Solutions
04.17.2024

Subterranean Stronghold

Can Fiji’s first bat reserve keep an incredibly rare species safe despite the growing threats of climate change and human activity?

The first time he stared down the humid mouth of Nakanacagi Cave, on the Fijian island of Vanua Levu, Sanaila Tawake’s hands shook. He’d heard many stories about this place, its entrance half-hidden between mossy limestone boulders in a tract of old-growth dry forest on the island’s mountainous spine. That day, at twelve years old, he’d finally convinced an uncle to take him inside. For the young men of Nakanacagi village—a community of 375 people on red-dirt flatlands about 1.8 miles from the cave—traversing the network of underground canyons was a rite of passage. Tawake had been looking forward to this day for years.

Standing on the threshold, though, he was having second thoughts. “It was so dark, and there were so many different noises coming out,” he remembers: a tapestry of sound woven from the rush of water, the clattering calls of white-rumped swiftlets (Aerodramus spodiopygius) that nest on the cave’s ceiling, and the high-pitched, metallic buzz of bats.

Tawake wasn’t surprised that the cave was so full of life. His relatives often returned from their underground forays with buckets of freshwater prawns and eels they’d fished from the cave’s underground stream. If there was a wedding or another big occasion, they’d even come back with chirping, wriggly sacks stuffed with hundreds of the chocolate-brown creatures they called bekabeka, or “small bats.”

Today, those mouse-sized mammals, known in English as Fijian free-tailed bats (Mops bregullae), no longer feature on celebratory spreads alongside wild pork, cassava, and instant noodles. Instead, they’ve become something of a “poster child” for bat conservation in the Pacific—a region where bats play an outsized role in islands’ terrestrial ecology, but have received little conservation attention until recently. In 2008, the bats were listed as endangered by the International Union for Conservation of Nature (IUCN) because of their limited range and ongoing habitat decline. This cave is the bats’ only known maternity roost in Fiji: a spot where pregnant females gather each year to birth and raise their pups. Since 2018, it’s also been Fiji’s first—and only—bat sanctuary.

Two decades after his first descent into Nakanacagi Cave, the apprehension Tawake once felt staring into the cave’s mouth is long gone. In 2023, he became one of the sanctuary’s first wardens, and he now strides confidently into the underground stream in white gumboots, surefooted on the smooth, slippery limestone. Just inside, he reaches into a crevice and pulls down a floppy-eared, beady-eyed bat, cupping it in his hand to show to a handful of scientists and NGO staff who have come here to help develop Nakanacagi’s first management plan. After a moment, the bat tugs its wings free and flitters away.

Tawake points the red beam of his headlamp upward, revealing a seam of hundreds more glossy bats in the cave’s low ceiling. Their bodies form a close, quivering huddle, their folded wings jutting at odd angles and their tiny claws gripping the rock. In 2011, an estimated 2,000 bats roosted here; at last count in 2018, that number was up to about 7,500, though part of the increase may be due to better technology for counting them. Still, Tawake suspects the number could be even higher now, as he’s seen the animals colonize new spots.

Yet while the new protections the sanctuary provides may further bolster Fijian free-tailed bat populations, the species remains in deep peril. Some 95 percent of all the known Fijian freetails in the entire world live in this one cave. Like many other bat species across the Pacific, climate change and land-use shifts pose big risks to creatures so tied to a single place—and to the villagers who act as their stewards, too. In different ways, both must consider big questions: Is home safe? Should we stay, or should we go?

Bats have a special place in Pacific Islands ecology, as they’re the only native terrestrial mammals in many of the region’s islands and archipelagoes. That makes sense when you look at the vast stretches of ocean separating the more than 25,000 Pacific islands, most of which are so small they’re regularly left off world maps. Few terrestrial animals were capable of reaching these isolated lands until human settlers helped non-native mammals like rats and pigs hitch a ride. Bats—the only mammals that can truly fly—were the exception. Some bat species may have flown across the seas deliberately, while others were flung onto new lands during cyclones.

The unique conditions and isolation of each island prompted bats to evolve in novel ways: Many of the region’s 132 bat species are found in just one or a few locations. Scientists initially classified Fijian freetails as a subspecies of the greater northern free-tailed bat (C. jobensis), which is found in healthy numbers across Northern Australia and parts of Indonesia. But in the early 1990s, Australian mammologist Timothy Fridtjof Flannery set off on a five-year field survey of mammals in the southwest Pacific; when he visited Nakanacagi, he noticed its bats had different-shaped ears than their cousins in Australia. Flannery determined that they were a separate species, with a few counterparts on the neighboring island of Taveuni and a small remnant population (that may yet be another species again) in the nearby nation of Vanuatu.

