AUSTIN (KXAN) — The species of bats that call the Congress Avenue bridge home can become infected with the virus that causes COVID-19, but they don’t become sick or spread it, according to a study by the U.S. Geological Survey.

The study, released Tuesday, took 10 Mexican free-tailed bats — the species famous for taking flight from underneath the bridge in the spring and fall months — and monitored their health after they were exposed to the virus. Half of them tested positive for 6-18 days, the study said, but “none of the infected bats showed signs of illness and there was no evidence that they spread the virus to healthy bats in shared enclosures.”

About 1.5 million Mexican free-tailed bats call the underside of the bridge home, and the USGS said the bats, “contribute to healthy ecosystems, and they provide critical agricultural services by eating a large number of insect pests every night.”

The study suggests that COVID-19 isn’t deadly to this specific species of bats, but the USGS said more research needs to be done to, “understand potential impacts of this virus on wildlife should it be detected in wild Mexican free-tailed bats or in other North American bat species.”

The USGS said the study was done due to concerns that humans could inadvertently spread COVID-19 to bats during research or rehabilitation.

“As the virus that causes COVID-19 continues to circulate, our study addresses its potential to infect native wildlife populations,” said Jeffrey Hall, a USGS scientist and lead author of the study. “The findings can help managers understand the risk this virus poses to valuable Mexican free-tailed bats.”