Big on Figs

In Indonesia, one nutritious fruit is the wild fuel that runs the rain forest

• Margaret Kinnaird
• Jan 01, 2000

The sun has barely risen over the sea, but its hot rays are already bathing the steamy forests of Tangkoko Nature Reserve on Sulawesi Island in Indonesia. The morning is heralded by a cacophony of wild calls and screeches in the forest canopy above me. It seems every animal in this small reserve is converging on an enormous fig tree. I have been watching this tree for weeks, and now its entire burden of fruit­­ - between 400,000 and 600,000 figs - ­­is ripening all at once. The bounty attracts birds and mammals from all directions to partake in a feeding frenzy.


But why, in a forest that harbors hundreds of different types of fruiting trees, is this fig so irresistible to so many forest creatures? This is the question I came here to answer.

I have been fascinated with figs ever since my first encounter with them as a five-year-old dissecting Fig Newtons in my parents´ Kentucky kitchen. Back then I was delighted with the flavor of the gooey paste squeezed between soft pastry and intrigued by tiny seeds that peppered the dark brown fillings. Now, some three decades later, I´m still captivated by figs, but this time as an ecologist with the Wildlife Conservation Society, studying the role of figs in rain forest ecosystems.

I knew that if I could figure out why figs are irresistible to the denizens of Sulawesi´s forests, I could shed some light on why so many other tropical animals around the globe also relish them. Figs are consumed by everything from tiny ants to 2-ton elephants. Our closest relatives, chimpanzees, crave them. Even a bear cuscus, a woolly marsupial found in Sulawesi´s forests and normally a leaf-eater, won´t turn down a succulent fig.

I wondered if this wide appeal is simply due to the abundance and diversity of fig trees. There are more than 600 species of figs in the Tropics, making them the second-largest group of woody plants in the world. Many of these are in the Indo-Malay region. Sulawesi (also known as Celebes), an island in the middle of the Indonesian archipelago, alone boasts more than 100 species. The island´s figs grow in locations as diverse as rocky shores, mountain tops and even the cracks in older buildings in the provincial capital of Manado.

Tangkoko Nature Reserve is the perfect place to study figs. In my 1,000-acre research area, there are about 37 species of fig trees with a density of about 5 trees per acre­­the highest fig density recorded in a Southeast Asian forest. Despite the profusion, it´s not difficult to tell the figs apart. Some species look like a typical tree, with a single trunk growing from earthbound roots. Others, known as strangling figs, look more like a confusing maze of roots and tendrils than a real tree.

The fruits span the spectrum from creamy white to blue black, and range in size from tiny pearls to golf balls. (Technically, these aren´t really fruits, but a collection of inverted flowers surrounded by a fleshy, bulbous structure with a tiny hole in the end.) Some sit on thin pedestals or dangle from the tips of twigs; others perch directly on branches, lined up like kernels on a corncob. Some even droop from branches in graceful clusters stretching more than 2 yards. My favorites protrude like cauliflower heads directly from trunks.


Strangling figs are the most abundant fig trees in Tangkoko and the easiest to differentiate from other trees. They have an upside-down approach to life, beginning as seeds deposited high in the canopy by a bird or monkey. The seeds germinate in nooks and crannies of other trees and send delicate root tendrils downward. Once the roots reach the ground, they develop into woody, ropelike structures that begin to surround the host, and slowly fuse and harden. As a strangling fig grows, it takes on the appearance of a coil of ropes, binding its host in a tight, and sometimes deadly, embrace. The host tree´s bark is often crushed and critical fluid supplies are cut off by the fig´s deadly hug. In time, some figs­­like the one I´m standing under­­become free-standing trees with an internal framework mirroring the form of the long-dead host.

Above my head the noise level escalates to that of a New York City intersection at rush hour. Scores of sleek, black mynas, an assortment of tubby, green fruit pigeons, a few tiny parrots hanging upside-down and a legion of stately red-knobbed hornbills pummel me with discarded bits of cherry red figs.

