Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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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.