In the smallest of Texas state parks, in a historic railroad tunnel of only 920 feet, three million bats compactly roost during warm summer days to emerge in the evening to the delight of bat viewers.

Millions of bats stream from Old Tunnel. Photo courtesy of Texas Parks and Wildlife Department.
Bat flight at Old Tunnel is impressive. Photograph by Nyta Brown. Courtesy of Texas Parks and Wildlife Department.

From 1917  to 1942, railroad travelers on the San Antonio, Fredericksburg, and Northern Railway glided through an impressive dark tunnel. When the rail line closed permanently, scores of migratory bats glided in.

Today Old Tunnel is the summer roost for an estimated three million Mexican free-tailed bats (Tadarida brasiliensis) and 1,000 to 3,000 cave myotis (Myotis velifer). Bats emerge nightly, weather permitting, between May and October. However, the size of the colony varies through the season. Peak numbers of bats are generally seen from mid-August into the first weeks of September.

Old Tunnel is considered a pseudo-maternity roost. Because the tunnel is open at both ends and temperatures are unstable, bat pups are not born in the tunnel but in nearby caves or bridges. Pregnant bats roost in Old Tunnel until they are ready to give birth. Lactating bat moms return to Old Tunnel with their bat pups.


  • Tickets are required for everyone, including children, in the state park after 5 PM.
  • Nearby Fredericksburg, where Old Tunnel is located, is becoming increasingly popular for its agritourism. Travelers to the area often visit wineries, peach tree groves, herb farms, and lavender fields before bat viewing in the evening.  
  • Also, check out other Texas bat-viewing sites. Of note, Texas is home to 32 of 47 bat species found in the United States.