This specificity and scarcity make Pacific Island bats particularly vulnerable. The region was home to five of the nine bat species that have gone extinct globally in the past 160 years, and a quarter of its surviving species are threatened with extinction. Climate change poses a particular threat to these animals’ highly localized niches. The beka mirimiri, or Fiji flying fox (Mirimiri acrodonta), for instance, lives only in Taveuni’s mountaintop cloud forest, and has been identified by scientists only six times since it was first described in 1976. As warming temperatures shrink that forest—possibly prompting lowland animals to move upward—the species’ ongoing survival looks increasingly precarious.

If more bats disappear, the ripple effects for Pacific Island ecologies and cultures could be significant. As these islands tend to have fewer species overall than mainland habitats, the region’s bats play outsized roles in their ecosystems. Fijian freetails, for instance, eat insects and help to keep in check agricultural pests and mosquito populations—and the diseases and crop failures those insects vector. The nectar-eating Fiji blossom bat (Notopteris macdonaldi), meanwhile, is the only known pollinator for Fiji’s native kuluva (Dillenia biflora) tree, which is used for timber and medicine and provides important habitat for endangered frog species. On a number of Pacific islands, fruit bats pollinate important food crops like bananas, mangoes, and avocados, and disperse tree seeds in rainforests.

But most people in Fiji—and many other parts of the Pacific—aren’t aware that bats contribute to their well-being, says Siteri Tikoca, a Fijian bat ecologist who is completing her PhD on Fijian freetails at the University of Adelaide, Australia. Urban residents largely ignore bats, while in many rural areas they’re seen as either a food source or a threat to crops. Oblivious to bats’ important niche in local ecosystems, people frequently destroy bat habitats and feeding grounds to expand logging and agriculture. “The Lord made these beautiful creatures to play a very important role—and we don’t get that,” Tikoca says. “We don’t connect the dots.”

Fiji's Nakanacagi Cave is the only known habitat where the endangered Fijian free-tailed bat roosts and breeds. Photograph courtesy of Bat Conservation International

Deep inside one of Nakanacagi Cave’s warm, damp caverns, where the light from the entrance is just a dim glow, Tawake points out the rusted remains of a water intake pipe. Farmers had once used the pipe to siphon water to irrigate sugarcane crops, but the residents of Nakancagi Village worried that taking water from the underground stream would harm the eels and prawns they harvested. They would regularly “come and pull the farmers’ pipes out again,” Tawake grinned. The villagers didn’t know it then, but their defiance may have helped keep the bat colony intact: Water extraction can disturb a cave’s delicate hydrology and humidity, and bats are sensitive—they’ve been known to abandon a roost en masse if conditions shift too much.

The feud was about more than water, though. It was also about culture and ownership. Eighty-seven percent of all land in Fiji is categorized as iTaukei (Indigenous land) that cannot be bought or sold; the rest is either state-owned or freehold, the latter of which can be sold outright. In the late 1800s when Fiji was under British rule, the land above the cave was converted from iTaukei to freehold. (No one remembers now if that was the chiefs’ decision or the government’s.) At the same time, tens of thousands of indentured laborers from India were migrating to Fiji to work in the islands’ colonial sugarcane plantations. Some of these Indo-Fijian farmers stayed and established their own farming cooperatives, and two such groups purchased the blocks of land above and around Nakanacagi.

The Indo-Fijian landowners didn’t use the area around the cave much: They owned superior farmland on the flatlands below. But in the 1960s, those landowners had cleared a road that passed just above the cave to access a logging concession higher up the mountainside, and timber-loaded trucks bounced over it, threatening to collapse the cave. The farmers also regularly burned sections of forest and farmland nearby, and occasionally grazed cattle—all activities that could disrupt the cave’s microclimate by affecting the amount of water seeping down to the water table below, or destroy the freetail bats’ feeding grounds.

“There were a lot of threats,” says Jon Flanders, director of endangered species interventions at Bat Conservation International (BCI), a nonprofit based in Texas. “Something [needed] to be done.” In 2013, a consortium of NGOs, led by BCI and NatureFiji-MareqetiViti Fiji, began working with villagers and farmers to protect the bat colony.

