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Bracken cave: Scientists monitoring deadly bat-cave fungus

Bracken Cave shows no signs of white-nose syndrome — for now

Fungus generic picture

Bat Conservation International scientists are working to slow the spread of a potentially deadly fungus discovered in Bracken Cave, regarded as the summer home of the world’s largest bat colony.

Pseudogymnoascus destructans, or Pd, is an invasive glop. It generates the white-nose syndrome disease, a killer of hibernating bats.

BCI announced in May the detection of Pd at the preserve north of Garden Ridge.

“The bats starve to death,” said Fran Hutchins, BCI’s director of Bracken Cave.

Despite ever-increasing Pd, researchers are confident there’s no local trace of WNS and it may take years for the disease to manifest.

Skin swabs to test for the fungus’ presence were performed on the mammals between December 2018 and April 2019.

BCI, along with The Nature Conservancy, took over the cave in 2014 after San Antonio politicos approved partnerships with those groups and other entities to safeguard it from development.

Located near FM 3009, Bracken Cave houses more than 15 million Mexican free-tailed bats.

The underground chambers also serve as a maternity site for pregnant bats, causing the cave’s population to nearly double.

WNS occurs when the fungus proliferates in the creatures’ nose, mouth and wings, rapidly waking them up from dormancy during winter and exhausting energy reserves before spring.

Since emerging in 2007, the scourge has killed millions of hibernating bats in the eastern United States.

Pd has been a menace across the state since 2017, and has spread through 22 sites in 16 counties, 11 of which were exposed to the fungus just this year, according to the Texas Parks & Wildlife Department.

Statewide, the fungus was found on 13 Mexican free-tailed bats, four tricolored ones and 43 cave myotis.

There’s no known cure for the plague, Hutchins said; the next step is developing ways to aid in the bats’ survivability.

The flying mammals’ rapacious consumption of insects is vital to the ecosystem; recent studies indicate the value of bats to Texas farmers is estimated at $6.4 million per annual cotton harvest.

By limiting the insect population, the bats account for a reduction of crop loss, help prevent the spread of crop disease, and lessen the need for pesticide application.

Hutchins said humans aren’t in jeopardy of contracting the virus.

Access to Bracken Cave is limited to “small, reserved groups,” according to the cavern’s website, plus individuals must be BCI members to participate in the bat-flight exhibits, held May through September.

The Bracken Cave Preserve has sheltered bats for 10,000 years, said biologists.

In addition to being home to millions of bats each year, the cave in southwest Comal County harbors some federally protected endangered species, and it sits atop the Edwards Aquifer Recharge Zone.

On Oct. 16, 2014, the San Antonio City Council approved a $20.5 million deal – led by then-District 8 Councilman Ron Nirenberg, now the mayor – to purchase 1,521 acres surrounding the bat cave, protecting the area and part of the aquifer from future development.

“Putting this deal together was no small task,” Nirenberg said at the time. “We worked for more than a year in what sometimes felt like a hopeless situation, but it was the best way to achieve success. This was an interagency public-private partnership that I believe will serve as a model for other communities going forward.”

Backed by contributions from the city of San Antonio, Bexar County, the Edwards Aquifer Authority, the Army and private donors, the Austin-based Nature Conservancy and BCI agreed to purchase the adjacent area, known as Crescent Hills, from Galo Properties.


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