Effects Of Bandwidth Of Noise On Echolocation Signals Of Hipposideros Pratti During A Landing Task

Background: The active sensing system of echolocation enables bats to carry out a variety of activities in a complex and diverse environments.The echolocation calls of bats are extremely flexible,which is evidenced by the observations that bats modify parameters of echolocation signals based on the complexity of the environment in difficult tasks such as obstacle avoidance,target ranging and detection.Noise is ubiquitous in nature,and it affects many aspects of animal life.Noise can be practically categorized into wide band or narrowband based on the energy distribution across the frequency range.Several studies have investigated the effects of noise on acoustic structure and behavior during echolocation in bats,yet the bandwidth of noise,particularly the effect of 1 k Hz bandwidth noise on echolocation in bats,have not been explored.In this thesis,the characteristics of echolocation calls of Hipposideros pratti during a landing task were measured under the conditions of broadband and narrowband noise.Methods: In this experiment,bat individuals were first trained to fly and land on a meshed net.Afterwards,the echolocation calls of the bat during the landing task were recorded with a miniature onboard microphone and a microphone array,when the bats were exposed to different types of bandpass filtered white noise.Then,through statistical analysis of all flight events of a single bat and multiple bats using linear models and linear mixed models,the comparison of different parameters of the second harmonic of echolocation calls of flying bats is conducted.Results: The microphone array data show that the dominant frequency of echolocation of the bats plays an important role in affecting their vocal responses in noise,including the Lombard effect.Clear Lombard effect was observed when the noise interferes with the first or third harmonics of echolocation call of the flying bats,as well as the second harmonic of the calls,but not in the 1 k Hz narrow bandwidth noise conditions.Under medium and broad bandwidth noise interference,the accuracy of the constant frequency component of the second harmonic of the call of Hipposideros pratti(CF-FM bat)is superior to the frequency modulated component.Narrow bandwidth noise has a greater impact on constant frequency component of the second harmonic of the call in flying bats compared to the medium and broad bandwidth noise.Producing calls of longer duration and broader bandwidth can be helpful for flying bats to cope with noise interference,especially when the noise interferes with the dominant frequencies of the calls.In the face of 1 k Hz narrow bandwidth noise,bats increase bandwidth and duration.On-board microphone data show that noise that interferes with the the harmonic with main energy of echolocation calls affects the bat’s Doppler shift compensation performance.Conclusion: Bats can adopt different acoustic strategies to deal with different types of noise interference during the landing task.This allows bats to flexibly use echolocation to overcome interference in challenging environments.This study shows that the bandwidth of the noise is a key factor affecting the Lombard effect in bats and reveals the vulnerability of Doppler shift compensation of flying bats to noise interference.