Studies On The Vocal Adjustment Ability Of Constant Frequency-Frequency Modulation Bats Under Different Acoustic Environments

Facing with the widespread acoustic interference in environment,animals exhibit flexible vocal behavior to facilitate acoustic communication.Echolocating bats are highly dependent on acoustic signals to communicate,locate,and foraging in darkness.And most of them are highly social,so,acoustic interference is a daily occurrence for them.As the “auditory specialist”,but previous studies have been limited to call level,so it’s not clear that echolocating bats have the ability to fine-tune vocalizations on a much smaller time scale as humans.In addition,echolocating bats use echoes they receive to sense the environment,but the audio-vocal feedback is also essential for their vocal processing.However,we still unclear the auditory pathway that the basis of auditory feedback for the adjustment of echolocating bats’ vocal behavior under noise interference.While,sound in the environment may not always pose adverse effects,it depends on the situation of animals and how they react.In addition to the widespread acoustic interference in the environment,as the highly social animal,calls from other bats in their environment are also an acoustic challenge.Previous studies have suggested that echolocating bats exhibit “Jamming of avoidance response” in order to reduce the overlap with other bats’ sonar signals,but some studies also suggested that echolocating bats can distinguish their identity based on their baseline differences among individuals,so they do not need to adjust their sonar signals.But we still don’t know how echolocating bats adjust their sonar behavior in response to others.And some studies show that the echolocation calls have the potential for social communication.Therefore,in order to make sure the vocal behavior of echolocating bats in different acoustic environments and the pathway of auditory feedback,this study attempts to expand from the aspects of acoustic environment situation and bat state,to get a deeper understanding of the adjustment ability and significance of bat’s sonar system.Human and vertebrates will unconsciously increase their vocal amplitude in noise,the Lombard effect,one of the most efficient way to compensate for the deteriorated signal-to-noise ratio(SNR).Previous studies on the Lombard effect in humans have suggested that people can help improve intelligibility by compensating for differences in vocal intensity at the syllable level,but such fine control has not been found in other animals.For the Constant Frequency-Frequency Modulation(CF-FM)bat,their echolocation call consists of two distinct components,CF part and FM part,which resemble the different syllables of the words in human language.Therefore,we explored the vocal behavior of CF-FM bats exposed to white noise.Results showed that ambient noise induced a strong,but differential Lombard effect in the CF and FM components of the echolocation calls,so echolocating bats adjust their echolocation call at the syllable-level as humans do.But further results showed that the behavior of intensity differentiation compensation at different component levels only existed when the noise overlapped with the dominant frequency of the bat’s vocalization,suggesting a functional role in releasing masking.Echolocating bats sense environment through the echoes they receive,but audio-vocal feedback,which is widely available in mammals,and also involved in bats’ vocalizations adjustment.However,it is unclear the auditory pathway that echolocating bats change their vocal behavior induced by noise are based on audio-vocal feedback or echo feedback.In order to investigate the role of echo feedback and audio-vocal feedback in echolocating bats,we quantified the vocal behavior of echolocating bats during a landing task to answer it.And results showed that echolocating bats exhibited an obvious echo level compensation behavior during landing task,and the closer the distance,the higher the slope of the echo intensity compensation.However,broadcasts delayed the rate of echo level compensation.By analyzing the variation of echolocation calls at different distance windows,results showed that the increasement of call level was inconsistent during landing: the increase of the call level at the distant window was often more than that at the close window.And similar patterns were also found in the duration of different components of the call.These data suggest that noise-induced vocal modifications in echolocating bats relying on echo feedback,indicating a different mechanism from non-echolocating animals.In addition to the widespread noise in the environment,calls from other individuals may also pose an interfere for bats’ acoustic communication,but studies show that these calls carry key information for social communication as social calls.However,until now,how bats use echolocation calls for acoustic communication has remained unclear.To make sure the influence of sonar signals from other individuals on bats’ echolocation calls,we explored by pairing and playback.The results showed that echolocating bats would raise their call frequency in response to conspecifics,and the greater the difference in baseline call frequency of the pairs,the more their call frequency would increase,and keep the difference in call frequency stable,that is,there was no “jamming of avoidance response”.In addition,when we simulated the echolocation calls of other individuals by playback,results showed that when the frequency of echolocation calls played back was consistent with that of echolocating bats,they would increase their call frequency as previously,and as playback stopped,the frequency of the call decreased and returned to the original level gradually.When the frequency of the calls played back was significantly higher or lower than that of the echolocating bats,they raised or lowered the call frequency in line with the direction of the playback,and gradually returned to the original level once the playback was over.The response of echolocating bats to echolocation signals from different bat groups we stimulated is based on real-time auditory information,but for them,there seems to be an “acoustic barrier” that limits their response.In conclusion,we explore the sonar behavior of echolocating bats by building experimental platforms,such as microphones arrays and playback systems,and the technological means of programmed automatic control and playback simulation.The present data demonstrates that the fine-tuned vocal adjustment of echolocating bats and the pathway of auditory feedback basis on which noise-induced acoustic behavior is adjusted.The flexible vocal behavior of echolocating bats contributes to our understanding of the behavior and mechanisms of mammalians,as well as the differences in noise-induced vocal regulation between echolocation and non-echolocation animals.In addition,this paper also provides key experimental evidence for the acoustic communication of echolocation calls,which does lay a foundation for further understanding the vocal learning ability of bats’ sonar signal.