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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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Foskolos I, Pedersen MB, Beedholm K, Uebel AS, Macaulay J, Stidsholt L, Brinkløv S, Madsen PT. Echolocating Daubenton's bats are resilient to broadband, ultrasonic masking noise during active target approaches. J Exp Biol 2022; 225:274313. [DOI: 10.1242/jeb.242957] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Accepted: 12/20/2021] [Indexed: 11/20/2022]
Abstract
Echolocating bats hunt prey on the wing under conditions of poor lighting by emission of loud calls and subsequent auditory processing of weak returning echoes. To do so, they need adequate echo-to-noise ratios (ENRs) to detect and distinguish target echoes from masking noise. Early obstacle avoidance experiments report high resilience to masking in free-flying bats, but whether this is due to spectral or spatiotemporal release from masking, advanced auditory signal detection or an increase in call amplitude (Lombard effect) remains unresolved. We hypothesized that bats with no spectral, spatial or temporal release from masking noise, defend a certain ENR via a Lombard effect. We trained four bats (Myotis daubentonii) to approach and land on a target that broadcasted broadband noise at four different levels. An array of seven microphones enabled acoustic localization of the bats and source level estimation of their approach calls. Call duration and peak frequency did not change, but average call source levels (SLRMS, at 0.1 m as dB re. 20 µPa, root-mean-square) increased, from 112 dB in the no-noise treatment, to 118 dB (maximum 129 dB) at the maximum noise level of 94 dB. The magnitude of the Lombard effect was small (0.13 dB SLRMS/dB of noise), resulting in mean broadband and narrowband ENRs of -11 and 8 dB respectively at the highest noise level. Despite these poor ENRs, the bats still performed echo-guided landings, making us conclude that they are very resilient to masking even when they cannot avoid it spectrally, spatially or temporally.
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Affiliation(s)
- Ilias Foskolos
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | | | - Kristian Beedholm
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | | | - Jamie Macaulay
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Laura Stidsholt
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
| | - Signe Brinkløv
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
- Department of Ecoscience - Wildlife Ecology, Aarhus University, 8410 Rønde, Denmark
| | - Peter Teglberg Madsen
- Zoophysiology, Department of Biology, Aarhus University, 8000 Aarhus, Denmark
- Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus, Denmark
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