Largest bat colony (current)

Today, the largest colony of bats known is thought to be the colony of Brazilian free-tailed bats (Tadarida brasiliensis) at Bracken Cave, near San Antonio in Texas, USA. Flocks of bats can be tracked on weather radar as they exit the cave. Some estimate that at least 15 million bats aggregate at Bracken cave in summer, although accurate counts of such large numbers of bats at twilight are challenging, and recent estimates using thermal imaging and weather radar surveillance suggest that numbers may be as much as an order of magnitude lower.