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Eavesdropping fringe-lipped bats spread culture through sound

June 20, 2006

AUSTIN, Texas—Like a diner ordering a dessert based solely on the "oohs" and "aahs" of a customer eating the same dish the next table over, frog-eating bats learn to eat new prey by eavesdropping on their neighbors as they eat, report biologists from The University of Texas at Austin.

Rachel Page and Mike Ryan, studying fringe-lipped bats at the Smithsonian Tropical Research Institute on Barro Colorado Island in Panama, found that naÃ-ve bats quickly learned to associate a new frog call with edible prey by observing their neighbor eating, even when the call comes from a frog they wouldn't normally eat.

Page, a graduate student in Ecology, Evolution and Behavior, and Ryan, the Clark Hubbs Regents Professor in Zoology, report their findings in the June 20 issue of Current Biology.

This is the first study to show predators learning socially through acoustic, rather than visual or olfactory, prey cues.

"It is stunning that these bats show such rapid changes in their responses to prey cues, to the extent that they will respond to a stimulus that they should be under strong selective pressure to avoid in the wild," said Page. "This result is very unexpected and shows an extreme degree of flexibility."

Through the bats' ability to learn socially, the new connection between a frog call and the presence of food can quickly spread through the tight-knit bat colony.

To observe the cultural transmission of this new information in the bats, Page and Ryan captured wild fringe-lipped bats and tested them in large outdoor flight cages. They played the calls of large, poisonous cane toads through speakers and gave the bats that approached the speaker a reward of raw fish. Once a bat learned to associate the cane toad call with food, they became "tutor" bats.

NaÃ-ve bats were then allowed to observe the tutor bats. The naÃ-ve bats, on average, learned to associate the new frog call with food after observing their tutor five times. Page and Ryan believe the naÃ-ve bat observes the tutor's location through echolocation and then listens to it chewing on its prey.

"There have been many of studies on diet and learning, but most have been conducted with laboratory animals," said Page. "This study is exciting because we are taking wild bats, bringing them into an outdoor flight cage and within a matter of days observing social learning and innovative foraging behavior."

Page and Ryan suggest that major switches in the bats' diet can take place rapidly and without trial-and-error learning through their ability to learn socially. As frog species decline and change in tropical areas, the fringe-lipped bats' social learning skills could be an advantage.

"This study has interesting conservation implications," said Page. "For a predator that is specialized to feed on a group of animals facing catastrophic extinctions (for example, frogs), it is important to know what type of response these bats might show to drastic changes in prey abundance and composition. Our study suggests that at least in terms of foraging ecology, frog-eating bats could rapidly track fluctuations in the prey community."

Future studies will look at how the fringe-lipped bat responds to all 28 of the frog species present on Barro Colorado Island.

University of Texas at Austin