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Pedersen MB, Beedholm K, Hubancheva A, Koseva K, Uebel AS, Hochradel K, Madsen PT, Stidsholt L. Clutter resilience via auditory stream segregation in echolocating greater mouse-eared bats. J Exp Biol 2024; 227:jeb246889. [PMID: 38841890 DOI: 10.1242/jeb.246889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Accepted: 05/21/2024] [Indexed: 06/07/2024]
Abstract
Bats use echolocation to navigate and hunt in darkness, and must in that process segregate target echoes from unwanted clutter echoes. Bats may do this by approaching a target at steep angles relative to the plane of the background, utilizing their directional transmission and receiving systems to minimize clutter from background objects, but it remains unknown how bats negotiate clutter that cannot be spatially avoided. Here, we tested the hypothesis that when movement no longer offers spatial release, echolocating bats mitigate clutter by calling at lower source levels and longer call intervals to ease auditory streaming. We trained five greater mouse-eared bats (Myotis myotis) to land on a spherical loudspeaker with two microphones attached. We used a phantom-echo setup, where the loudspeaker/target transmitted phantom clutter echoes by playing back the bats' own calls at time delays of 1, 3 and 5 ms with a virtual target strength 7 dB higher than the physical target. We show that the bats successfully landed on the target, irrespective of the clutter echo delays. Rather than decreasing their source levels, the bats used similar source level distributions in clutter and control trials. Similarly, the bats did not increase their call intervals, but instead used the same distribution of call intervals across control and clutter trials. These observations reject our hypothesis, leading us to conclude that bats display great resilience to clutter via short auditory integration times and acute auditory stream segregation rather than via biosonar adjustments.
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Affiliation(s)
- Michael B Pedersen
- Marine Bioacoustics Lab, Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Kristian Beedholm
- Marine Bioacoustics Lab, Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Antoniya Hubancheva
- Acoustic and Functional Ecology, Max Planck Institute for Biological Intelligence, 82319 Seewiesen, Germany
- National Museum of Natural History, Bulgarian Academy of Sciences, 1000 Sofia, Bulgaria
| | - Kaloyana Koseva
- Marine Bioacoustics Lab, Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Astrid S Uebel
- Marine Bioacoustics Lab, Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Klaus Hochradel
- Private University for Health Sciences, Medical Informatics and Technology GmbH, 6060 Hall Tirol, Austria
| | - Peter T Madsen
- Marine Bioacoustics Lab, Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Laura Stidsholt
- Marine Bioacoustics Lab, Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
- Department of Evolutionary Ecology, Leibniz Institute for Zoo and Wildlife Research, 10315 Berlin, Germany
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Pedersen MB, Egenhardt M, Beedholm K, Skalshøi MR, Uebel AS, Hubancheva A, Koseva K, Moss CF, Luo J, Stidsholt L, Madsen PT. Superfast Lombard response in free-flying, echolocating bats. Curr Biol 2024; 34:2509-2516.e3. [PMID: 38744283 DOI: 10.1016/j.cub.2024.04.048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2024] [Revised: 03/20/2024] [Accepted: 04/22/2024] [Indexed: 05/16/2024]
Abstract
Acoustic cues are crucial to communication, navigation, and foraging in many animals, which hence face the problem of detecting and discriminating these cues in fluctuating noise levels from natural or anthropogenic sources. Such auditory dynamics are perhaps most extreme for echolocating bats that navigate and hunt prey on the wing in darkness by listening for weak echo returns from their powerful calls in complex, self-generated umwelts.1,2 Due to high absorption of ultrasound in air and fast flight speeds, bats operate with short prey detection ranges and dynamic sensory volumes,3 leading us to hypothesize that bats employ superfast vocal-motor adjustments to rapidly changing sensory scenes. To test this hypothesis, we investigated the onset and offset times and magnitude of the Lombard response in free-flying echolocating greater mouse-eared bats exposed to onsets of intense constant or duty-cycled masking noise during a landing task. We found that the bats invoked a bandwidth-dependent Lombard response of 0.1-0.2 dB per dB increase in noise, with very short delay and relapse times of 20 ms in response to onsets and termination of duty-cycled noise. In concert with the absence call time-locking to noise-free periods, these results show that free-flying bats exhibit a superfast, but hard-wired, vocal-motor response to increased noise levels. We posit that this reflex is mediated by simple closed-loop audio-motor feedback circuits that operate independently of wingbeat and respiration cycles to allow for rapid adjustments to the highly dynamic auditory scenes encountered by these small predators.
