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Echolocating bats emit a highly directional sonar sound beam in the field.

Surlykke A, Boel Pedersen S, Jakobsen L - Proc. Biol. Sci. (2009)

Bottom Line: At 55kHz half-amplitude angle was 40 degrees in the laboratory versus 20 degrees in the field.The relationship between frequency and directionality can be explained by the simple piston model.The model also suggests that the increase in the emitted intensity in the field is caused by the increased directionality, focusing sound energy in the forward direction.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biology, University of Southern Denmark, 5230 Odense M, Denmark. ams@biology.sdu.dk

ABSTRACT
Bats use echolocation or biosonar to navigate and find prey at night. They emit short ultrasonic calls and listen for reflected echoes. The beam width of the calls is central to the function of the sonar, but directionality of echolocation calls has never been measured from bats flying in the wild. We used a microphone array to record sounds and determine horizontal directionality for echolocation calls of the trawling Daubenton's bat, Myotis daubentonii, flying over a pond in its natural habitat. Myotis daubentonii emitted highly directional calls in the field. Directionality increased with frequency. At 40kHz half-amplitude angle was 25 degrees , decreasing to 14 degrees at 75kHz. In the laboratory, M. daubentonii emitted less intense and less directional calls. At 55kHz half-amplitude angle was 40 degrees in the laboratory versus 20 degrees in the field. The relationship between frequency and directionality can be explained by the simple piston model. The model also suggests that the increase in the emitted intensity in the field is caused by the increased directionality, focusing sound energy in the forward direction. The bat may increase directionality by opening the mouth wider to emit a louder, narrower beam in the wild.

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(a,b) Isolation of first harmonic. The echolocation calls were broadband FM sweeps with a prominent second harmonic. The first harmonic was isolated by harmonic filtering, which removed the interference in time signals and spectra that was due to the frequency overlap between first and second harmonic.
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fig2: (a,b) Isolation of first harmonic. The echolocation calls were broadband FM sweeps with a prominent second harmonic. The first harmonic was isolated by harmonic filtering, which removed the interference in time signals and spectra that was due to the frequency overlap between first and second harmonic.

Mentions: We compensated for transmission loss due to the distance to the bat, i.e. spherical spreading loss (−6 dB per doubling of distance) and frequency-dependent atmospheric attenuation at 16°C and 80 per cent relative humidity (ANSI 1978) corresponding to the average climatic conditions at the study site. We also compensated for the directionality of the 1/4″ microphones (Brüel & Kjær 1982). To determine the directionality of the first harmonic, we had to isolate it, but simple low-pass filtering was inadequate due to the frequency overlap between the first and second harmonic. A program employing a graphic method developed by Beedholm (2004) was used for harmonic filtering (figure 2). All SPLs are given as dB SPL relative to 20 μPa rms (root mean square).


Echolocating bats emit a highly directional sonar sound beam in the field.

Surlykke A, Boel Pedersen S, Jakobsen L - Proc. Biol. Sci. (2009)

(a,b) Isolation of first harmonic. The echolocation calls were broadband FM sweeps with a prominent second harmonic. The first harmonic was isolated by harmonic filtering, which removed the interference in time signals and spectra that was due to the frequency overlap between first and second harmonic.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2664374&req=5

fig2: (a,b) Isolation of first harmonic. The echolocation calls were broadband FM sweeps with a prominent second harmonic. The first harmonic was isolated by harmonic filtering, which removed the interference in time signals and spectra that was due to the frequency overlap between first and second harmonic.
Mentions: We compensated for transmission loss due to the distance to the bat, i.e. spherical spreading loss (−6 dB per doubling of distance) and frequency-dependent atmospheric attenuation at 16°C and 80 per cent relative humidity (ANSI 1978) corresponding to the average climatic conditions at the study site. We also compensated for the directionality of the 1/4″ microphones (Brüel & Kjær 1982). To determine the directionality of the first harmonic, we had to isolate it, but simple low-pass filtering was inadequate due to the frequency overlap between the first and second harmonic. A program employing a graphic method developed by Beedholm (2004) was used for harmonic filtering (figure 2). All SPLs are given as dB SPL relative to 20 μPa rms (root mean square).

Bottom Line: At 55kHz half-amplitude angle was 40 degrees in the laboratory versus 20 degrees in the field.The relationship between frequency and directionality can be explained by the simple piston model.The model also suggests that the increase in the emitted intensity in the field is caused by the increased directionality, focusing sound energy in the forward direction.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biology, University of Southern Denmark, 5230 Odense M, Denmark. ams@biology.sdu.dk

ABSTRACT
Bats use echolocation or biosonar to navigate and find prey at night. They emit short ultrasonic calls and listen for reflected echoes. The beam width of the calls is central to the function of the sonar, but directionality of echolocation calls has never been measured from bats flying in the wild. We used a microphone array to record sounds and determine horizontal directionality for echolocation calls of the trawling Daubenton's bat, Myotis daubentonii, flying over a pond in its natural habitat. Myotis daubentonii emitted highly directional calls in the field. Directionality increased with frequency. At 40kHz half-amplitude angle was 25 degrees , decreasing to 14 degrees at 75kHz. In the laboratory, M. daubentonii emitted less intense and less directional calls. At 55kHz half-amplitude angle was 40 degrees in the laboratory versus 20 degrees in the field. The relationship between frequency and directionality can be explained by the simple piston model. The model also suggests that the increase in the emitted intensity in the field is caused by the increased directionality, focusing sound energy in the forward direction. The bat may increase directionality by opening the mouth wider to emit a louder, narrower beam in the wild.

Show MeSH
Related in: MedlinePlus