Hearing in Bats

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DESCRIPTION (provided by applicant): The long-range goals of this project are to determine the ecological and morphological correlates of the variation in hearing abilities of mammals and to examine the role of vision in the evolution of hearing. It continues our comparative approach to explore the wide range of hearing abilities in bats. Bats present an opportunity to discover any effects that the auditory specialization for echolocation may have had on basic mammalian auditory abilities. The proposed project is a comparative survey of hearing in Common Vampire bats (Desmodus rotundus). Vampires are a pest in the tropics of this hemisphere and a serious health hazard to humans and especially to their livestock. They can cause severe blood loss in livestock because they tend to feed repeatedly from the same individual; they also are vectors for disease. Understanding how Vampires use sound to find and identify prey may help guide efforts at control. Vampires are medium-sized bats that use low-intensity FM echolocation signals to seek prey against a cluttered substrate. Unlike most bats, they depend heavily on passive listening to detect prey. They may thus be under heavier selective pressure for good sound localization acuity, perhaps taking advantage of the highly developed echolocation mechanisms to enhance passive localization. They may also be somewhat sensitive to low-frequency sounds, including the breathing sounds of their prey, which, if true, suggests a versatile middle ear and cochlear mechanism for encoding sound. We will use behavioral tests methods to determine 1) absolute sensitivity throughout the hearing range, 2) the ability to detect very brief sounds and very brief gaps in sound, since echolocation pulses are usually very short (<5 ms) and separated by very brief intervals, 3) passive sound-localization acuity, 4) the ability to use interaural time and intensity difference cues for locus, and 5) the relation of sound-localization to vision, since bats vary in their reliance on vision. In addition we will 6) examine the detectability of biologically relevant sounds, including human breathing sounds and communication calls of vampire pups. The spectra of these sounds will be compared to the frequency range and best sensitivity of the adult audiogram (with behavioral detection thresholds for biological sounds obtained as appropriate). The ultimate goal of this research is to further our understanding of neural processing in the auditory system to gain perspective on human hearing. In addition, we will gain insight into how the interaction of the senses in different lifestyles has influenced the evolution of perceptual adaptations and the neural substrates underlying those adaptations. Vampire bats are a direct health hazard for humans and their livestock in the tropical regions of this hemisphere. They are also carriers of serious disease. This project will help understand how vampires detect, locate, and identify their prey for better management of safety of livestock.