They met first with the villagers from Nakanacagi to find out what was locally important about the bats and the cave, share information about the animals’ global significance, and discuss the idea of ending bat harvests for food. The villagers responded much more positively than Flanders had expected. “We kind of just presented the information, and they really took over (as) the custodians of that cave and of those bats,” says Flanders. “They didn’t realize how endangered they were, and they were the ones who chose not to harvest bats anymore. They suggested that to us, and we were like, well yeah, that would be great.”

It proved more challenging to persuade the Indo-Fijian farmer-landowners to stop using the logging road and water intake pipe. So in 2016, the consortium began working on a more ambitious plan: to buy the land above and around the cave outright. “I think realistically that was the only way of mitigating the [threat from the] logging roads,” says Flanders.

The group pulled in funding and logistical support from the National Trust of Fiji, a government conservation body, and international nonprofit Rainforest Trust, and began to negotiate. Two years—and plenty of cups of tea and coconut shells of yaqona (kava)—later, the farmers agreed to sell 55 acres of land to the National Trust. Together with the underground cave, it was designated as the Nakanacagi Bat Sanctuary. It was a win-win: The farmers got money for land they were hardly using, and the bats and other cave species gained another layer of security.

For Nakanacagi’s villagers, the sanctuary is a boon both symbolically and practically. They’re still allowed to harvest eels and prawns there, and the new protections make it more likely that those species will continue to thrive. And although the cave is now technically government-owned, “it feels like it’s back with us now,” said Tawake. He and other villagers earn income from their work monitoring biodiversity in and around the cave, checking for illegal activities such as bat harvesting and deforestation, guiding researchers inside the cave complex, and educating young people about the sanctuary’s importance.

But soon after the bats’ roost was secured, something happened to make both the sanctuary and many of the villagers’ own homes feel much less safe.

“This place, where you see that [papaya] tree, there used to be a house,” Tawake tells Nathan Breece, an assistant director at BCI who is part of the team creating the sanctuary’s new management plan.

The two men are standing in a scrubby field of knee-high grass among plots of taro and cassava. Four splintered foundation posts are the only evidence that this was recently somebody’s home. About 65 feet from the posts, the land abruptly subsides and two wide, brown rivers pour together to form the thicker braid of the Dreketi River. The Dreketi is the deepest river in the country, draining into the sea through a mangrove-covered delta about 9 miles downstream. At high tide, warm, salty seawater rushes back up past Nakanacagi Village, and local fishers catch sharks and other sea creatures that have been swept up in the current.

This hydrology became especially relevant in 2020, when a Category 5 storm nicknamed Cyclone Harold made landfall on Vanua Levu. On the evening of April 7, as gale-force winds smashed windows and whipped off roofs, Nakanacagi’s chief blew his conch: a signal for everyone to evacuate into the community hall for the night. His call was well timed. Early the next morning, a high tide collided with the floods hurtling downriver, and muddy water burst over the banks, ruining crops, sweeping away several homes, and submerging others so deeply that only their roofs protruded above the waterline.

Tikoca, the Fijian bat ecologist, was in Adelaide at the time and recalls desperately trying to make contact with people in Nakanacagi. “When I finally got through to them and asked what they needed in terms of support, and they said they needed food, I realized just how dire the situation was,” she says. Tikoca and her colleagues put their bat research on hold and raised money so the villagers could buy emergency supplies: packs of crackers, tins of tuna, boxes of nails, and stacks of corrugated roofing iron. “Helping them is helping the bats,” she says. “It isn’t two separate issues.”

Although climate change poses dangers to human and wildlife populations around the world, Pacific Islands are particularly vulnerable. Tropical storms and cyclones appear to be growing more intense and destructive as the climate warms, and sea levels around the islands are rising. As extreme weather events become more frequent in Fiji, environmental threats also dangle over the free-tailed bats’ future. Drought could dry up the stream and alter the cave’s humidity beyond what the bats can tolerate. Wildfire is also a serious concern; if the forest above the cave burned and it later rained heavily, there would be no vegetation to absorb the runoff, and rainwater would hurtle through the cave with likely “devastating consequences,” says Breece.

At a workshop to develop Nakanacagi’s management plan, groups of villagers circled around reams of paper to sketch out the most likely threats and brainstorm ways to mitigate them, such as fencing to prevent grazing in the surrounding forests, reforestation, and using machetes to clear nearby tracts instead of burning. As they formalize the plan over the next few months, they’ll decide which of these methods to take on as a community.