While these raucous animals busily gulp down the fruits, I begin my day´s work. Scanning the tree´s half acre of branches with my binoculars, I estimate about half the fruits are still green­­ - so the site promises to be even more chaotic in a few days when the entire canopy is ripe. I troop on to investigate the fruiting status of the other 155 fig trees that are part of my regular monthly round.

From my studies, I know that the presentation, color and size of fig fruits influence which animals feed on what, and when. Fruits displayed on the tips of branches are available primarily to small birds­­ - the flowerpeckers, mynas and delicate, hovering sunbirds that can feed on the wing. Heavy-bodied hornbills and monkeys can only feed on these figs if they can reach them from a safe seat in the canopy. Figs that grow on trunks tend to be snatched by large, dog-faced fruit bats that might have trouble negotiating the web of branches and twigs in the canopy. Fruits close to the ground are gobbled by babirusas (forest pigs), deer and other earth-bound animals.

Color seems to provide important clues to the ripeness of the fruit. I often see Sulawesi red-knobbed hornbills cocking their heads from side to side while scrutinizing a light orange fig, then hopping to another branch to select a deep red one. I also see hornbills pass up small-fruited figs that would draw doves and pigeons in by the hundreds. Because hornbills pluck fruits then toss their heads back to swallow each morsel, feeding can be time-consuming for small rewards­­ - especially since the birds´ aim is not always exact and they tend to drop the fruits. Big figs don´t seem to pose an obstacle to any animals - ­­the fruits are so soft that even the golf-ball-sized figs can be pecked, ripped and torn by small creatures.

As I approach my next fig tree, I recognize Rambo, the name that my coworkers and I have given to a group of Sulawesi crested black macaques that we have followed for several years. Three jet black juveniles are dangling by their back legs, their long top-knots falling forward as they reach to snap off branches laden with light pink figs the size of small beads.

One monkey swings back into sitting position, the ends of the branch grasped in both hands, and begins to gnaw on it like someone enjoying corn on the cob at a Sunday picnic. Stopwatch in hand, I count the number of fruits he gobbles down - ­­he clocks in at a record 140 fruits per minute! Meanwhile, several satiated females descend the tangled network of roots on this strangling fig and find a cozy spot to nap.
 
From my research in Tangkoko, I´ve learned how important figs are to Indonesia´s wildlife. It rarely takes the monkeys more than two days before they locate a fruiting fig. Then, if the tree is big enough and full of ripe snacks, the monkeys spend hours in its boughs. They casually munch fruits, stop to groom and nap, then wake and resume feeding. On average, about 20 percent of the monkeys´ diet is made up of figs. Red-knobbed hornbills are even more hooked on figs than macaques. Figs make up 85 percent of the fruits delivered by males to nesting females and chicks. To these animals, fig trees are like the McDonalds of the forest­­one on every corner and always open.

Other researchers have speculated that figs are important to rain forest animals because the trees tend to produce bountiful crops that ripen quickly, creating one- to two-week fruit bonanzas. Figs also tend to be available when there is little else to eat. This is because fig trees - ­­even those belonging to the same species­­ - follow individual schedules and rarely fruit at the same time. Unlike mangoes and other tropical fruits, a diverse community of fig trees provides food year-round.

But the volume of figs offered every month of the year did not explain why they were so highly preferred over other foods. Even when other trees provided temporary eating opportunities, Tangkoko´s fruit-loving birds and mammals still targeted figs. Perhaps figs contained some important nutrient? I knew from prior work in East Africa that figs are packed with carbohydrates, a major source of energy. But no one had looked into their nutritional value. So I contacted Ellen Dierenfeld, an expert in animal nutrition at the Bronx Zoo, and asked her for help. She agreed to analyze the nutritional and mineral content of Tangkoko´s fig and non-fig fruits. My task was to collect every fruit I could get my hands on.


For more than a year I gathered figs­­ - mostly those that had been dropped to the ground by messy birds and macaques. But sometimes I was forced to steel my nerves and climb into the canopy for a sample. As I searched under one fig that was bearing a full load and found no fruits on the ground, I realized that I´d have to climb.

