UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item MOVEMENT ECOLOGY OF THE MEXICAN FISH-EATING BAT, MYOTIS VIVESI(2020) Hurme, Edward; Wilkinson, Gerald S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Foraging behavior is influenced by the distribution of prey in time and space and the presence of conspecifics. Echolocating bats, which advertise their behavior while vocalizing, provide a unique opportunity for understanding how an organism interacts with conspecifics and the environment to find food. Here I use GPS tracking combined with on-board recording to investigate the foraging movements of lactating Mexican fish-eating bats, Myotis vivesi, in the Gulf of California, Mexico, over a 5-year period. In Chapter 1, I assessed five alternative methods for behavioral state segmentation of GPS tracked foraging paths using on-board audio for validation. While most methods perform well, hidden-Markov model segmentation showed the highest accuracy at predicting foraging movement. In Chapter 2, I evaluated habitat selection across multiple scales for fish-eating bats foraging in the Midriff Islands Region in the Gulf of California. Foraging site use at large scales is most predictive and is associated with dynamic (chlorophyll concentration) and static variables (ocean depth, sea floor slope) consistent with known tidal upwelling regions. In Chapter 3, I examine the function of in-flight social calls recorded from roughly half of all tagged individuals during their foraging flights. Calls contained spectral differences among individuals, were associated with the ends of flights as bats return to their roost, and increased in occurrence with pup age, consistent with directive calls used to communicate with mobile pups. In Chapter 4, I explore how prey distribution impacts social behavior and foraging movements. On-board audio reveals that conspecifics are present during commuting and foraging and playback experiments demonstrate an attraction to foraging call sequences. In collaboration with several colleagues I combined these findings with data from four other bat species ranging in diet and habitat type. Taken together, bat species that frequently encounter conspecifics, such as Myotis vivesi, have ephemeral prey and variable flights (e.g. duration and foraging site location), whereas bats that forage solitarily have predictable or non-shareable prey, such as a congener Myotis myotis, show less variability in their flights. Overall, these results provide new insights into the foraging dynamics and social behavior of bats.Item Echolocation, high frequency hearing, and gene expression in the inner ear of bats(2017) Mao, Beatrice; Wilkinson, Gerald S; Moss, Cynthia F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bats are the only mammals capable of true flight, and are the second-most speciose mammalian radiation, represented by over 1200 extant species. Key to their evolutionary success was echolocation, which is a complex trait requiring specializations for vocalization, hearing, and echo processing. Because they rely on detecting and analyzing echoes that may return greatly attenuated relative to their outgoing calls, interference from non-target ‘clutter’ echoes poses a challenge for echolocating bats. Here, I demonstrate that the echolocating bat Eptesicus fuscus alters its echolocation behavior to ameliorate the impact of clutter echoes when tracking a moving target, and that the magnitude of its behavioral adjustments depended on the distance and angular offset of two symmetrically placed ‘distracter’ objects. Furthermore, I found that individual bats make different adjustments to their calls, call timing, or head movements, suggesting that multiple strategies for echolocating in clutter may exist. In my second chapter, I examined the expression patterns of hearing-related genes in juvenile bats. Biomedical research establishing the functional roles of hearing genes rarely examines gene expression beyond the early post-natal stage, even though high frequency hearing does not mature until late in development. I show that several key hearing genes implicated in human deafness are upregulated in juvenile bats relative to adults, or exhibit sustained upregulation through the developmental period corresponding to the maturation of echolocation behavior. In my third chapter, I review the evolution of high frequency hearing in mammals, focusing on echolocating bats and whales, which have independently evolved this complex trait. I provide an overview of recent studies that have reported molecular convergence in hearing genes among distantly related echolocators, and assert that the contribution of gene expression to hearing deserves further investigation. Finally, I argue that echolocators provide a unique opportunity to investigate the basis of high frequency amplification, and may possess mechanisms of hearing protection which enable them to prolong the use of echolocation throughout their long lives.Item ADAPTIVE FLIGHT AND ECHOLOCATION BEHAVIOR IN BATS(2015) Falk, Ben; Moss, Cynthia F; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bats use sonar to identify and localize objects as they fly and navigate in the dark. They actively adjust the timing, intensity, and frequency content of their sonar signals in response to task demands. They also control the directional characteristics of their sonar vocalizations with respect to objects in the environment. Bats demonstrate highly maneuverable and agile flight, producing high turn rates and abrupt changes in speed, as they travel through the air to capture insects and avoid obstacles. Bats face the challenge of coordinating flight kinematics with sonar behavior, as they adapt to meet the varied demands of their environment. This thesis includes three studies, one on the comparison of flight and echolocation behavior between an open space and a complex environment, one on the coordination