Hot on the Trail of Brazil’s Bat Caves

For years, Barros has studied hot caves, rare systems occupied by enormous colonies of bats from the Mormoopidae family. The bats congregate by the tens or even hundreds of thousands in specifically shaped cave environments where they can generate enough body heat to keep their pups—which are born without fur—warm. Their guano contributes to the process as well, fermenting and generating additional heat.

“They are creating the environment that they need to survive and thrive in,” Barros says. The result is a unique ecosystem that supports not only the bats themselves, but a broader community of cave-dwelling wildlife.

Brazil is home to more than 30,000 registered caves, but until recently, fewer than 20 were known to qualify as hot caves. Through BCI’s Brazil Program and its partnership with the National Center for Cave Research and Conservation (CECAV), Barros and her colleagues are working to assess caves across the country, identify vulnerable bat populations, and prioritize conservation efforts.

So far, the team has surveyed more than 100 caves in 13 Brazilian states. In the process, they have confirmed six previously unknown hot caves: one in the Amazon, two in the Caatinga, and three in the Cerrado, the first hot caves ever documented in that biome. The discoveries also represent the first confirmed hot caves for the states of Amapá, Alagoas, Bahia, Goiás, Tocantins, and Mato Grosso.

The researchers aren’t just looking for the caves; they’re also counting bat populations. To determine colony sizes, they film bats emerging from the caves and analyze the footage with specialized software that counts bats exiting and entering, producing an estimate of the total population. One newly documented cave in Amapá hosts more than 162,000 bats, while another in Tocantins supports nearly 158,000.

Hot caves are important because they can serve as maternity roosts for bat species in the Mormoopidae and Natalidae families, which include furless pups. “For the puppies to survive, they need to maintain the temperature,” Barros says. But these sites face growing threats that put the bat populations at risk, such as deforestation and poorly targeted vampire bat control programs.

The biggest threat, however, is habitat degradation and destruction from nearby mining. While caves with Endangered species are fully protected by federal law, hot caves can be destroyed if companies compensate. This means they would need to protect two caves for the one destroyed, which should be equivalent in characteristics to the one being destroyed. However, this is generally not possible.

“These caves are crucial,” she says. “Not only for these bats, and the other cave-dwelling species, but also for people, too.”