I drove to Sarapiquí, a little-known region in Costa Rica, during a brief respite of dry weather between Hurricanes Eta and Iota in search of a miniature tropical bat. Here, conservation efforts big and small are fighting to preserve a lowland tropical rainforest with astonishing biodiversity, including one of the smallest and most adorable mammals: Ectophylla alba, also known as the Honduran white bat or Caribbean tent-making bat.
It was impossible not to coo
I'd been warned that these bats aren't always easy to find. They live in selected lowland rainforest habitats from Honduras to eastern Panama. In Costa Rica, I tried my luck at Tirimbina Rainforest Center, a 345-hectare private reserve. At first glance, the neighbourhood seemed an unlikely locale for a rainforest. Pineapple plantations dominated on all sides and spiky green shrubs stretched to the horizon. But tucked away behind an unassuming green gate was an ecological oasis that protects nearly 4,000 species of plants and animals.
My guide, Emmanuel Rojas Valerio, led me across a 270m chain-linked suspension bridge over the roaring Sarapiquí River. In the middle of the river was the small island of "La Isla", once a biologist's heaven for studying the bats due to its abundance of heliconia plants. The tent-making bats chew a perforated ridge into heliconia leaves, similar in shape to banana leaves, to form tents where they roost during the day. The plants are easily shaken, which is one of the reasons they make suitable homes. The leaves become alarm bells as soon as predators, such as snakes, owls and opossums, touch them, giving the bats a chance to escape.
In 2015, severe flooding wiped out La Isla. Though, by the look of it now, I wouldn't have known. Enormous cecropia and balsa trees had already grown taller than the bridge, and dense vegetation obscured the island floor. The tiny bats, however, haven't yet returned. Scientists speculate that the understory is too crowded with new growth, making it hard for them to easily leave their tents.
But we were lucky that day. Inside the reserve, just a few hundred meters after the bridge, Rojas Valerio pointed out fraying empty tents along our trail, then led me into marshy woods with mud up to our ankles. In the middle was a neatly folded leaf with a brown ridge on top. Underneath, the bats looked like a handful of fuzzy green seeds, a surprisingly effective form of camouflage. When Rojas Valerio turned on his torch, they transformed into white cotton balls with yellow-orange noses and ears. A shiver ran through the upside-down colony of five females, one male and a baby. One opened its eyes and stared at us, dewy black slits embedded in snowy fur.
It was impossible not to coo. One of the smallest fruit-eating bats in the world, the tent-making bat has an average wingspan of just 10cm and weighs roughly 6g – about a teaspoon-and-a-half of sugar. According to Bernal Rodriguez, bat biologist and professor at the University of Costa Rica, these diminutive creatures are the only known mammals with an accumulation of carotenoid pigment, the chemical that accounts for the bright yellow of their ears and nose. The carotenoid comes from peels of the bats' food: cranberry-like figs from a particular tree, Ficus columbrinae, that grow near rivers. Recent studies by Rodriguez and his team suggest that the colouring is a trait of sexual selection. Males that are larger and well fed have brighter colours, a feature that attracts females.
Rojas Valerio explained that the colony we found will leave their roost at sundown to travel nearly a kilometre to the riverbank for figs, and only figs. "They don't always come back to the same tent," he said. "They make many houses where they can stop along the way. But always in heliconia leaves."
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Specialists, not generalists
It's this specialisation that makes the tent-making bat, now classified as a near threatened species, vulnerable. "[The bats] have to live near the ficus, which means that their habitat is very specific," said Rodriguez, who has been studying the species for decades. "That's why you see the bat in one place and then walk just a few kilometres and cannot see any."
If eating only one type of food and living in only one type of home weren't specialised enough, tent-making bats also prefer specific moments in a forest's life cycle. They need enough sunlight to reach the forest floor to camouflage in their heliconia tents and stay warm, and also enough canopy cover to protect them from rain and wind. As a forest matures and the canopy becomes denser, conditions become less hospitable.
Forest regeneration, the process by which old growth dies and makes room for new growth, is essential to protecting this species. The largest reserve in Sarapiquí, La Selva, used to have many colonies of tent-making bats, but their numbers reduced as canopy cover increased. Years from now, that may change as older trees fall, again creating favourable conditions for the bats. La Selva, one of the oldest research stations in the country, maintains an important biological corridor with Braulio Carrillo National Park, a large swath of virgin forest. A pioneer in the private conservation movement, La Selva has inspired dozens of smaller reserves, such as Tirimbina, that work together to safeguard forest cover.
