Media & Education
BATS Magazine

Volume 39, Issue 1, 2020

The Pride of Tan Lap



With a lot of shoe leather and a bit of fencing, a scientist turns the tide for Vietnam’s largest bat colony

Decades ago, the villagers of Tan Lap in Vietnam would descend to the cave in the forest adjacent to their homes, drawn by its natural riches, namely, the abundance of bats that made the cave home.

While the guano deposits were valuable enough—for fertilizing the villagers’ own fields, as well as to sell to neighbors—the bats themselves were the main draw. Bat meat, according to local tradition, made a body strong. So, with hand nets and small snares hung from tree branches near the cave’s mouth, the villagers took advantage of a seemingly endless source of protein.
Mammalogist and bat researcher Dr. Vu Dinh Thong, with the Vietnam Academy of Science and Technology in Hanoi, first came to Tan Lap in 2011 to conduct species identifications at the request of a colleague studying zoonotic diseases and interactions between bats and humans. But when he arrived at Tan Lap, what he found wasn’t just a sizeable colony of wrinkle-lipped free-tailed bats (Tadarida plicata)—it was the largest colony he’d ever seen anywhere in the country, perhaps in the entire region.

“It’s a very special cave, not only for Vietnam, but for all of Southeast Asia,” Dr. Thong says. It is one of only five caves of such size anywhere in Vietnam, Myanmar, Thailand or Malaysia, in terms of both sheer space as well as the number of bats it is able to accommodate. Like Bracken Cave in Texas, where the nightly exodus of Mexican free-tailed bats takes hours, millions of wrinkle-lipped bats roost in Tan Lap Cave, according to Dr. Thong.

But by the time Dr. Thong visited the cave, the locals had leveled up their bat-trapping tactics. By stringing large fishing nets across the entrance of the cave, they were able to catch many more animals in a single night. Combined with regular disturbance of the cave for guano collection and general curiosity, Dr. Thong knew that even as large as it was, the colony of wrinkle-lipped bats could only absorb the impact for so long before suffering a collapse.

That realization spurred Dr. Thong, who at the time was one of only a handful of bat specialists in all of Vietnam, to set out on a campaign to protect the bats of Tan Lap Cave. He began talking to the locals about the importance of the cave and its bats, but he encountered resistance.
“Many old people didn’t understand my message that the bats could disappear in the near future,” Dr. Thong says. “They’d been hunting there for many years, and at the beginning, it wasn’t easy to convince them.”

In 2012, with the help of a $5,000 emergency conservation grant from BCI, Dr. Thong began to patiently and repeatedly reach out to as many people as possible about the importance of the cave and its colony. He explained the level of hunting going on at the cave far exceeded what had been done in the past. He raised the idea of the colony one day being a possible draw for ecotourism—if it survived.

Ultimately, he appealed to the farming community where it really mattered: their crops. The bats, he explained, were more than likely providing a massive pest-control service in the farmers’ rice fields, reducing damage and improving yields.

A 2014 study from Thailand showed wrinkle-lipped bats alone prevent the loss of 2,900 tons of rice per year. That volume represents a pest-control savings of $1.2 million annually, or meals for an estimated 26,200 people every year. And because the Tan Lap bats only spend about half their year in the cave—Dr. Thong suspects they may spend the balance of the year in Myanmar or northern Thailand—the colony very likely provides similar ecological services for other areas in Southeast Asia.

“They began to understand how important their bats were,” Dr. Thong says. “And that it could also be a problem for people in other countries.”

The owners of the land where the cave is located were more than happy to collaborate, even going so far as to put up a small guard shack near the entrance of the cave where family members would spend the night. Simply having people present nearby seemed to deter hunters and keep intruders off the property. But someone couldn’t be there all the time, and the harvests continued. A physical barrier of some kind at the mouth of the cave would be required, Dr. Thong concluded, and more work in the community was clearly needed.

This year, with the help and blessing of the cave’s owner and the regional natural resources authorities, Dr. Thong coordinated the construction of a simple fence at the mouth of Tan Lap Cave. Difficult but not impossible for hunters to climb over, the fence has drastically reduced hunting in the cave. Combined with the landowner’s ongoing night watches, “the bat colony is very well protected now,” Dr. Thong says.

