Investigation of echolocation pulse in Pipistrellus abramus during paired flight using discriminant analysis
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1
Doshisha University, Faculty of Life and Medical Sciences, Japan
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2
Doshisha University, Faculty of Engineering, Japan
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3
Doshisha University, Faculty of Life and Medical Sciences, Neurosensing and Bionavigation Research Center, Japan
Echolocating bats are often observed to forage in the field with many conspecifics. Although the jamming sounds from neighboring bats may cause acoustic interference, bats appear to have a capability to discriminate their own retuning echoes from other neighboring bats sounds. In this study, we investigated the echolocation sounds of FM echolocating bat (Pipistrellus abramus) flying in pairs (paired flight) using onboard telemetry microphones (Telemike) in a flight chamber. P. abramus emits broadband FM pulses with harmonics and a fundamental component downwardly modulated from 100 to 40 kHz. Emitted pulses were recorded individually by each of the Telemikes that were mounted on the backs of two bats. We analyzed the recorded pulses using a linear discriminant analysis (DA), so that we could quantitatively compare the acoustical characteristics of the emitted pulses between single and paired flights. The DA was conducted for five explanatory variables of call parameters: terminal frequency of pulse (TF), bandwidth (BW), peak frequency (Peak-F), duration and sweep rate (BW / duration). Bats generally change these call parameters with a target distance, therefore we used only the pulses emitted by the bats when the bats were flying at the restricted area during free flight in the flight chamber. Data were taken from a total of 22 flights of 12 pairs among 11 individuals.
The means of percentages of echolocation pulses that were correctly classified between two bats were 95% during single and paired flights. Besides in 43% of the total flights (single flight; 9/22, paired flight; 10/22), pulses emitted by two bats were perfectly classified. This suggests that inherent individual difference in these call parameters among individuals were statistically discriminated in P. abramus. Moreover, the DA showed that the TF was found to be the most important factor among the five call parameters for discrimination of bat’s pulse both in single and paired flight.
The means of TFs among 11 individuals ranged from approximately 40 kHz to 47 kHz. The means of difference in the TFs between two bats (⊿TF) during single and paired flights were small; 2.3±1.4 kHz and 1.8±1.1 kHz, respectively. In 18 flights, the TFs were different between single and paired flights, but 61% of these flights (11/18) decreased the ⊿TF during paired flight.
To investigate how the difference in TF affects the discrimination of FM sounds in the context of ambiguity of own and other sounds during echolocating, we calculated cross-correlation functions of two artificial FM sounds when the TF of one sound was shifted (ambiguity function). Accordingly, small TF shift (<2 kHz) adequately weakened the cross-correlation between two FM sounds, suggesting that shifting frequency range by 1-2 kHz (bandwidth; 60 kHz) appeared to be effective to discriminate individual FM sounds in p. abramus. Our findings suggest that small difference in TF may be one of attributed factors of echolocation pulses emitted by bats flying in pair to discriminate their own pulses from conspecifics with suitable interindividual disparities of call parameter.
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:
Ambiguity function,
Jamming avoidance,
Telemike,
Terminal frequency
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Orientation and Navigation
Citation:
Takahashi
E,
Kagami
Y,
Watanabe
Y,
Riquimaroux
H,
Ohta
T and
Hiryu
S
(2012). Investigation of echolocation pulse in Pipistrellus abramus during paired flight using discriminant analysis.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00228
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Received:
30 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Shizuko Hiryu, Doshisha University, Faculty of Life and Medical Sciences, Neurosensing and Bionavigation Research Center, Kyoto Prefecture, 610-0394, Japan, shiryu@mail.doshisha.ac.jp