Acoustical Society of America
158th Meeting Lay Language Papers
Emotion‑related Acoustic Communication in Bats
Sabine Schmidt - sabine.schmidt@iho-hannover.edu
Institute of Zoology
University of Veterinary Medicine Hanover
Buenteweg17
30559 Hannover, Germany
Popular version of paper 2pAB1
Presented Tuesday afternoon Oct 27, 2009
158th ASA meeting San Antonio, TX
Most pet holders will happily admit that their dogs or cats are able to express different emotional states in their barking or meowing. From an animal bioacoustics point of view and from an evolutionary perspective, however, this statement provokes a variety of questions. Are mammals in general able to express their emotions during social interactions in their voices? And, if so, is the emotion carried by a universal code that can be even understood across species (so that an owner intuitively understands his dog's needs)?
Have animals already developed the ability to read the emotional state in the calls of their conspecific interaction partners? And is this ability common to mammals or limited to primates, our closer relatives?
We studied the role of vocal communication of emotions in bats, a highly vocal group evolutionarily remote from primates. Our experiments revealed that bats not only express emotional states in their vocalizations but also evaluate playbacks of social calls of their conspecifics. This suggests that even mammals remote from apes and humans are able to read the emotional state in vocal expressions.
The focus of the present paper is on vocal communication during agonistic interactions in the Indian False Vampire bat, Megaderma lyra.
In a first experiment, we studied vocal expression during agonistic interactions between two bats: a perching bat and an approaching bat that wants to sit at the same perch
WATCH a video of a weak aggressive display.
We rated the intensity of the agonistic interaction from the video and independently performed a sound analysis of the scenes. Then we analyzed whether the call parameters differed significantly between situations with weak and strong agonistic interactions. We found that the call type indicated the specific part of the respective caller: typically, the perch holding bat emitted an aggression call towards the approaching bat, which in turn responded with a response call.
LISTEN to the aggressive call and the reponse.
Moreover, the intensity of the interaction, as rated by us by the videos, was encoded in systematic changes of the call parameters, and these changes were similar for both call types. Interestingly, these changes corresponded to those found in human speech: for example, syllable repetition rates increased with aggression level, such as in humans which tend to speak faster in the corresponding situation.
In a second experiment, we investigated whether the bats could read vocalizations emitted during interactions of two other bats without being directly involved in it. To address this question, we played back calls from agonistic interactions via a loudspeaker to a bat that was waiting for prey at its feeding perch. Initially, the bats would turn towards the sound source; when, however, calls from the same call category were repeatedly played back to the bats, they quickly lost interest, i.e. they habituated to the calls and did not react at all. If we then played a stimulus of the second category, two fundamentally different responses did occur, depending on which call category had been used for habituation: if, for example, a response call followed a series of aggression calls, the bats would be interested and turn towards the sound source again. If, on the other hand, an aggression call followed a series of response calls, the bats did not react. This shows that bats - beyond a mere discrimination of call categories - are able to evaluate or rate social calls according to some higher-level rules dependent on the context in which they are
emitted.
Our experiments suggest that emotional processes are not only mapped onto bat vocal expressions, but that vocal expressions ‑ even if isolated from the normal behavioral display ‑ also mediate the responses of listening bats. A closer look at this exotic group of mammals may indeed help to better understand the roots of human vocal communication.