The Kingdom of Rarities (22 page)

The sheer size of the latrines and the dense stands of
Trewia
trees they supported were a revelation of sorts. So was a paper I had read prior to coming to Nepal, which presented a controversial hypothesis formulated by Dan Janzen, one of ecology's leading thinkers, and Paul Martin, a world-renowned paleontologist. They dubbed their idea “the megafaunal fruit syndrome,” and we speculated that it might explain the phenomenon of latrine groves. Janzen and Martin proposed that the now extinct New World tropical megafauna—ground sloths, elephant-like creatures, prehistoric horses, and other giants of the Pleistocene—once played a major role in the dispersal of the woody flora. They argued that the long coexistence of neotropical plants and large mammals that ate large fruits influenced the evolution of fruit and seed traits of some plants so they would be consumed and dispersed by giant mammals.

What is a megafaunal fruit? The short answer: picture an avocado or a mango. In theory, such a fruit would be eaten by big mammals with large mouthparts that could easily handle fruits too big to swallow and too hard for smaller contemporary fruit eaters—birds, bats, rodents, monkeys—to crack open. The classic example is a dull-colored large fruit that shields its big seeds in a thick shell or rind that is hard when the fruit is ripe. Presumably, coevolution occurred because giant mammals provided a better vehicle for dispersing the seeds of these plants than did small fruit eaters or gravity alone. Those plants that created fruits with features attractive to big mammals received more attention and better dispersal to safe germination sites. The mammals received a highly nutritious and concentrated meal from the pulp surrounding the seeds, which they digested before passing most of the seeds intact. Such efficiency in feeding for the big mammals and distant dispersal away from the parent tree helped to cement this relationship—an evolutionary pas de deux—between two seemingly unlikely partners. For the rhinos of Chitwan,
Trewia
fruit fit the bill as a megafaunal fruit.
Trewia
is the most common tree in the forests bordering the Rapti River, but no arboreal or flying creature touched its ripe offerings. Instead, these large green fruits, about the texture and size of young apples, carpeted the forest floor, and the rhinos vacuumed them up.

To test the hypothesis that the dominant plants that had evolved in Chitwan were those not only eaten but also dispersed by megaherbivores, I had to look at the situation with and without the big wild mammals to assess the strength of this interaction. In the absence of rhinos, cattle, deer, or water buffalo—the large fruit eaters—uneaten fruits pile up and rot, their seeds are attacked by bright red insect seed predators called largid bugs, and there is almost no germination. But what we had documented so far was the importance of large herbivores to fruit removal. We didn't know anything about seed dispersal.

To find answers, we needed a volunteer rhino to observe. Sunder Shrestha offered us Kali, the one-horned rhino at the National Zoo in Kathmandu. We drove up to Kathmandu on several occasions to conduct feeding trials. Kali was a willing participant, even though she had probably never tasted a
Trewia
fruit because she had been taken to Kathmandu as a calf. The fruits were placed on a ledge in her enclosure so she could accept or reject them. During the first trial, using her prehensile upper lip as a rake, she ingested all 114 of the fruits placed in front of her in 10 minutes. On a second trial a few weeks later, she ate 300 fruits in 50 minutes. Each time, we waited for the seeds to come out the other end.

Kali let us collect her dung each day, and Vishnu, Kancha Lama, and I painstakingly picked through hundreds and hundreds of kilograms of bright green rhino dung to extract the shiny black
Trewia
seeds. The first seeds appeared within 46 hours after ingestion, and the peak occurred between 60 and 84 hours after Kali ate them. The last whole seed to emerge took its grand time, appearing 172 hours after intake. Because we knew there are approximately 3.2 seeds per
Trewia
fruit, we estimated that about 60 percent of seeds ingested made it through Kali in the two feeding trials.

