Protecting bat cave will benefit region

North of San Antonio, the world's largest bat colony is growing bigger. Mexican free-tailed bats, Tadarida brasiliensis, are arriving at Bracken Cave from across the country, stopping there to fatten up on insects before their annual long flight to Mexico.

Bracken's 15 million bats consume more than 100 tons of insects each night from March through mid-November. Bats save central Texas cotton farmers about $75 per acre in pest control, and a 2011 article in Science estimated the total value of bats to U.S. agriculture at roughly $23 billion a year.

But bats are declining. A fungus from Europe has killed more than 7 million bats of other species in the Midwest and Northeast United States. Wind energy turbines are now believed to kill 200,000 U.S. bats annually; that figure will continue to rise as more wind farms are built.

Habitat loss, though, is the biggest problem for bats. Increasing development of the Hill Country will push bats and people together, with serious consequences for both.

Along rapidly developing Interstate 35, developer Brad Galo is proposing to build 3,500 houses on 1,500 acres adjacent to Bracken Cave. Free-tails are attracted to buildings, and the 3,500 houses proposed for the Crescent Hills subdivision lie under the nightly three- to four-hour flight path of Bracken's bats.

This will put Crescent Hills' 10,000 future residents into regular contact with Bracken's 15 million bats. Although the incidence of rabies in bats is quite low, it's endemic and fatal to Texas wildlife, and 16 percent of dead bats tested in 2012 by the Texas Department of State Health Services were positive for rabies. Building Crescent Hills will create a potentially serious public health problem when bats show up under eaves, on porches and around backyard swimming pools, looking for roosts or following insects drawn to lights and water.

Our organization hopes to protect the Crescent Hills tract, but we need help from the city and other public agencies. There is good reason for all to participate. Federally endangered golden-cheeked warblers abound. The proposed Crescent Hills subdivision lies over an aquifer recharge zone important to maintaining groundwater reserves immediately north of the city and to preserving the San Marcos and Comal springs, which San Antonio has pledged to protect under the Edwards Aquifer Recovery Implementation Plan.

If Crescent Hills is approved by San Antonio, however, the city will have to pay to help put it there. The San Antonio Water System, SAWS, will spend up to $4 million to provide water and sewer service to the development, even though it lies beyond the city limits. In other words, the city will spend millions of dollars to send San Antonio's drinking water beyond the city limits to communities in Comal County that don't pay city taxes, creating a public health problem in the process.

Protecting Crescent Hills, conversely, would consolidate conservation lands in the vicinity, providing more than 4,000 acres of contiguous open space and aquifer recharge, extending into Bexar County along Cibolo Creek. This would create a major new park and preserve — not unlike the Government Canyon State Natural Area.

Public opinion will turn against Bracken's bats if a steady stream of Crescent Hills children and adults is required to receive expensive, preventive rabies shots from chance encounters with bats — as occurred in three San Antonio schools earlier this year — or, in the worst case, an unvaccinated pet or person contracts rabies from a resting, sick or dead bat found in a yard or carried into a house by a child or family dog or cat.

San Antonio rightly spends most of its aquifer protection funds on lands west of the city, from which most of our groundwater flows. But in the future, all groundwater basins surrounding the city will be vital to its well-being. The Crescent Hills tract is a worthy addition to the city's groundwater protection portfolio.

The mayor, City Council and officials in Bexar County and the Legislature are taking this issue seriously. Councilman Ron Nirenberg, state Rep. Lyle Larson and Bexar County Commissioner Kevin Wolff have been particularly effective at bringing all parties to the table, and Galo has shown a willingness to find a solution. Comal County leaders have yet to weigh in. It will take considerable private philanthropy and political will to ensure this area remains forever wild and the world's largest bat colony has a future. It will be a poorer and buggier world if San Antonio's bats are only the paper and plastic kind.

Andrew Walker is executive director of Bat Conservation International.