Though the BCI grant enabled Dr. Thong to undertake several rapid species and habitat assessments at Tan Lap, much work remains to understand the bat colony. Among the questions Dr. Thong plans to address in the near future are where the wrinkle-lipped bats spend the rest of their year, as well as where and how they forage locally.

“It’s a very big question, where they go when they’re not at Tan Lap,” Dr. Thong says. “Or even where they go every night. We see that they fly very high up after they emerge, and they seem to go very far away. We just don’t know where they go.”

Dr. Jon Flanders, BCI’s endangered species intervention program director, said the work could not have been accomplished without Dr. Thong’s close collaboration with local partners, and it serves as a model for other conservation projects in Vietnam and Southeast Asia.

“Without his input in Vietnam, there wouldn’t be as much research, and without the research, there wouldn’t be the conservation,” Dr. Flanders says. “The work he’s done in Vietnam has been exceptional, and it’s critical for bat research and conservation across the whole country.”

Dr. Thong and BCI also helped facilitate the renewal of a 10-year protection and management agreement between the landowner and local governmental agencies, Dr. Flanders added.
By and large, the people of Tan Lap have also adopted a new attitude toward “their” bats.

“At the beginning, people didn’t understand the importance of bat conservation,” Dr. Flanders says. “But now they understand that to conserve a bat cave is not only important for the bats’ survival, but their own local identity. They’re very proud of their cave. It’s the only one in Vietnam with millions of bats in it, and they’re the ones taking care of it.”

[Sidebar]

Critical Need: Cave Conservation

Broadly distributed throughout all the countries of Southeast Asia, Tadarida plicata is listed as “Least Concern” on the IUCN Red List.

However, with its habit of forming extremely large colonies—hundreds of thousands to millions of individuals per roost—in relatively few caves, even moderate impacts on cave roost sites stand to levy an outsized toll on this bat species. Yet throughout T. plicata’s range, caves are under threat from mining, development, tourism, and general human disturbance.

Dr. Vu Dinh Thong’s work at the cave at Tan Lap in Vietnam not only helps protect a vital link in the local and regional ecosystem chain—the bats themselves—but also provides a model for how to protect more critical cave habitats across Southeast Asia and the world.

Establishing a Bat Guard 

BCI’s emergency conservation grant enabled bat researcher Dr. Vu Dinh Thong to do more than just conduct scientific surveys at Tan Lap Cave. It also helped him establish a network of local conservationists to amplify his own work.

Through formal and informal meetings and workshops in schools and community centers, and at gatherings of local clubs and societies, Dr. Thong recruited students, teachers, residents, and local authorities. With their help, Dr. Thong was able to relay interesting and important information obtained through field surveys about the colony of wrinkle-lipped free-tailed bats (Tadarida plicata) and five other species of bats living in the local cave.

Armed with “bat swag” that included T-shirts, mugs, calendars, posters, and CDs with informational video clips on the bats and their benefits, Dr. Thong and his conservation network fanned out across the community to raise awareness of, and urge immediate and long-term protection for, the largest bat colony in all of Vietnam.

Hungry for (Plant)hoppers

The smallest species in its genus, the velvety dark-brown wrinkle-lipped bat (Tadarida plicata) only weighs around half an ounce—but collectively, colonies of these bats pack a powerful punch.

In one study of this bat species’ diet, researchers found T. plicata consumed at least nine insect orders, including leafhoppers, beetles, moths, dragonflies, and grasshoppers. White-backed planthopper (Sogatella furcifera) is a particular favorite and—as a major pest and disease vector of rice in Asian countries—the more of them that bats gobble, the better.

Bat-provided pest control becomes even more important in light of findings that show planthoppers’ resistance to common pesticides has grown since the 1980s. Despite being increasingly unaffected by organophosphates, pyrethorids, pymetrozin, and neonicotinoids, planthoppers stand no chance against the appetites of a hungry bat swarm: The diet study found nearly 30% of insect remains in T. plicata droppings comprised of white-backed planthoppers.

 

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