From May to October, Old Tunnel Wildlife Management Area is home to about 3 million Mexican free-tailed bats and 3,000 Cave myotis bats. Each night during this time, the bats spiral upward once or twice outside the tunnel entrance before streaming out to feed on insects. Aerial predators such as Red-tailed Hawks and terrestrial predators such as raccoons sometimes feed on fallen bats as they emerge. Texas Parks and Wildlife Department acquired the property in 1991 to protect and preserve the bat colony, because increased disturbance from growing numbers of visitors might cause the bats to abandon the roost. Biologists have also learned much from research performed at Old Tunnel. Even when the bats are not present, visitors can use the historic railbed trail to see the tunnel that changed history in the Hill Country.