Being eaten by a rhino, then, was not a dead end for
Trewia
seeds, which is a good thing, given that during the fruiting season as much as 10 percent of the rhino's diet can be
Trewia
fruit. It also gave the seeds a brighter future. It turned out that gut treatment and manuring of seeds had no effect on seed germination. But being encased in giant pillows of dung gave young seedlings a huge boost over seeds planted in soil.

And where rhinos defecate really matters. Like the rain forest tree seedlings in the Peruvian Amazon,
Trewia
sprouts do poorly under the parent tree in the dense forest; they belong to the caste of seedlings that biologists call shade intolerant. To prosper, they need to be manured into grasslands exposed to intense sunlight. By planting seeds and seedlings under various conditions and moving latrines from shade to sun and vice versa, we were able to establish that rhinos are essential to the survival of
Trewia
. Clearly, the latrines were a significant phenomenon, not only as a landscape feature but also as a beachhead for woody plants in a sea of grass.

Giant herbivores shape their world in other ways as well. In the winter months, the rhinos in Chitwan, for example, shifted from grazing grasses to browsing tender shoots and leaves in the riparian forest next to the wild cane. During December, the sound of rhinos walking over saplings of wild avocado trees filled the damp night air. By the end of February, when the rhinos switched back to grazing, the riverine forest resembled a war zone of flattened wild avocado trees. Yet rather than dying off, the trees adapted to this abuse. They grew horizontally and sent out new shoots snaking in all directions, like a woody medusa.

What might a rhino-less forest look like? Given the decline of rhinos in so many places, this wasn't an idle question. We constructed stockades sturdy enough to exclude rhinos. After three years of protection, we compared tree growth inside the stockades with that in paired plots where rhinos had enjoyed free access. The results were striking, even to the uneducated eye. Where the wild avocados were protected, their stems grew straight to the sky;
where rhinos worked them over, trees remained stunted. Rhinos do the same to wild rosewood and a tree genus called
Mallotus
. In a similar way, elephants suppress silk cotton trees, Asia's analogue of the baobab. If left unattended in a silk cotton grove, elephants will girdle the trees to reach the tasty inner bark and kill them, rapidly converting a silk cotton tree savanna to a grassland.

So, in a forest still stocked by its Pleistocene herbivores, only the saplings that are unpalatable to the giant browsers will ever reach the canopy. For the invertebrate species, such as sucking bugs and beetles, that can eat the trees unpalatable to the large mammals, the more favorable ratio is a blessing. For other browsing herbivores that eat the same plants as rhinos do, the trampling behavior of the pachyderms leaves more browse potentially available in the layer they can reach. In short, an Asian forest minus rhinos and elephants will barely resemble one where they are the dominant browsers. Once-in-a-century monsoon deluges may reset the ecological clock on the floodplain. But between the flood events, it is truly the big beasts, through their manuring of seeds and intense pruning, that influence the structure and composition of the riverine forests and savannas.

Beyond Asia and its rhinos, rare vertebrates serving as ecosystem engineers are evident in many environments. Besides the fruiteating birds of paradise in New Guinea and hornbills in Asia, the large frugivorous birds in Amazonian forests and fruit-eating monkeys have an important impact, as we saw in Peru. In the habitat of the Kirtland's warbler, beavers, even at low abundance, create habitat with their damming of streams. Studies suggest that prehistoric mammals, such as woolly rhinos, created the productive Pleistocene high-latitude steppe through their intense grazing and trampling, just as the greater one-horned rhino and white rhino maintain what one biologist has termed “grazing lawns,” where the close cropping of grassy areas by giant herbivores with prehensile lips keeps a low sward at a height that benefits many smaller herbivores in their search for nutritious grasses. In the boreal forest zone,
the giant today is the moose, but this browser eats mostly twigs. How different would the boreal forests look if they still had their full complement of mammoths and rhinos?

