Data collected on juvenile and adult fringe-lipped bats provide the first insights into how eavesdropping behavior develops in these predators.

Scientists at the Smithsonian Tropical Research Institute (STRI) have discovered that fringe-lipped bats, which locate their prey by eavesdropping on frog and toad mating calls, learn to tell the difference between edible and inedible prey through experience.

The findings, published in the Proceedings of the Royal Society B, offer the first evidence that predators who rely on acoustic cues refine their hunting behavior as they develop.

Distinguishing palatable from poisonous

Some predators find food by listening to the sounds their prey make. Fringe-lipped bats, found from Panama to Brazil, are especially skilled at this. They can recognize the mating calls of more than a dozen frog and toad species in their environment and respond within seconds. But not every call leads to a safe meal. Some frogs are too large to handle or produce toxins that can harm the bats.

To manage this risk, fringe-lipped bats seem to have developed a kind of natural caller ID. When they hear a call from a toxic or unpalatable frog, they often ignore it. However, unlike phone calls that come with spam warnings, frog calls offer no clear signals of danger. Until now, it was unclear how these bats learned to make such distinctions.

A fringe-lipped bat, Trachops cirrhosus, responds to the calls of the túngara frog, Engystomops pustulosus, one of its preferred prey species. First, the bat hears the call of a single male túngara frog, producing a complex call (a 'whine' plus multiple 'chucks'.) Then, the bat hears the cacophony of a large túngara frog chorus, with many male túngara frogs acoustically competing for females at once. Credit: Joseph See

"It's truly remarkable that these bats hunt using the calls of an entirely different group of animals in the first place, and we have wondered for a long time how these bats acquire this unusual skill," said Logan James, STRI postdoctoral researcher and lead author of the study. "We knew from previous research that these bats are very clever and can learn during experiments, but we had not tested whether their aptitude for learning had a role in fine-tuning their responses to sound cues from their natural prey."

Juveniles respond differently than adults

The research team tested how individual, wild-caught adult and juvenile fringe-lipped bats responded to mating call recordings of 15 local frog and toad species. These species included frogs known to be palatable, toxic, or too large to handle.

First, the team confirmed previous studies showing that adult bats responded more strongly to palatable versus unpalatable frogs and toads. Yet, as the team discovered, juvenile bats did not make the same distinctions. On average, juvenile bats did not respond differently to frogs and toads based on their palatability.

A fringe-lipped bat, Trachops cirrhosus, hears a male túngara frog, Engystomops pustulosus, producing an advertisement call to attract a mate. The bat approaches the calling frog, but the frog detects it in time, stops calling and ducks, successfully avoiding the eavesdropping predator. Credit: Joseph See

Learning to avoid toxic prey

Looking more closely, the team found that juveniles could identify larger prey by their calls, just like adults can, but they could not distinguish the toxic species. This indicates that juveniles tend to respond to body size early on, but they learn to identify toxic species over time.

"We have studied this fascinating species for years, and in many aspects, we understand its behavior very well," said Rachel Page, staff scientist at STRI, and one of the study's senior authors. "But this was the first time we had ever tested juvenile bats. It was so interesting to see that, like human children, young bats needed time and experience to hone their discrimination skills."

A fringe-lipped bat, Trachops cirrhosus, returns to its perch after a successful hunt, and consumes its prey, a túngara frog, Engystomops pustulosus. Credit: Joseph See

This study is the first to explicitly compare eavesdropping responses of generalist predators at different ages. But it is likely that this strategy is widespread across the animal kingdom, and fringe-lipped bats are not the only predators that need to learn how to distinguish palatable prey. Ultimately, this study highlights the critical role of experience in early life in shaping predatory behaviors in the wild.

"This study highlights the power of development and learning to shape eavesdropping behavior, an insight that may extend far beyond bats to other predators also navigating complex sensory environments," said Ximena Bernal, research associate at STRI, professor at Purdue University and one of the study's senior authors. "We hope it will inspire other scientists to examine how early experience modulates predator-foraging decisions."

Reference: "The ontogeny of decision-making in an eavesdropping predator" by Logan S. James, M. Teague O'Mara, Justin C. Touchon, Michael J. Ryan, Ximena E. Bernal and Rachel A. Page, 31 March 2025, Proceedings B.

DOI: 10.1098/rspb.2025.0450

Funding: Smithsonian Tropical Research Institute, Smithsonian Institution, U.S. National Science Foundation, U.S. National Science Foundation