While the villagers’ sense of ownership and responsibility was apparent, the exercise also showed the limits of their power to protect the sanctuary—especially because the underground stream the bats rely on is fed by a watershed that stretches beyond the boundaries of the protected area. Since the sanctuary’s formation, the consortium has been trying to make sure water and land use in this wider watershed doesn’t harm the cave’s delicate ecosystem. But the quest is complex because there are lots of landowners—and some lucrative logging and farming opportunities—within the watershed.

On neighboring Taveuni Island, 70 miles away from Nakancagi, bat advocates are on a more basic—but equally confounding—quest: to understand the bats of Taveuni and their relationship to the Nakanacagi bats. Tikoca has been catching freetails in Nakanacagi and on Taveuni, taking tissue samples from their wings, and genetically analyzing them to find out whether the freetails on Taveuni were born in Nakanacagi, or whether it’s a different population—or even a different species—entirely. Protecting the Taveuni population could increase the odds of the species’ survival on both islands.

Tikoca says it’s not out of the question that the bats could be flying from Nakancagi to Taveuni (with some stops along the way) and returning each year to birth their babies: Freetails can fly about 37 miles in one night. But her work so far suggests that’s unlikely. “There seems to be limited gene flow between the two islands,” she says, meaning there’s probably at least one maternity cave on Taveuni, too.

“The question is, ‘where?’” asks Sipiriano Qeteqete, the coordinator for Taveuni’s Bouma National Heritage Park, which stretches from the island’s cloud-forested crater down steep ravines to the pandanus-and-coconut-studded coastline below. From his home in nearby Lavena Village, Qeteqete often spots freetails flying out of the park at dusk and buzzing around the villagers’ dim solar-powered porch lights to eat insects.

Qeteqete has been on several expeditions with Tikoca and others to try to find where the bats might be roosting, but the terrain is too vast and rugged to explore systematically. He thinks the most promising solution is to recruit locals who have the bush skills and fitness to handle it—maybe the village’s young pig-hunters, who regularly disappear into the hills at dawn and return in the evening with (non-native) wild boars slung over their shoulders.

“They are the ones that know how to go from here to there, and this side to that side,” he says. “If we give them an extra bonus so they can do that work while hunting at the same time, they can cover the whole interior…. Otherwise, I think we can forget about finding the cave.”

It seems such a low-cost—and potentially high-impact—approach to finding and safeguarding the freetails’ last unprotected population. But Tikoca says that cash for environmental initiatives in Fiji is difficult to come by. In particular, “getting money for species conservation is really hard,” she says.

Funding to help Fiji’s human communities survive the threats posed by a changing climate is equally scarce. No one in Nakanacagi was injured after Cyclone Harold ravaged the village, but many villagers lost their crops and homes. Without government assistance available to recover from the cyclone, the village had to take on the initiative on its own to relocate people from flood-prone areas and rebuild on a ridge farther from the river, Tawake says. Villagers have already erected three houses there, and pineapples and cassavas line the newly scraped road.

 

Residents of Fiji's Vanua Levu are moving their homes to higher elevations to escape storm surges and the various climate change factors that are driving these threats. Photograph by Monica Evans

While Nakanacagi’s villagers can move to safer locations, it’s unclear whether its bats can do the same. What is clear is that the fate of Vanua Levu’s rural communities and its bats are deeply intertwined. Securing the well-being of the island’s human residents may also improve the bats’ chance of remaining in their home; protecting bat populations might similarly protect human communities from insects that carry disease or eat crops.

In the evening in Nakanacagi, you can see the bats chase those insects in the violet dusk. It’s rush hour: Swiftlets dart inside to sleep as the bats whoosh out to hunt for prey above the canopy. The sky is alive with wings and sounds. In the morning, villagers in Nakanacagi will again get up early to pry boards from homes drowned by the flood and lug them to building sites up the hill. The Fijian freetails, full-bellied, will return to their cozy upside-down roost in the rock. For now, both humans and bats have their place.

Monica Evans

Monica Evans

Monica Evans is a nature writer living in a small town called Raglan on the west coast of Aotearoa New Zealand. She writes regularly for international publications such as Mongabay and Hakai Magazine. You can see more of her work at monicaevans.org.

Christy Frank

German-Australian marine and nature photographer Jürgen Freund uses his skills from his training as an engineer to create special lenses and underwater gadgets making his photography innovative and unique. His photographs are used extensively by conservation agencies like WWF and Conservation International, and he has authored several WWF coffee table books namely The Coral Triangle and the Sulu Sulawesi Seas. He currently lives in Far North Queensland, Australia, and considers the entire Australian continent as his photographic studio.

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