mell announces the bats before sight. The sharp aroma of 15 million bats carried on a cool evening after the rains. Recent storms had grounded the colony the night before, so tonight they were hungry. Scout bats tested the air first, darting in tight loops. Then the waves of bats came in quick succession, creating a spiraling mass at the cave mouth before the column bent southeast toward the agricultural fields, the stream of bats swaying left and right like one breathing organism. When the wave swayed directly overhead, the wing beats stirred a breeze against my skin and filled the air with a low, steady drumming. It looked like a waterfall running upwards, with no visible end.

Despite being born and raised in Texas, this was my first Bracken experience, in the days before I officially stepped into this role. What stayed with me wasn’t just the scale, though I’m still not sure how to process 20 million of anything. It was the thought that this same thing was happening in roosts and caves around the world that night, and that Bat Conservation International’s work is what stands behind protecting them.

an a bat be both abundant and Threatened at the same time? In the case of the Harrison’s large-eared giant mastiff bat (Otomops harrisoni), the answer might be yes. Known from only two cave roosting sites located about 500 miles apart in Kenya, this bat was only recognized as a distinct species a decade or so ago, based on genetic evidence distinguishing it from its sister species, the large-eared free-tailed bat (Otomops martiensseni).

The Kenyan caves where the species roosts range from large basalt tubes to vast, high-ceiled cave chambers. One roosting site, Chyulu Hills, is a national park, while the other, Mount Suswa, is a community conservancy managed by local community representatives.

ost people come to Bracken Cave Preserve for the bats, since it’s home to the largest known bat colony in the world. On summer evenings north of San Antonio, visitors gather in the viewing area, waiting for the first movement at the cave mouth. Then the spiral begins: more than 15 million Mexican free-tailed bats (Tadarida brasiliensis) pour into the sky in an inky black ribbon that twists upward before spreading across the Hill Country.

What most visitors don’t see, or even think about, is what happens before and after the bat flights.

Earlier that same day, volunteers may have been clearing trails in the Texas heat, leading a butterfly survey, searching for hard-to-find Endangered plants, or teaching children why bats matter to Texas ecosystems.

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.

he wide beam of my spotlight illuminates a small, furry creature suspended in mid-air. The bat is caught in a fine net stretched over Gallinas Creek in the Sangre de Cristo mountains in northern New Mexico. As one of BCI’s biologists and trainers on the project, I guide a fellow scientist through the process of untangling the bat. First, we identify which side of the net it entered from. Then, we slowly work the fine strands off the bat’s back and over its elbows, wrists, and head.

It’s 8 p.m., and our work is just beginning. We are surrounded by the soothing sounds of the creek, the brilliance of the night sky, and great bat habitat. Looming in the distance is the bare-rock face of Hermit’s Peak, and a ponderosa pine forest surrounds us. Some trees are green while others are charred. This canyon was caught in the confluence of the Hermit’s Peak and Calf Canyon fires, which together in the spring of 2022 burned 340,000 acres, making it the largest recorded wildfire in New Mexico’s history.

The cave branches through hundreds of feet of subterranean habitat, with multiple openings above ground. BCI’s Senior Habitat Restoration Specialist Dan Taylor says protecting such a cave is important for bats.

“The more complex a cave, the better, because these caves have habitats with different microclimates that bats can take advantage of,” Taylor says. “Some parts of a cave may be cooler, therefore better for hibernation. Others are much warmer and better for birthing and raising pups. This cave, with its complex structure and multiple openings, is such a cave.”

The cave served as nature’s perfect museum, with the dry, stable environment preserving the animals after they died of natural causes. Since the discovery, researchers evaluated some specimens’ ages through radiocarbon dating and found the bats are thousands of years old. Some specimens even exceeded the upper limit of radiocarbon dating, meaning they are more than 50,000 years old.

These initial results demonstrate that bats have continuously occupied the cave system for millennia, illustrating the importance of caves, which serve as habitat anchors through changing climate eras.

ina Cheng, Ph.D., BCI’s Director of White-Nose Syndrome (WNS) Research, collaborates with scientists, wildlife managers, and policy makers across North America to better understand WNS and develop tools to combat it. Among the most promising tools is a groundbreaking fungal vaccine developed by researchers at the U.S. Geological Survey (USGS) that has been shown to reduce disease severity and increase survival in vaccinated bats.

WNS is a disease caused by an invasive fungal pathogen, Pseudogymnoascus destructans (Pd). Pd is believed to have been introduced to North America in the mid-2000s, likely from Eurasia, where it is endemic. There are a dozen bat species that have contracted WNS in North America, but three species have been particularly hard hit: the little brown bat (Myotis lucifugus), tricolored bat (Perimyotis subflavus), and northern long-eared bat (Myotis septentrionalis).