"In general, it's better to have a big patch of forest than disconnected patches. You're able to sustain more species populations and have less of a border effect," said Amanda Vicente Santos, a researcher at Emory University in Atlanta, Georgia and former student of Rodriguez. Vicente Santos examines the immunology of bats to better understand human impact on tropical ecosystems. Often, it's at the borders between habitats where species trade diseases or show distress that is predictive of broader consequences.
While tent-making bats do well close to rivers where food is abundant, Vicente Santos makes clear that they need a "constant natural succession of plants without humans". Forests like Tirimbina and La Selva, where regeneration is constant, are critical to maintaining their numbers.
Education as conservation
Bats have long been maligned as bloodthirsty symbols of horror, and the link between the coronavirus pandemic and bats hasn't helped. With numerous bat-focused tours across the country and host to more that 100 species, Costa Rica has become a myth-busting leader. Annabelle Nuñez Porras who cares for orphaned baby bats at the Bat Jungle, a conservation organisation in Monteverde, Costa Rica, says that the stereotypes are completely at odds with bats' true nature. "Bats are not fighters," Nuñez Porras said. "They generally share space and food and live in harmony [with each other].” Tent-making bats, described as "cute" even in scientific journals like the Journal of Mammalogy, are particularly useful in combating misconceptions and inspiring conservation.
The stereotypes are completely at odds with bats' true nature
Tirimbina's approach emphasises local engagement. "We want people who live around here to connect to nature," said Mariela Garcia Sánchez, a biologist and Tirimbina's education director. For more than 20 years, the reserve has been leading free environmental education classes for nearby public schools. Until the pandemic hit, roughly 1,500 children participated annually in these programmes. "In their preschool books, these kids see lions, giraffes and elephants," said Garcia Sánchez, who leads the classes. "But where are the ectophylla and tolomucos [tayras – weasel-like mammals], the animals in their community? Without education, there is no conservation."
In Sarapiquí, where many people rely on plantation work for income, building awareness around conservation has taken time. Rojas Valerio, born and raised not far from Tirimbina, says he was interested in wildlife as a child, but for years the only work he could find was in pineapple plantations and selling tropical birds. At one point, he owned 50 birds, most of them ones he caught himself.
In 2004, Rojas Valerio joined Tirimbina by happenstance for a two-week construction job. He soon began helping visiting biologists and learning to identify different species. But his employment had one contingency. "I had to free the birds I was keeping," he said.
Not long after, Rojas Valerio started working with Rodriguez as a field assistant, a job that became the education he'd never had. He's since contributed to scientific papers on bats and birds, produced his own research questions and attended ecology conferences across Latin America. "I never expected to be part of the scientific learning, to be producing knowledge," he said.
Conservation and education efforts have a direct impact in the community where he lives. Caging and selling birds and killing bats used to be common practices. "Now many of the kids we educated years ago are parents who value and connect to nature," said Rojas Valerio. "They come to the reserve and ask to see the little white bats."
Where to see the bats
Travellers can support bat conservation and learn more about bats through reserves and conservation groups throughout Costa Rica.
Tirimbina Rainforest Center offers educational day and night tours. When available, visitors can observe evening mist netting investigations where bat specialists carefully capture and release bats as part of a 10-year data collection effort to track bat populations in the reserve. The experience includes information on myths and ecological benefits of bats. The reserve also has accommodations and an onsite restaurant.
The Bat Jungle in Monteverde, a mountainous cloud forest region on Costa Rica’s Pacific side, offers 45-minute guided tours of its bat enclosure. Though tent-making bats are not native to the area and so aren’t part of the exhibit, visitors can see eight different species of fruit and nectar-eating bats. Most are long-term residents that were found either orphaned or injured and could not return to the wild. Visitors can observe bat behaviour up close and hear echolocation, the soundwaves bats use to locate objects, in real time through ultrasonic microphones.
While not specific to bats, La Selva Research Station offers guided day and night tours through its 61km of trails. In addition to tent-making bats, La Selva has logged more than 60 other bat species in the reserve. Accommodations and an onsite restaurant are also available.
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