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1. Auditory Communication Processing in Bats: What We Know and Where to Go

   https://doi.org/http://dx.doi.org/10.1037/bne0000308  

   Salles, A.; Bohn, K.; Moss, C.F. (June 2019, Behavioral neuroscience)

   Bats are the second largest mammalian order, with over 1,300 species. These animals show diverse behaviors, diets, and habitats. Most bats produce ultrasonic vocalizations and perceive their environment by processing information carried by returning echoes of their calls. Echolocation is achieved through a sophisticated audio-vocal system that allows bats to emit and detect frequencies that can range from ten to hundreds of kilohertz. In addition, most bat species are gregarious, and produce social communication calls that vary in complexity, form, and function across species. In this article, we (a) highlight the value of bats as model species for research on social communication, (b) review behavioral and neurophysiological studies of bat acoustic communication signal production and processing, and (c) discuss important directions for future research in this field. We propose that comparative studies of bat acoustic communication can provide new insights into sound processing and vocal learning across the animal kingdom. 

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2. Sound evoked Fos-like immunoreactivity in the big brown bat

   https://doi.org/10.1016/j.ibneur.2022.02.005  

   Salles, A. (January 2022, IBRO neuroscience reports)

   Most bat species have highly developed audio-vocal systems, which allow them to adjust the features of echolocation calls that are optimized for different sonar tasks, such as detecting, localizing, discriminating and tracking targets. Furthermore, bats can also produce a wide array of social calls to communicate with conspecifics. The acoustic properties of some social calls differ only subtly from echolocation calls, yet bats have the ability to distinguish them and reliably produce appropriate behavioral responses. Little is known about the underlying neural processes that enable the correct classification of bat social communication sounds. One approach to this question is to identify the brain regions that are involved in the processing of sounds that carry behavioral relevance. Here, we present preliminary data on neuronal activation, as measured by c-fos expression, in big brown bats (Eptesicus fuscus) exposed to either social calls, echolocation calls or kept in silence. We focused our investigation on five relevant brain areas; three within the canonical auditory pathway (auditory cortex, inferior colliculus and medial geniculate body) and two that are involved in the processing of emotive stimulus content (amygdala and nucleus accumbens). In this manuscript we report c-fos staining of the areas of interest after exposure to conspecific calls. We discuss future work designed to overcome experimental limitations and explore whether c-fos staining reveals anatomical segregation of neurons activated by echolocation and social call call categories. 

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3. Neural Response Selectivity to Natural Sounds in the Bat Midbrain

   https://doi.org/10.1016/j.neuroscience.2019.11.047  

   Salles, A.; Park, S.; Sundar, H.; Macias, S.; Elhilali, M.; Moss, C.F. (May 2020, Neuroscience)

   Little is known about the neural mechanisms that mediate differential action–selection responses to communication and echolocation calls in bats. For example, in the big brown bat, frequency modulated (FM) food-claiming communication calls closely resemble FM echolocation calls, which guide social and orienting behaviors, respectively. Using advanced signal processing methods, we identified fine differences in temporal structure of these natural sounds that appear key to auditory discrimination and behavioral decisions. We recorded extracellular potentials from single neurons in the midbrain inferior colliculus (IC) of passively listening animals, and compared responses to playbacks of acoustic signals used by bats for social communication and echolocation. We combined information obtained from spike number and spike triggered averages (STA) to reveal a robust classification of neuron selectivity for communication or echolocation calls. These data highlight the importance of temporal acoustic structure for differentiating echolocation and food-claiming social calls and point to general mechanisms of natural sound processing across species. 

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4. Effects of Environmental Clutter on Synthesized Chiropteran Echolocation Signals in an Anechoic Chamber

   https://doi.org/10.3390/acoustics3020026  

   Freeze, Samuel R.; Shirazi, Masoud; Abaid, Nicole; Ford, Mark; Silvis, Alexander; Hakkenberg, Dawn (June 2021, Acoustics)

   Ultrasonic bat detectors are useful for research and monitoring purposes to assess occupancy and relative activity of bat communities. Environmental “clutter” such as tree boles and foliage can affect the recording quality and identification of bat echolocation calls collected using ultrasonic detectors. It can also affect the transmission of calls and recognition by bats when using acoustic lure devices to attract bats to mist-nets. Bat detectors are often placed in forests, yet automatic identification programs are trained on call libraries using echolocation passes recorded largely from open spaces. Research indicates that using clutter-recorded calls can increase classification accuracy for some bat species and decrease accuracy for others, but a detailed understanding of how clutter impacts the recording and identification of echolocation calls remains elusive. To clarify this, we experimentally investigated how two measures of clutter (i.e., total basal area and number of stems of simulated woody growth, as well as recording angle) affected the recording and classification of a synthesized echolocation signal under controlled conditions in an anechoic chamber. Recording angle (i.e., receiver position relative to emitter) significantly influenced the probability of correct classification and differed significantly for many of the call parameters measured. The probability of recording echo pulses was also a function of clutter but only for the detector angle at 0° from the emitter that could receive deflected pulses. Overall, the two clutter metrics were overshadowed by proximity and angle of the receiver to the sound source but some deviations from the synthesized call in terms of maximum, minimum, and mean frequency parameters were observed. Results from our work may aid efforts to better understand underlying environmental conditions that produce false-positive and -negative identifications for bat species of interest and how this could be used to adjust survey accuracy estimates. Our results also help pave the way for future research into the development of acoustic lure technology by exploring the effects of environmental clutter on ultrasound transmission. 

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5. Transfer Entropy Analysis of Interactions between Bats Using Position and Echolocation Data

   https://doi.org/10.3390/e22101176  

   Shaffer, Irena; Abaid, Nicole (October 2020, Entropy)

   null (Ed.)

   Many animal species, including many species of bats, exhibit collective behavior where groups of individuals coordinate their motion. Bats are unique among these animals in that they use the active sensing mechanism of echolocation as their primary means of navigation. Due to their use of echolocation in large groups, bats run the risk of signal interference from sonar jamming. However, several species of bats have developed strategies to prevent interference, which may lead to different behavior when flying with conspecifics than when flying alone. This study seeks to explore the role of this acoustic sensing on the behavior of bat pairs flying together. Field data from a maternity colony of gray bats (Myotis grisescens) were collected using an array of cameras and microphones. These data were analyzed using the information theoretic measure of transfer entropy in order to quantify the interaction between pairs of bats and to determine the effect echolocation calls have on this interaction. This study expands on previous work that only computed information theoretic measures on the 3D position of bats without echolocation calls or that looked at the echolocation calls without using information theoretic analyses. Results show that there is evidence of information transfer between bats flying in pairs when time series for the speed of the bats and their turning behavior are used in the analysis. Unidirectional information transfer was found in some subsets of the data which could be evidence of a leader–follower interaction. 

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