Meant to help bats, these devices may actually turn them away

Pipes allowing bats entrance into caves may distort sound and deter them from entering

In an effort to keep people out of dangerous caves and mines, managers often put up gates or grills at the entrances. But to allow bats to access their roosts, they often add pipes for them to fly through.

Researchers recently found those pipes — which often have corrugated rings for added strength — may actually interfere with bat echolocation.

Scientists had already noticed that caves or mines with these types of pipes were deterring bats from going into their roosts. “We figured there must be some characteristic of the pipes that was causing a problem,” said James Simmons, a professor in the department of neuroscience at Brown University who led the study published in Scientific Reports.

The researchers used a 6-by-3-meter flight room to test out how big brown bats (Eptesicus fuscus) may be affected by the pipes. In the narrow room, they hung plastic chains to model vegetation. And because corrugated pipes were too heavy and large to carry into the room, the team used a row of hula hoops, mimicking the pipes, for the bats to fly through to determine if it affected bats behavior and echolocation.

Simmons and his colleagues used microphones and video cameras and chased the bats as they flew while recording their sounds. They noted whether or not the bats successfully reached their destination when the hula hoops were present versus when they weren’t.

“If the hula hoops were there, the bats did not go along the tunnel,” he said. “They flew away from the hula hoops.” In fact, the bats only conducted half of the flights when the hula hoops were present than if just the chains were up.

When the researchers compared the bats’ echolocation patterns during flights through the hoops with those when just the chains were present, they found the bats emitted different echolocation patterns as well. The bats emitted more rapid sound pulses while going through the hoops. Past research suggests this means it was a more difficult task cognitively.

Certain bats emit different timing patterns in their sonar, Simmons said, but the hula hoop task was so difficult, the team couldn’t tell the difference between the bats through their sounds. This change in patterns, he said, could also make it difficult for bats to tell one another apart, and they can interfere with one another.

With dangerous, abandoned mines scattered throughout the West, it’s important to deter people from going into them Simmons said, but managers don’t want to block them, especially because some bat populations are threatened or endangered.

The researchers suggest that managers can address the issue by spraying concrete over the corrugations inside the pipes. This could reduce the acoustic distortions that cause the echolocation concerns, he said.