Old Tunnel State Park

Park Alert... 

Nature

Old Tunnel is home to up to 3 million Mexican free-tailed bats (Tadarida brasilienses mexicana) and 3,000 cave myotis bats (Myotis velifer) from May through October.

Bat flying with outstretched wings
Bruce D. Taubert/Minden Pictures /Bat Conservation International

During these months, millions of Mexican free-tailed bats spend their days in the tunnel and their nights on the wing. The tunnel provides them a secure roosting place and protection from predators while they rest.

This is a pseudo-maternal colony. In the spring, female Mexican free-tailed bats migrate to Old Tunnel, but they leave to have their babies elsewhere. Male bats then move in.

In August, the females return with their babies and the population of the tunnel balloons to about three million bats.

The evening bat flight is at its most astounding then. Millions of bats spiral out of the tunnel each evening, gaining speed and altitude before spreading out to hunt insects overnight.

Bats leave for warmer climates when the weather cools down. The tunnel is mostly empty until spring when the cycle begins again.