Although rhino numbers were increasing in Chitwan while we were there, Hemanta Mishra knew that an epidemic, a severe outbreak of poaching, or a catastrophic flood could decimate Nepal's only population. In the 1980s, translocations of endangered rare mammals to reestablish extirpated populations had become a centerpiece of conservation efforts around the globe. The more populations were spread across their historical range, the theory goes, the greater was the likelihood for the species to adapt to new or changing conditions. Creating a second and even a third rhino population within their former range could be an important hedge against local extinction. As a rule of thumb, conservation biologists advocate that at least ten populations of an endangered mammal species be established initially, with at least 100 founders in each, to reduce the threat of extinction. More than two hundred years ago, rhinos roamed across the Bardia and Suklaphanta reserves in the far western part of Nepal's Terai lowlands. Now these areas were well protected and ready to accommodate their former residents.

So, in the early evening of a winter night in 1986, I found myself riding shotgun in one of three timber lorries the government had provided for transport. The payloads were three tranquilized but awake rhinos housed in giant wooden crates. Captured earlier in the day, they were bound for Bardia, 250 kilometers to the west. Under the full moon, our caravan rumbled cautiously along the winding roads of southern Nepal. I sat in the cab listening to Vishnu's stories, which took my mind off how risky this venture seemed every time our rhino passenger shifted in her crate.

After fifteen hours, one flat tire, and one truck temporarily stuck in a river, we made it to the release site in Royal Bardia National Park. By now, Vishnu and his team had perfected the capture-and-release
protocol. The door of the first crate was opened, and out rushed the first female rhino. The next animal to be released, a subadult male, burst out looking for something in his path to crush. The last rhino to be unleashed also seemed ready to charge but changed her mind and walked into the tall grass.

Ironically, attempts to translocate and recover some of the mammals smaller than rhinos proved much more difficult. Blackbucks—a beautiful antelope species—moved from a wild animal park setting into protected areas thrived at first but then disappeared if the grass grew too tall and gave cover to hunting tigers. The smaller, more highly strung deer and antelope also had high mortality during capture and translocation. No one could capture bristly rabbits. Although pygmy hogs have recently been captive bred and released back into the wild in India to create new populations, captive breeding of musk deer had stalled because of significant mortality during the process. For some reason, the greater one-horned rhinos responded beautifully to the morphine derivative used to sedate them. Could this be one more aspect of their rugged nature? Perhaps those same selection pressures for resistance and resilience made them, however inadvertently, easier subjects to ship out for restoration.

Those first three translocated rhinos were eventually joined by ten others. In late December, seven days after starting the capture operation, we left Bardia, having deposited the last of the group of thirteen. When we captured the rhinos for this translocation, I had touched the horns of each. I wondered how the fate of the five rhino species might have differed had they never evolved facial horns. Would their size and habitat specialization still have rendered them so endangered? The absence of a horn, or even the drastic measure of dehorning rhinos—tried in Namibia and Zimbabwe to deter poachers—would have little effect on a major threat to their survival posed by habitat loss, as is the case today. On the way back to Chitwan, we drove through one poor mud-walled village after another. The rice harvest had just been taken in, and
stacks of straw lined the way. In this region, with one of the world's highest birthrates, pressures on land and critical rhino habitat could only escalate.

We pulled up to a teahouse not far from Lumbini. The stall was swarming with flies, thousands upon thousands of them, coating the hanging sweets and landing on the rims of the unwashed teacups. My desire for a snack quickly diminished. The Zen phrase “Where there are men, there are flies, and also Buddhas” came to mind. In truth, we were near the birthplace of Gautama Buddha, who as young King Siddhartha gave up his royal life to wander as a peasant and find enlightenment. Lumbini has become an international draw for devout Buddhists. Just as Nepal's religious shrines draw wide support and popular praise, I thought, so should its miraculous recovery of endangered wildlife, against all odds, in one of the poorest nations on Earth. I left my daydream as Vishnu gestured to me. The ever-efficient tracker had located a cleaner tea stall, and we sat down for a refresher.