Local residents report that shortly after the removal of the railroad tracks in 1942, bats moved into the tunnel. In July and August there are over three million Mexican Free-tailed bats (Tadarida brasiliensis) and 1,000-3,000 Cave Myotis (Myotis velifer) in Old Tunnel. The Mexican Free-tailed bat is a medium-sized bat, weighing about 12-15 grams (12 paperclips). They are named for the tail that hangs free from the uropatagium (skin between hind legs and tail). The title "Mexican" is added to their name because they migrate to Mexico in the winter months. Old Tunnel bats usually leave the tunnel in late October, and fly to Mexico. During this migration, they can fly at altitudes of 10,000 feet and speeds of 60 mph.

A Year in the Life of The Old Tunnel Bats: While in Mexico, these bats mate during February and March when the females are most fertile. Bats returning to Texas in late March or early April include pregnant females who give birth to one single pup (baby bat) during June. The pups are not born in the tunnel, but in other nearby caves or under bridges where the temperature and humidity levels are more stable. The tunnel is only 920 feet long and is open at both ends, and therefore, the temperature and humidity very greatly. The Old Tunnel is considered a pseudo-maternal colony because there are both pregnant and lactating females in the tunnel, but there are no pups. Pups usually fly within four to six weeks after birth and are considered juveniles when they travel to the tunnel with their mothers. Bat populations in the Old Tunnel increase substantially when the females return from maternity colonies along with the juveniles in late July and early August. Joining the Old Tunnel population in September and October, are bat migrating south from further north in the United States. This process of "staging" occurs when bats group together before flying to Mexico for the winter.
Bats swarming from the tunnel entrance at the Old Tunnel WMA.

What Happens When the Sun Goes Down: On summer nights, the Old Tunnel bats usually emerge within an hour before or after sunset. Most bats exit through the south end of the tunnel, spiraling in a counter-clockwise direction in order to gain altitude over nearby trees (click here to view video images of bat emergences). Red-tailed hawks are sometimes seen feeding on the bats as they emerge, however these and other predators do not impact the bat population. The large serpentine column travels southeast towards the Guadalupe River. Bats also exit from the north end of the tunnel, and fly either north towards the Pedernales River, or south over the Old Tunnels' observation deck. After getting water from local water supplies, the colony disperses to feed in smaller groups. Eighty percent of the Free-tail's diet includes agricultural pests such as the cutworm, cornborer and webworm moths. Each can eat its weight in insects nightly, and the whole colony may devour over 25 tons of moths per night. The bats return to the tunnel between midnight and daybreak, having traveled an average 25 to 30 miles to forage.
Good Ole' Bat Guano

Huge deposits of droppings in the roosts of Mexican Free-tails have earned them the common name, "Guano bat". Bat guano (droppings) from insectivorous bats was an important source of fertilizer, and is still sold as an expensive, organic fertilizer. Before the oil boom, guano was Texas' number one mineral export. Many have tried to harvest guano from Old Tunnel. However, natural springs within the tunnel made the operation too difficult. Many Free-tailed colonies consist of at least one-million bats, and the resulting concentration of ammonia is extremely high. In fact, many people can identify these bats by the distinctive odor.
Hiking is an enjoyable activity that is available in many of the Wildlife Management Areas of Texas. Since potable water is not available on many of the Wildlife Management Areas, it is a good idea to bring plenty of drinking water.
Old Tunnel Nature Trail

Old Tunnel Nature Trail

The Old Tunnel WMA nature trail is less than one half mile in length, and is open to the public 365 days a year from sunrise to sunset. During the months that the bats are in residence at Old Tunnel, the trail will be closed each evening. Monday through Wednesday evenings the trail and lower viewing area are not open to the public. On Thursday through Sunday evenings, the trail will only be open to those visitors who pay admission to view the bats at the lower viewing area. The trail is primitive and can be steep. No drinking water, food, or man-made shelter is available on the trail. No water fountains or other water is available on site, and carrying drinking water is recommended. Trail guides are available for the public at the iron ranger located at the lower viewing area. Numbered markers designate stops along the trail, and corresponding information regarding each stop is explained within the guide.

Although entrance into the tunnel is prohibited, visitors are encouraged to enjoy the view of the tunnel from the trail. Throughout the day, from April to October, bats can be seen flying within the tunnel. In order to minimize disturbance to the bat colony and for the safety of our visitors, all guests must stay on the designated trail. Under no conditions are visitors allowed to approach the tunnel.

Guided nature walks are also offered at Old Tunnel WMA. The walks are usually informal and cover a variety of topics, such as bird watching, plant identification, and astronomy.

Special Group Tours are conducted at the lower viewing area Monday through Wednesday evenings, May through October, for organized groups of up to 70 people. Reservations are required. Passports or permits, including the Texas State Parks Pass, are not accepted. Special Group Tour fees are as follows: Youth Groups: $40.00; Non-Youth Groups: $75.00. To schedule a Special Group Tour, please call (830) 990-2659.

Dates Open: Open year-round from sunrise to sunset for general use.
Bat viewing nightly May-October. The trail to the lower viewing area is closed each evening. Monday through Wednesday evenings the trail and lower viewing area are not open to the public. On Thursday through Sunday evenings, the trail will only be open to those visitors who pay admission to view the bats at the lower viewing area. For the most up-to-date emergence information, call the toll-free information line at 1-866-978-2287.

Rules:

* No overnight camping allowed
* No pets are allowed
* No public consumption or display of alcohol
* No smoking is allowed at the upper and lower viewing areas
* No firearms or hunting allowed
* No fires of any type are allowed
* Bicycles, motorized vehicles, or horses are not permitted
* Removal of plants, rocks, animals, or cultural items strictly prohibited
* Please stay on designated trails; entering the tunnel is strictly prohibited
* Handicapped access is available when TPWD staff or volunteers are present or upon special request
* For the protection of the bats and for your own safety, please do not handle or otherwise disturb bats