At dusk each summer, the skies over Bracken Cave fill with bats, pouring from the entrance of the ancient sinkhole.
An estimated twenty million tiny flying mammals take up residence in this cave between March and October, making it not only the largest such colony of bats, but perhaps the largest concentration of mammals anywhere in the world. The little bats fly about 1,000 miles from Mexico to their summer home, where they give birth to the next generation.
The Mexican free tailed bat is one of the most abundant mammals in North America, and is the state bat of Texas, which has colonies in several locations, most famously living under the Congress Street Bridge in Austin. While holding quite a standing in the Lone Star State, Central America and Mexico are also places the bats are known to reside.
But the bats may be in trouble: The organization Bat Conservation International, who owns the property on which the cave sits, has issued statements warning that the bat colony may be under threat from a proposed large development project on adjacent property.
To protect the bats, access to the cave and surrounding property is strictly controlled by Bat Conservation International, who make it open to the public for viewing on select summer nights only.