The Atlas Obscura Podcast · Monday, August 31, 2026
Ryan Huling, author of "The Hidden Nation of Animals," described how up to 10 million Mexican free-tailed bats converge in Bracken Cave near San Antonio, Texas, forming the largest congregation of non-human mammals on Earth. This massive aggregation occurs annually as the bats migrate from Mexico for the spring and summer months.
“For at least 8,500 years, or possibly as many as 10,000 years, the bat community inside of Bracken Cave, which is again, just on the suburbs of San Antonio, so surrounded by human infrastructure, swells exponentially every spring as up to 10 million freetailed bats fly 700 miles north from various smaller roosts in and around Central Mexico.”
“And after mother bats give birth to their pups, the population doubles again to nearly 20 million, which is the largest congregation of non-human mammals on earth.”
“Mexican freetailed bats spend their winter months in the caves of Mexico to beat the Texas frost.”