of flight and echolocation behavior during climbing and turning, and one on the flight kinematic changes that occur under wind gust conditions. In the first study, we found that bats adapt the structure of the sonar signals, temporal patterning, and flight speed in response to a change in their environment. We also found that flight stereotypy developed over time in the more complex environment, but not to the extent expected from previous studies of non-foraging bats. We found that the sonar beam aim of the bats predicted flight turn rate, and that the relationship changed as the bats reacted to the obstacles. In the second study, we characterized the coordination of flight and sonar behavior as bats made a steep climb and sharp turns while they navigated a net obstacle. We found the coordinated production of sonar pulses with the wingbeat phase became altered during navigation of tight turns. In the third study, we found that bats adapt wing kinematics to perform under wind gust conditions. By characterizing flight and sonar behaviors in an insectivorous bat species, we find evidence for tight coordination of sensory and motor systems for obstacle navigation and insect capture. Through these studies, we learn about the mechanisms by which mammals and other organisms process sensory information to adapt their behaviors.Item Estimation of Elevation and Azimuth in a Neuromorphic VLSI Bat Echolocation System(2009) Abdalla, Hisham Ahmed Nabil; Horiuchi, Timothy K; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Auditory localization is an interesting and challenging problem; the location of the sound source is not spatially encoded in the peripheral sensory system as it is in the visual or somatosensory systems. Instead it must be computed from the neural representation of the sound reaching both ears. Echolocation is a form of auditory localization, however, an important distinction is that the sound being localized is an echo of the sound emitted by the animal itself. This dissertation presents a neuromorphic VLSI circuit model of a bat echolocation system. The acoustic cues that we use in our system are the binaural interaural level differences (ILDs) and the monaural spectral cues. We have designed an artificial bat head using 3D CAD software and fabricated it using a 3D printer. The artificial bat head is capable of generating the necessary acoustic cues for localization. We have designed and fabricated an ultrasonic cochlea chip with 16 cochlear filters and 128 spiking cochlear neurons (eight neurons per cochlear filter), the cochlear filters and neurons transform the analog input into a spike-based cochlear representation. We have also designed and fabricated two feature extraction chips: a monaural spectral difference chip and a binaural ILD chip, that together can extract the localization cues from the spike-based cochlear representation. The monaural spectral difference chip consists of 240 spiking neurons; each neuron compares the activity of two cochlear filters within the same ear. The binaural ILD chip consists of 32 spiking neurons (two per cochlear filter) that model the processing that takes place in the lateral superior olive (LSO). We demonstrate that the spatiotemporal pattern of spiking outputs from the feature extraction chips can be decoded to estimate the direction (elevation and azimuth) of an ultrasonic chirp.Item Sound Localization by Echolocating Bats(2007-05-14) Aytekin, Murat; Moss, Cynthia F.; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Echolocating bats emit ultrasonic vocalizations and listen to echoes reflected back from objects in the path of the sound beam to build a spatial representation of their surroundings. Important to understanding the representation of space through echolocation are detailed studies of the cues used for localization, the sonar emission patterns and how this information is assembled. This thesis includes three studies, one on the directional properties of the sonar receiver, one on the directional properties of the sonar transmitter, and a model that demonstrates the role of action in building a representation of auditory space. The general importance of this work to a broader understanding of spatial localization is discussed. Investigations of the directional properties of the sonar receiver reveal that interaural level difference and monaural spectral notch cues are both dependent on sound source azimuth and elevation. This redundancy allows flexibility that an echolocating bat may need when coping with complex computational demands for sound localization. Using a novel method to measure bat sonar emission patterns from freely behaving bats, I show that the sonar beam shape varies between vocalizations. Consequently, the auditory system of a bat may need to adapt its computations to accurately localize objects using changing acoustic inputs. Extra-auditory signals that carry information about pinna position and beam shape are required for auditory localization of sound sources. The auditory system must learn associations between extra-auditory signals and acoustic spatial cues. Furthermore, the auditory system must adapt to changes in acoustic input that occur with changes in pinna position and vocalization parameters. These demands on the nervous system suggest that sound localization is achieved through the interaction of behavioral control and acoustic inputs. A sensorimotor model demonstrates how an organism can learn space through auditory-motor contingencies. The model also reveals how different aspects of sound localization, such as experience-dependent acquisition, adaptation, and extra-auditory influences, can be brought together under a comprehensive framework. This thesis presents a foundation for understanding the representation of auditory space that builds upon acoustic cues, motor control, and learning dynamic associations between action and auditory inputs.