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Affiliation(s)
| | - Martin Egenhardt
- Section for Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Kristian Beedholm
- Section for Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | | | - Astrid Særmark Uebel
- Section for Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Antoniya Hubancheva
- Acoustic and Functional Ecology, Max Planck Institute for Biological Intelligence, 82319 Seewiesen, Germany; National Museum of Natural History, Bulgarian Academy of Sciences, 1000 Sofia, Bulgaria
| | - Kaloyana Koseva
- Section for Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Cynthia F Moss
- Department of Psychological and Brain Sciences, Departments of Neuroscience and Mechanical Engineering, Kavli Neuroscience Discovery Institute, Johns Hopkins University, Baltimore, MD 21218, USA
| | - Jinhong Luo
- Institute of Evolution and Ecology, School of Life Sciences, Central China Normal University, Wuhan 430079, China
| | - Laura Stidsholt
- Section for Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark; Department of Evolutionary Ecology, Leibniz Institute for Zoo and Wildlife Research, 10315 Berlin, Germany
| | - Peter Teglberg Madsen
- Section for Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
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Uebel AS, Pedersen MB, Beedholm K, Stidsholt L, Skalshøi MR, Foskolos I, Madsen PT. Daubenton's bats maintain stereotypical echolocation behaviour and a lombard response during target interception in light. BMC ZOOL 2024; 9:9. [PMID: 38679717 PMCID: PMC11057132 DOI: 10.1186/s40850-024-00200-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 04/21/2024] [Indexed: 05/01/2024] Open
Abstract
Most bats hunt insects on the wing at night using echolocation as their primary sensory modality, but nevertheless maintain complex eye anatomy and functional vision. This raises the question of how and when insectivorous bats use vision during their largely nocturnal lifestyle. Here, we test the hypothesis that the small insectivorous bat, Myotis daubentonii, relies less on echolocation, or dispenses with it entirely, as visual cues become available during challenging acoustic noise conditions. We trained five wild-caught bats to land on a spherical target in both silence and when exposed to broad-band noise to decrease echo detectability, while light conditions were manipulated in both spectrum and intensity. We show that during noise exposure, the bats were almost three times more likely to use multiple attempts to solve the task compared to in silent controls. Furthermore, the bats exhibited a Lombard response of 0.18 dB/dBnoise and decreased call intervals earlier in their flight during masking noise exposures compared to in silent controls. Importantly, however, these adjustments in movement and echolocation behaviour did not differ between light and dark control treatments showing that small insectivorous bats maintain the same echolocation behaviour when provided with visual cues under challenging conditions for echolocation. We therefore conclude that bat echolocation is a hard-wired sensory system with stereotyped compensation strategies to both target range and masking noise (i.e. Lombard response) irrespective of light conditions. In contrast, the adjustments of call intervals and movement strategies during noise exposure varied substantially between individuals indicating a degree of flexibility that likely requires higher order processing and perhaps vocal learning.
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Affiliation(s)
- Astrid Saermark Uebel
- Section for Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark.
