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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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Related in: MedlinePlus

(a) The set-up with a linear horizontal array of three microphones and one microphone above the middle microphone. The microphones were separated by 1 m. The array was set with the horizontal microphones 30 cm over the water of a pond, where M. daubentonii hunted every night. The four microphones are marked with green numbers on the array and on the corresponding channels of the recording. We determined the (b) time-of-arrival differences (TOAD) of the sonar sounds between recording channels by cross-correlation.
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fig1: (a) The set-up with a linear horizontal array of three microphones and one microphone above the middle microphone. The microphones were separated by 1 m. The array was set with the horizontal microphones 30 cm over the water of a pond, where M. daubentonii hunted every night. The four microphones are marked with green numbers on the array and on the corresponding channels of the recording. We determined the (b) time-of-arrival differences (TOAD) of the sonar sounds between recording channels by cross-correlation.

Mentions: In 2003, we used a linear array with three microphones, 1 m apart. In 2005, we added an extra microphone 1 m above the middle microphone in the array (figure 1). The three aligned microphones were 30 cm above the water at approximately 0.5 m horizontal distance from the brink. The microphones (1/4″ BF GRAS microphones without grids) were mounted on thin (5 mm) rods. Signals were amplified (GRAS 12AA, with custom-built 13 kHz high-pass (HP) filter) and recorded digitally (sampling rate 250 kHz per channel, eight order low-pass anti-aliasing filter with f−3 dB=110 kHz) using three or four channels on a Wavebook 512 (IOtech, Cleveland, OH, USA) A/D and stored on an IBM notebook computer, which was also used to check the recordings online. The Wavebook had 128 MB circulating buffer memory, allowing for manual post-triggering with delay set to 3 s. We only recorded bats approaching the array at an angle of approximately 30°.


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

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

(a) The set-up with a linear horizontal array of three microphones and one microphone above the middle microphone. The microphones were separated by 1 m. The array was set with the horizontal microphones 30 cm over the water of a pond, where M. daubentonii hunted every night. The four microphones are marked with green numbers on the array and on the corresponding channels of the recording. We determined the (b) time-of-arrival differences (TOAD) of the sonar sounds between recording channels by cross-correlation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig1: (a) The set-up with a linear horizontal array of three microphones and one microphone above the middle microphone. The microphones were separated by 1 m. The array was set with the horizontal microphones 30 cm over the water of a pond, where M. daubentonii hunted every night. The four microphones are marked with green numbers on the array and on the corresponding channels of the recording. We determined the (b) time-of-arrival differences (TOAD) of the sonar sounds between recording channels by cross-correlation.
Mentions: In 2003, we used a linear array with three microphones, 1 m apart. In 2005, we added an extra microphone 1 m above the middle microphone in the array (figure 1). The three aligned microphones were 30 cm above the water at approximately 0.5 m horizontal distance from the brink. The microphones (1/4″ BF GRAS microphones without grids) were mounted on thin (5 mm) rods. Signals were amplified (GRAS 12AA, with custom-built 13 kHz high-pass (HP) filter) and recorded digitally (sampling rate 250 kHz per channel, eight order low-pass anti-aliasing filter with f−3 dB=110 kHz) using three or four channels on a Wavebook 512 (IOtech, Cleveland, OH, USA) A/D and stored on an IBM notebook computer, which was also used to check the recordings online. The Wavebook had 128 MB circulating buffer memory, allowing for manual post-triggering with delay set to 3 s. We only recorded bats approaching the array at an angle of approximately 30°.

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