First published online April 17, 2009
Journal of Experimental Biology 212, 1392-1404 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.027045
Adaptive echolocation behavior in bats for the analysis of auditory scenes
Chen Chiu*,
Wei Xian and
Cynthia F. Moss
Department of Psychology, Neuroscience and Cognitive Science Program,
University of Maryland, College Park, MD 20742, USA
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Fig. 1. Illustration of assignment of echolocation calls to individual bats. The
sound speed is 346.65 m s–1; T1 and
T2 is the onset time of recorded calls at microphone 1 and
2, respectively; t1 and t2 is the
signal travel time from the bat to microphones 1 and 2, respectively, which
are estimated from video recordings; d1 and
d2 is the distance between bat and microphone 1 and 2,
respectively. Actual audio delay is calculated from audio recordings and is
equal to T1–T2. Estimated audio
delay is calculated from video recordings and is equal to
t1–t2. Values of real audio
delay and estimated audio delay are the same if one call was correctly
assigned to the vocalizing bat.
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Fig. 2. Two examples show the relative position of paired bats and the design of
their vocalizations. The 3-D flight paths of each bat in (A) example No. 1 and
(B) example No. 2. Arrows in the starting points of each flight curve marked
the flight direction of each bat. Flight trajectories of each bat were marked
by different colors (blue and red). One bat flew behind the other bat and
followed the leading bat's flight trajectory in example No. 1. Two bats flew
almost parallel in the beginning of example No. 2. The number beside each
flight path is the trial time and matched the x-axis in panel (B) and
(D), respectively. Each asterisk and open circle represents one vocalization
from bat A (asterisks) and bat B (open circles). The inter-bat distance and
call design of bat A and bat B are shown in (B) example No. 1 and (D) example
No. 2. The asterisks represent vocalizations from bat A and the open circles
represent vocalizations from bat B. From the upper to lower panels are
inter-bat distance, start/end frequencies (those two curves with higher values
are start frequencies and the other two are end frequencies), duration and
sweep rate.
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Fig. 3. Schematic representation of sequential call analysis. Each point represents
the start frequency of one vocalization, and different letters mean calls made
by different bats. For example, A1 is the first call bat A produced and B3 is
the third call bat B generated. The x-axis is the time and
y-axis is the start frequency of calls. Curves between two calls
represent two consecutive vocalizations produced by different bats and
absolute differences between these two sequential calls are used to represent
separation in paired bats' call design. Two consecutive calls, which were not
connected by curves, were not included in data analysis because they were
produced by the same individual.
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Fig. 4. Distribution of call design separation between two sequential calls
produced by different bats when they flew together. The thick black line in
each histogram indicates the baseline separation, which is the difference in
call design between two bats when they each flew alone. The percentages mark
the proportion of calls that exceed the baseline separation. Call parameters
analyzed here are (A) start frequency, (B) end frequency, (C) bandwidth, (D)
duration and (E) sweep rate.
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Fig. 5. The correlation between each pair's baseline separation and the magnitude
of adjustment from baseline to two-bat condition in (A) start frequency, (B)
end frequency, (C) bandwidth, (D) duration and (E) sweep rate.
*Means P<0.05 and ** means
P<0.01. Each data point represents one bat pair and the number
next to each point refers to different bat pairs. Only spectral parameters,
start/end frequencies and bandwidth, show significant negative
correlation.
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Fig. 6. The correlation between start/end frequencies separation and proportion of
calls with higher start/end frequencies than the preceding call. The closed
circles represent start frequency and the open circles represent end frequency
in each bat pair. The bat with higher start frequency tended to keep a higher
frequency than the other bat in the pair when the start frequency separation
is large for this pair. End frequency shows a similar trend to start
frequency.
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Fig. 7. The mean comparison of each call design separation between two consecutive
calls at different inter-bat distance by one-way analysis of variance (ANOVA).
Error bars indicate standard error of mean. Different letters mean that there
is a significant difference between these two values. The dotted line in each
panel shows the baseline separation. Call designs are measured by five
parameters: (A) start frequency, (B) end frequency, (C) bandwidth, (D)
duration and (E) sweep rate.
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Fig. 8. The amount of deviation from baseline data in the two-bat condition for
each bat in each pair. White and gray bars indicate data from different bats
in a pair. Five call parameters were presented here: (A) start frequency, (B)
end frequency, (C) bandwidth, (D) duration and (E) sweep rate. All deviated
amounts are either significantly larger or smaller than zero, except those
marked with n.s. The x-axis shows bat pairs and these bat pair
numbers correspond to those shown in Fig.
5. Error bars represent standard error of the mean.
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Fig. 9. The magnitude of call design adjustment from baseline to two-bat condition
as a function of pulse intervals. Error bats indicate standard error of mean
and different letters mean that there is a significant difference between
these two values. The x-axis is the pulse interval of individual bats
and the y-axis is the magnitude of adjustment for five call
parameters: (A) start frequency, (B) end frequency, (C) bandwidth, (D)
duration and (E) sweep rate.
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© The Company of Biologists Ltd 2009