| | | | - Kristian Beedholm
- Section for Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Laura Stidsholt
- Section for Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
- Department of Evolutionary Ecology, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany
| | | | - Ilias Foskolos
- Section for Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
- Section for Wildlife Ecology, Department of Ecoscience, Aarhus University, Aarhus, Denmark
| | - Peter Teglberg Madsen
- Section for Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
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Lewanzik D, Ratcliffe JM, Etzler EA, Goerlitz HR, Jakobsen L. Stealth echolocation in aerial hawking bats reflects a substrate gleaning ancestry. Curr Biol 2023; 33:5208-5214.e3. [PMID: 37898121 DOI: 10.1016/j.cub.2023.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 09/26/2023] [Accepted: 10/09/2023] [Indexed: 10/30/2023]
Abstract
Predator-prey co-evolution can escalate into an evolutionary arms race.1 Examples of insect countermeasures to bat echolocation are well-known,2 but presumptive direct counter strategies in bats to insect anti-bat tactics are rare. The emission of very low-intensity calls by the hawking Barbastella barbastellus to circumvent high-frequency moth hearing is the most convincing countermeasure known.2,3 However, we demonstrate that stealth echolocation did not evolve through a high-intensity aerial hawking ancestor becoming quiet as previously hypothesized2,3,4 but from a gleaning ancestor transitioning into an obligate aerial hawker. Our ancestral state reconstructions show that the Plecotini ancestor likely gleaned prey using low-intensity calls typical of gleaning bats and that this ability-and associated traits-was subsequently lost in the barbastelle lineage. Barbastelles did not, however, revert to the oral, high-intensity call emission that other hawking bats use but retained the low-intensity nasal emission of closely related gleaning plecotines despite an extremely limited echolocation range. We further show that barbastelles continue to emit low-intensity calls even under adverse noise conditions and do not broaden the echolocation beam during the terminal buzz, unlike other vespertilionids attacking airborne prey.5,6 Together, our results suggest that barbastelles' echolocation is subject to morphological constraints prohibiting higher call amplitudes and beam broadening in the terminal buzz. We suggest that an abundance of eared prey allowed the co-opting and maintenance of low-intensity, nasal echolocation in today's obligate hawking barbastelle and that this unique foraging behavior7 persists because barbastelles remain a rare, acoustically inconspicuous predator to eared moths. VIDEO ABSTRACT.
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Affiliation(s)
- Daniel Lewanzik
- Acoustic and Functional Ecology, Max Planck Institute for Biological Intelligence, Eberhard-Gwinner-Straße, 82319 Seewiesen, Germany; Department of Evolutionary Ecology, Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Str. 17, 10315 Berlin, Germany
| | - John M Ratcliffe
- Department of Biology, University of Toronto, 3359 Mississauga Road, Mississauga, ON L5L 1C6, Canada
| | - Erik A Etzler
- Department of Biology, University of Toronto, 3359 Mississauga Road, Mississauga, ON L5L 1C6, Canada
| | - Holger R Goerlitz
- Acoustic and Functional Ecology, Max Planck Institute for Biological Intelligence, Eberhard-Gwinner-Straße, 82319 Seewiesen, Germany
| | - Lasse Jakobsen
- Department of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark.
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5
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Kiai A, Clemens J, Kössl M, Poeppel D, Hechavarría J. Flexible control of vocal timing in Carollia perspicillata bats enables escape from acoustic interference. Commun Biol 2023; 6:1153. [PMID: 37957351 PMCID: PMC10643407 DOI: 10.1038/s42003-023-05507-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 10/25/2023] [Indexed: 11/15/2023] Open
Abstract
In natural environments, background noise can degrade the integrity of acoustic signals, posing a problem for animals that rely on their vocalizations for communication and navigation. A simple behavioral strategy to combat acoustic interference would be to restrict call emissions to periods of low-amplitude or no noise. Using audio playback and computational tools for the automated detection of over 2.5 million vocalizations from groups of freely vocalizing bats, we show that bats (Carollia perspicillata) can dynamically adapt the timing of their calls to avoid acoustic jamming in both predictably and unpredictably patterned noise. This study demonstrates that bats spontaneously seek out temporal windows of opportunity for vocalizing in acoustically crowded environments, providing a mechanism for efficient echolocation and communication in cluttered acoustic landscapes.
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Affiliation(s)
- Ava Kiai
- Institute for Cell Biology and Neuroscience, Goethe University, Frankfurt am Main, Germany.
| | - Jan Clemens
- European Neuroscience Center, Göttingen, Germany
| | - Manfred Kössl
- Institute for Cell Biology and Neuroscience, Goethe University, Frankfurt am Main, Germany
| | - David Poeppel
- Ernst Strüngmann Institute, Frankfurt am Main, Germany
| | - Julio Hechavarría
- Institute for Cell Biology and Neuroscience, Goethe University, Frankfurt am Main, Germany.
