QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online May 1, 2006
Journal of Experimental Biology 209, 1816-1826 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02194

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JEB Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Holderied, M. W. Articles by von Helversen, O. Search for Related Content PubMed PubMed Citation Articles by Holderied, M. W. Articles by von Helversen, O.

Flight and echolocation behaviour of whiskered bats commuting along a hedgerow: range-dependent sonar signal design, Doppler tolerance and evidence for `acoustic focussing'

Marc W. Holderied^1,2,*, Gareth Jones¹ and Otto von Helversen²

¹ School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
² Department of Zoology II, University of Erlangen, Staudtstr. 5, 91058 Erlangen, Germany

View larger version (34K): [in a new window]   Fig. 1. Three examples of the effect of call design on ranging errors. (A–C) Spectrograms (FFT size 512, 256 points Hanning window, 240 points overlap). Two calls (A,C) were emitted at the locations indicated in Fig. 7B by stars. DOF indicates the distance at which overall ranging errors were zero. (D–F) Ranging errors calculated for these calls and indicated as lines of identical error. Labels on lines indicate size of ranging error in centimetres (>0 represents overestimation and <0 represents underestimation of distance). The thick line labelled `focus' indicates locations where the overall ranging error is zero. (G–I) Ranging errors as in D–F but for a smaller distance range. `Pinheads' indicate perceived positions and `pin tips' the actual positions of targets.

View larger version (30K): [in a new window]   Fig. 2. Four examples of the influence of call bandwidth and frequency modulation curvature on Doppler-related ranging errors at a flight speed of 8 m s–1. Upper row: spectrograms of four call echo pairs. Lower row: envelope of the cross correlation function (CCF). Arrows indicate the actual time delay of 8 ms between call and echo. Red lines show the position of the peak in the CCF.

View larger version (41K): [in a new window]   Fig. 3. Flight behaviour along the hedge. (A) 3-D surface of the hedge; (B) as in A, but with all flight paths; (C–F) flight corridor in four cross sections through the hedge and flight paths at the Y-positions indicated; (G) individual instantaneous distance to the hedge; (H) individual flight speed during the flight along the hedge. Flight direction from right to left, i.e. with decreasing Y.

View larger version (12K): [in a new window]   Fig. 4. Echolocation behaviour along the hedge (means ± s.d.) in segments of 1 m. (A) pulse interval; (B) pulse duration; (C) bandwidth of the first harmonic; (D) Doppler ranging error; (E) width of the cross correlation function (CCF) envelope, i.e. inverse measure of Doppler ranging acuity, for a flight speed of 6 m s–1.

View larger version (41K): [in a new window]   Fig. 5. Signal overlap zone (SOZ) of nine individual bats flying along the hedge. Flight direction from right to left. The first individual in the upper row was the only one not using the corridor below the hedge. Hemispheres indicate the sizes of the SOZ plotted around the position of the bat at the time of each call.

View larger version (40K): [in a new window]   Fig. 6. Distance of focus (DOF) of the same nine individual bats flying along the hedge as in Fig. 5. Flight direction from right to left. The first individual in the upper row was the only one not using the corridor below the hedge. Hemispheres indicate the surface of zero ranging error, i.e. a hemisphere with the DOF as its radius, plotted around the position of the bat at the time of each call.

View larger version (22K): [in a new window]   Fig. 7. Distance of focus (DOF) and signal overlap zone (SOZ) in relation to position to the hedge (shaded area). (A) Three-dimensional representation of the flight paths of 22 bats and of the hedge they were flying along. The open rectangle at Y=2 m indicates the size and position of the cross section shown in B and C. (B) Cross section through the hedge and flight paths as indicated by the rectangle in A. Symbols show where each individual bat has passed the cross-sectional plane. Circles around symbols have a radius that equals the DOF of the call emitted by the particular bat closest to the cross sectional plane. (C) Same cross-section as in B, with circles indicating the limit of SOZ.