Bats can understand the emotional state of other bats from the intonations of their calls, a new study suggests. In the lab, researchers observed greater false vampire bats (Megaderma lyra, pictured) that had been trained to wait for food on a perch. In some tests, they played “aggression calls” over a speaker, typically made by a bat defending its place on a perch from an approaching bat. In other trials, the researchers played “appeasement calls” often made by a bat approaching one already ensconced on a perch and thus seeking to share its space. (Bats were tested individually, and the use of recorded calls ensured that the bats were responding to the content of the call and not visual cues from another bat.) In all tests, the scientists played a call once every 20 seconds until the bats began to ignore the call (by not turning toward the speaker), and then they played a slightly different version of the same call—one that was either more urgent (with shorter, more closely spaced syllables) or less urgent. The novel aggression calls always caused a bat to turn toward the speaker, but the novel appeasement calls only drew a response when they became more urgent, the researchers report online today in Frontiers of Zoology. The failure of a bat to react to weakening appeasement calls suggests that the bats can interpret the emotional content of the calls—a sign that such perception might exist more widely in mammals than previously thought.
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