The Echolocation Adjustment Strategy Of Hipposideros Armiger In Response To Changes In Temperature And Humidity

Active sensing refers to an important skill of organisms that use external sensory organs such as vision,hearing,and smell to collect,monitor,and adjust signals to perceive the environment.Acoustic signals are widely used by animals for social communication,spatial orientation and foraging,and serve as an important information carrier for maintaining animal population stability and community balance.Acoustic signals in animals are easily affected by environmental factors during sound propagation in the air due to atmospheric attenuation(i.e.,the reduction in sound amplitude caused by absorption of acoustic energy by the air molecules and other effects).The atmospheric attenuation impairs the reception of signals for the signal receiver.In many animals,reducing the loss of acoustic signals in the environment is a way to improve their habitat suitability.Consequently,animal acoustic signals can be an ideal model for the study of regulatory behavior of animals in response to environmental changes,and provide a new perspective for disentangling the adaptive evolutionary mechanism of animal perception systems.The echolocation behavior of bats is a typical form of acoustic active perception.High-frequency echolocation calls improve the spatial accuracy of detection in bats,conferring them the ability to detect tiny insects.High-frequency echolocation calls,however,are more likely to suffer from atmospheric attenuation,especially under warm and moist conditions.The constant-frequency(CF-FM)bats evolved advanced echolocation systems that employ CF-FM calls for spatial orientation and prey seeking in complex forest habitats through special Doppler shift compensation.To date,it is still unclear whether CF-FM bats adjust temporal-spectrum parameters of echolocation calls during flight to deal with the atmospheric attenuation caused by temperature and humidity changes.Less is known about whether changes in environmental conditions affect Doppler shift compensation in CF-FM bats.To fill these gaps,we used Hipposideros armiger to assess the adjustment strategy of echolocation in response to changes in ambient temperature and humidity.Using the advanced microphone array acquisition and high-speed camera tracking systems,we simultaneously recorded echolocation and flight behavior of H.armiger under different temperature and humidity combinations in the laboratory,where environmental temperature and humidity can be precisely controlled.The specific research results are as follows:(1)The average flight speed of H.armiger ranged from 3.49 to 5.18 m/s,with an average of 4.47 ± 0.31 m/s.In each flight experiment,the speed of H.armiger during flight showed a downward trend as their distance to the window declined.Despite a marked individual difference,flight speed of experimental bats differed between different gradient combinations of temperature and humidity(?2 = 104.8,P < 0.001).(2)There were significant differences in the atmospheric attenuation of echolocation calls under different temperature and humidity conditions,and the atmospheric attenuation of echolocation calls increased with the rise of temperature and humidity.Both the resting frequency and the peak frequency of the echolocation calls during the resting and flight of bats decreased significantly with the increase of the atmospheric attenuation.Atmospheric attenuation is an important source of signal attenuation for bats using high frequency echolocation calls.(3)The resting frequency,peak frequency during flight and the bandwidth of the CF component of H.armiger showed a significant shift when environmental temperature changed(P < 0.01),and were significantly affected by temperature(P <0.001)but the influence of humidity changes was not significant.The pulse duration of H.armiger was also significantly different under different combinations of temperature and humidity(?2 = 32.381,P < 0.001).The duration of three individuals among the five individuals varies with the changes in the combination of temperature and humidity were not significant,and the changes in the duration of two individual were related to the changes in body temperature under different temperature and humidity.(4)The DSC precision in H.armiger was 0.137 ± 0.031%,which was significantly different under different temperatures and humidity(?2 = 57.123,P < 0.001),and with the increase of atmospheric attenuation,DSC was more accurate.There were individual differences in offset between reference frequency and resting frequency which did not change with changes in temperature and humidity.Temperature and humidity can cause adjustments of DSC in H.armiger.Collectively,these results suggest that atmospheric attenuation is an important source of echolocation signal attenuation for H.armiger owing to the use of highfrequency ultrasonic calls.H.armiger can actively adjust echolocation call parameters to compensate for effects of atmospheric attenuation according to changes in environmental temperature and humidity.Our findings highlight the adaptive adjustment of echolocation call design under different temperature and humidity conditions,and provide evidence in support of the influence of temperature and humidity on DSC precision in CF bats.Our findings broaden our understanding of the plasticity and adaptive mechanism of active perception system in bats under environmental changes,providing a scientific basis for predicting the impact of global climate warming on animal behavior and associated environmental adaptation.