Devil’s Sinkhole – Bat-Watching
Every summer evening, millions of bats emerge from Devil’s Sinkhole near Rocksprings, Texas. Guided tours of the phenomenon being at the Rocksprings visitor center.
Bats have likely called the Sinkhole home for centuries but first attracted significant attention in the 1970s. In 1985, the Texas Parks and Wildlife Department acquired the site, a cactus-studded limestone ridge overlooking miles of open country, and in 2002, the Devil’s Sinkhole Society began offering tours. Texas’ third-largest cave, the 360-foot deep Sinkhole formed several thousand years ago when porous limestone collapsed after underground water receded. Its shelter and rough stone provide an ideal roost for the free-tailed bats (Tadarida brasiliensis Mexicana), with as many as 200 adults or 500 pups per square foot.
Bats Important Part of Natural Environment, Control Insects
These hummingbird-sized mammals spend the night foraging as far as 75 miles away, eating up to their weight in insects each night. Nursing mothers consume more, and the colony collectively consumes some 20 tons of bugs each night, a weight equivalent to ten full-grown elephants. “Imagine if they didn’t do that,” says Devil’s Sinkhole Society volunteer guide and Rocksprings resident Ben Banahan. “Farmers and residents would really notice.”
Acrobatic flight and average speeds of 25 miles per hour allow the free-tailed bats to catch insects on the wing, aided by powerful echolocation. Emitting high-frequency chirps, they measure the echoes to identify beetles, moths, and other prey. Because these bats sound with an open mouth, they have often photographed that way, which makes them appear fierce although they are quite harmless. These bats reside in Mexico during the winter, then follow spring temperatures–and insects–here, generally remaining through October. When the bats depart, thousands of swallows move in.
A sturdy viewing platform affords a heart-thumping peek into those first 150 vertical feet, but only the bats and a few hardy cavers had seen the rest of the Sinkhole.
“It’s been one of our weak points, that we don’t actually take you into the cave,” says Banahan. Of course, seeing the bats makes up for that.” Soon the Rocksprings visitors center will offer a virtual journey into the cave, courtesy of 3D glasses and two state-of-the-art technologies, LiDAR, or Light Detection and Ranging, and 3D Photo Real Modeling. A collaborative effort of Dallas-based Real Earth Models, the Texas Cave Management Association, Kevin McGowan Photography, Texas Parks and Wildlife Department, and the Texas Bureau of Economic Geology, the virtual tour is accurate to within half an inch. It will show a realistic portrayal of the cave complete with colors, cracks, stains, and shadows.
In addition to controlling agricultural pests, bats are also crucial to pollination and seed dispersal in many ecosystems, including deserts of the southwestern United States and the Amazon rainforest. The flying mammals have been around for 50 million years and live on every continent except Antarctica.
Devil’s Sinkhole State Natural Area Hiking, Nature Tours
Tours of the bat emergence are held Wednesday through Sunday evenings mid-April through October. Reservations can be made by phone, 830-683-BATS (2287). Spanish-speaking guides are available. The Society also offers guided day tours and nature hikes (bats will not be seen on these). The Rocksprings Hotel, a block from the visitor center, offers overnight accommodations, as do a number of hotels and bed and breakfasts in Junction, a 45-minute drive from Rocksprings.
Devil’s Sinkhole is only one of a half-dozen bat viewing sites in Central Texas. Find others through Austin-based Bat Conservation International.