s episode to the next. What will happen when young silverback Dylan approaches Basil, the silverback of the Noodles group, in a bid for Basil’s females? As if Dylan stands a chance against Basil and his right-hand men, notorious blackbacks Parsley and Bayleaf!

Such research requires patience and time––years, in fact. The drama of birth and of females transferring among groups are rare events. The social development of newly emigrated blackback males does not happen overnight. Each year we piece together a little more of the complex social life of the western lowland gorilla, slowly unraveling riddles whose answers were previously hidden behind a wall of vegetation.

The year 2000 was an exceptional time. Years’ worth of observation were condensed into a brief, six-month period. And it all started with Caravaggio.

The typically aggressive silverback of the Snowflake group had disappeared late in 1999. Apparently in his prime, he may have contracted an illness or, given his short temper, perhaps sustained mortal wounds while interacting with another silverback. The only thing we knew for certain was that Caravaggio was gone. He left behind four females. Two were accompanied by juveniles and one, Salmonberry, had an infant. Basil, the opportunistic silverback of the Noodles group, immediately snatched up two of the adult females, including Salmonberry, for his own group.

During the transfer, Salmonberry lost her infant, possibly at the hands of Basil. Although infanticide has not yet been documented in western lowland gorillas, it is a relatively common behavior in mountain gorillas to halt the gene flow of potential male competitors. The third female, Drift, showed up with Frank, a previously solitary silverback. We had been following Frank’s development from the time he was a blackback in his natal group to his emergence as a newly emigrated solitary male. Now he had become a group leader. Only one of Caravaggio’s females remained unaccounted for; possibly, she had transferred outside of the Mbeli population.

Of course, there is more to Mbeli than its inhabitants’ soap-opera lives. Mbeli Bai is an increasingly rare example of an intact ecosystem. Its gorillas represent an almost completely undisturbed population, giving us the opportunity to collect data on gorilla social behavior under natural conditions. We need this information to be able to predict the effects of hunting, logging, and other disturbances that are occurring to populations elsewhere across the gorilla’s geographical range.

The trade in bushmeat seriously threatens western lowland gorillas. And as logging operations advance, new roads bring in trucks and people, further fragmenting the forest and facilitating the trafficking of bushmeat into towns and cities. Poaching can be devastating to large mammals such as gorillas, species with long gestation periods and protracted infant development. With the effects of Caravaggio’s disappearance on the Snowflake group as an example, we can imagine the repercussions each time poachers remove even a single gorilla from the wild.

The insights we gain at Mbeli Bai will help us devise the best conservation plan. The future of gorillas in Central Africa is uncertain, but we are thankful for this prime vantage point from which we can watch nature’s day-to-day drama unfold.

Emma Stokes, a WCS field biologist, studies the social dynamics and ecology of western lowland gorillas in the Republic of Congo.

http://www.wildlifeconservation.org/feature_story_all_my_gorillas.html