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Luo J, Lu M, Luo J, Moss CF. Echo feedback mediates noise-induced vocal modifications in flying bats. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2023; 209:203-214. [PMID: 36266485 DOI: 10.1007/s00359-022-01585-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Revised: 10/01/2022] [Accepted: 10/05/2022] [Indexed: 02/07/2023]
Abstract
Diverse animal taxa are capable of rapidly modifying vocalizations to mitigate interference from environmental noise. Echolocating bats, for example, must frequently perform sonar tasks in the presence of interfering sounds. Numerous studies have documented sound production flexibility in echolocating bats; however, it remains unknown whether noise-induced vocal modifications (NIVMs) mitigate interference effects on echoes or calls. In this study, we leverage echo level compensation behavior of echolocating bats to answer this question. Using a microphone array, we recorded echolocation calls of Hipposideros pratti trained to approach and land on a perch in the laboratory under quiet and noise conditions. We found that H. pratti exhibited echo level compensation behavior during approaching flights, which depended critically on distance to the landing perch. Broadcast noise delayed and affected the rate of echo level compensation in H. pratti. Moreover, H. pratti increased vocalization amplitude, i.e., exhibited the Lombard effect, while also adjusting call duration and bandwidth with increasing noise levels. Quantitative analyses of the data show that H. pratti relies on echo feedback, not vocal feedback, to adjust signals in the presence of noise. These findings provide compelling evidence that NIVMs in echolocating animals and non-echolocating animals operate through different mechanisms.
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Affiliation(s)
- Jinhong Luo
- Institute of Evolution and Ecology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China.
| | - Manman Lu
- Institute of Evolution and Ecology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Jie Luo
- Institute of Evolution and Ecology, School of Life Sciences, Central China Normal University, Wuhan, 430079, China
| | - Cynthia F Moss
- Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, MD, 21218, USA.
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Fernández Y, Dowdy NJ, Conner WE. High duty cycle moth sounds jam bat echolocation: bats counter with compensatory changes in buzz duration. J Exp Biol 2022; 225:jeb244187. [PMID: 36111562 PMCID: PMC9637272 DOI: 10.1242/jeb.244187] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 08/23/2022] [Indexed: 10/05/2023]
Abstract
Tiger moth species vary greatly in the number of clicks they produce and the resultant duty cycle. Signals with higher duty cycles are expected to more effectively interfere with bat sonar. However, little is known about the minimum duty cycle of tiger moth signals for sonar jamming. Is there a threshold that allows us to classify moths as acoustically aposematic versus sonar jammers based on their duty cycles? We performed playback experiments with three wild-caught adult male bats, Eptesicus fuscus. Bat attacks on tethered moths were challenged using acoustic signals of Bertholdia trigona with modified duty cycles ranging from 0 to 46%. We did not find evidence for a duty cycle threshold; rather, the ability to jam the bat's sonar was a continuous function of duty cycle consistent with a steady increase in the number of clicks arriving during a critical signal processing time window just prior to the arrival of an echo. The proportion of successful captures significantly decreased as the moth duty cycle increased. Our findings suggest that moths cannot be unambiguously classified as acoustically aposematic or sonar jammers based solely on duty cycle. Bats appear to compensate for sonar jamming by lengthening the duration of their terminal buzz and they are more successful in capturing moths when they do so. In contrast to previous findings for bats performing difficult spatial tasks, the number of sonar sound groups decreased in response to high duty cycles and did not affect capture success.
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Affiliation(s)
- Yohami Fernández
- Department of Biology, Wake Forest University, 1834 Wake Forest Road, Winston-Salem, NC 27109, USA
| | - Nicolas J. Dowdy
- Department of Biology, Wake Forest University, 1834 Wake Forest Road, Winston-Salem, NC 27109, USA
- Department of Zoology, Milwaukee Public Museum, 800 West Wells Street, Milwaukee, WI 53233, USA
| | - William E. Conner
- Department of Biology, Wake Forest University, 1834 Wake Forest Road, Winston-Salem, NC 27109, USA
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