Beam-width control of echolocation pulses in Japanese CF-FM bats (Rhinolophus ferrumequinum nippon) during aerial prey hunting.
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1
Doshisha University, Faculty of Life and Medical Sciences, Neurosensing and Bionavigation Research Center, Japan
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2
Doshisha University, Faculty of Engineering, Japan
Echolocating bats emit ultrasounds and analyze returning echoes in order to search and capture a prey. When the bats approach a target prey, they increase the pulse repetition rate and shorten the pulse duration, which are considered to be common features of echolocation behaviors in both CF-FM and FM bat species. Beam width of emitted pulse and its direction also provide us important indexes about spatial window where bats can receive echoes from surrounding objects, and about their attention. In this study, we examined the echolocation sounds of Japanese CF-FM bats (Rhinolophus ferrumequinum nippon) while they pursued a fluttering moth (Goniocraspidum pryeri) using 31-ch microphone array system. The measurement was combined with telemetry microphone (Telemike) recording, that was mounted on the bats during the flight. Horizontal and vertical arrays (17 ch: horizontal plane, 17 ch: vertical plane, 3 ch: both planes) were arranged to measure 3-D beam direction and width of the pulses emitted by bats during moth-capture flight in a flight chamber. By monitoring both of the flight trajectories of bats and moths using high-speed video cameras, we investigated how CF-FM bats adjust the pulse direction and beam width (-6dB angles) according to the position of the prey.
When the bat was flown by the experimenter from one end of the flight chamber, the bat directly approached toward the moth and then attacked (grasped in the wing) the tethered fluttering moth. During search and approach phases, the means of horizontal and vertical beam widths (21 flight sessions of 7 bats) were 22 ± 5˚ (mean ± S.D., n = 297) and 13 ± 5˚ (n = 276), respectively. When the bat started the terminal phase at approximately 1 m from the moth, G. pryeri sometime showed distinctive evasive flight (54%, 50 of 93 fights) responding to bat’s approach, i.e., suddenly change its flight direction with increase in its flight velocity. At the same time, the beam width of some emissions was significantly broadened in both horizontal (44 %, 249 of 565 pulses) and vertical planes (n = 401, 71 % of 565 pulses). The mean of the broadened beam width was 36 ± 7˚ (horizontal) and 30 ± 9˚ (vertical), respectively.
In 98 % of all emitted pulses during search and approach phases, the beam width of the pulse was wider than the misalignment (target direction – pulse direction). We could think when the moth starts its evasive flight, tracking accuracy of bat’s echolocation would decrease compared to that during the approach phase. However, we found that the misalignment of 97% of emissions during the terminal phase was smaller than their broadened beam width. These findings indicate that the bats actively adjusted their beam width to retain moving target in spatial window of echolocation at final stage of capturing.
Acknowledgements
[Research supported by a Grant-in-Aid for Scientific Research on Innovative Areas (Grant No. 20200055), a Grant-in-Aid for Young Scientists (B) (Grant No. 21760318) of JSPS, and an Office of Naval Research (ONR) grant].
Keywords:
Biosonar,
telemetry microphone
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Orientation and Navigation
Citation:
Hiryu
S,
Matsuta
N,
Riquimaroux
H and
Watanabe
Y
(2012). Beam-width control of echolocation pulses in Japanese CF-FM bats (Rhinolophus ferrumequinum nippon) during aerial prey hunting..
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00171
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Received:
27 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Shizuko Hiryu, Doshisha University, Faculty of Life and Medical Sciences, Neurosensing and Bionavigation Research Center, Kyotanabe, Kyoto, 610-0321, Japan, shiryu@mail.doshisha.ac.jp