I slipped between two telephone-pole-sized roots and entered a hollow chamber created by a long-lost host. The latticework formed by the strangler´s interweaving trunks provided a perfect ladder and I scurried up 130 feet to the top. From this lofty perch, I peered out at the patchwork of green treetops that blankets the slopes of Mt. Tangkoko and ends about a mile to the north in the sparkling Sulawesi Sea. Locking my feet between the roots and bracing my knees against a horizontal branch, I cautiously reached out, plucked 10 ripe figs and dropped them into plastic film canisters.

As I lingered in the cool breezes of the rain forest canopy, a slight movement in the shadows caught my eyes. Suddenly I realized I was staring into the gremlinlike face of a spectral tarsier. These primates are no bigger than a coffee mug but their enormous eyes, sensitive ears, large teeth and rotating heads create a devilish image that more than makes up for their small size.

Tarsiers don´t feed on figs, but the trees still play a crucial role in their lives, serving as bedrooms. Nearly every big strangler in Tangkoko is occupied by a family of tarsiers. The primates sleep in the branches by day and descend to the lower canopy to hunt insects by night. Mates give eerie, ear-piercing calls as they return to tuck into bed, and these demonic cries are, in part, why local villagers believe fig trees are haunted.

I descended the tree, my collection of fruits now complete. I sealed the various bottles, vials and canisters full of preserved figs and then shipped them off to the Bronx Zoo. Several months later, I received word that an important fax from Dr. Dierenfeld was waiting for me in Manado. I hopped into my battered Land Cruiser and began the four-hour journey around the mountain and across the tip of Sulawesi´s northern peninsula to the city.

The results were in­­ - and brought some surprises. Our tests revealed that figs are an important natural source of calcium, critical for strong bones and eggshells, blood clotting and numerous cell functions. Figs have, on average, nearly three times more calcium than nonfig fruits and contain calcium levels higher than minimum dietary requirements for growing primates. Several fig species contain enough calcium to support a hen laying 300 eggs a year. The results were so exciting that Ellen tested fruits from South America and Africa and found that Tangkoko was not unique­­ - the pattern held around the world.

At last, we had found the answer to the question that brought me to Tangkoko. I now knew that figs are irresistible to so many forest denizens not only because they are plentiful and provide enormous quantities of food year-round, but because these succulent fruits in all their various sizes, shapes and colors provide an essential nutrient.

On my way home I mused about how figs benefit from their relationship with fruit-eating birds and mammals, since few associations in nature are one-way. Fig-eating animals get a nutritious treat and, in return, figs get free transport for their seeds­­ - complete with fertilizer. I imagined the millions of fig seeds dispersed through the forest by big-tusked babirusas or dropped from the canopy by far-ranging hornbills and macaques.

In the larger scheme of things, fig-eating animals drive the cycle of rain forest regeneration, and even help construct all those beds for tarsiers. The web of interdependency in the forest, I realized, is as intricate as the roots of a strangler fig.

Margaret Kinnaird is a biologist with the Wildlife Conservation Society. She lives in the Indonesian rain forest with her husband, biologist Tim O´Brien. Roving editor Tui De Roy and her partner, Mark Jones, spent two months with the author climbing fig trees and photographing the wildlife that depends on their fruit.

Of Wasps and Figs 
One of the smallest rain forest residents to use the fig may actually be the most important. Tiny fig wasps spend most of their lives inside fig fruits and are solely responsible for fig pollination. The saga begins as female wasps wriggle into an unripe fig through a small hole at the end and lay eggs in developing flowers inside. As the females search for egg sites, they pollinate the flowers with pollen carried from the fig where they were born. Mission complete, the females die. Their young hatch just as the fleshy part of the fig begins to ripen. Within hours of hatching, mating begins. Then males bore out of the fig, only to die shortly thereafter. Females then exit and disperse, sometimes as far as 7 miles, to find another fruiting fig where they repeat the cycle.