An acoustically oriented article from the most recent issue (Volume
213, issue 19, 2010) of The Journal of Experimental Biology:
Koblitz JC, Stilz P, Schnitzler HU. J Exp Biol. 2010 213(19):3263-8.
Source levels of echolocation signals vary in correlation with wingbeat cycle in landing big brown bats (Eptesicus fuscus)
Abstract
Recordings
of the echolocation signals of landing big brown bats with a
two-dimensional 16-microphone array revealed that the source level
reduction of 7 dB per halving of distance is superimposed by a
variation of up to 12 dB within single call groups emitted during the
approach. This variation correlates with the wingbeat cycle. The timing
of call emission correlates with call group size. First pulses of
groups containing many calls are emitted earlier than first calls in
groups with fewer calls or single calls. This suggests that the
emission of pulse groups follows a fixed motor pattern where the
information gained from the preceding pulse group determines how many
calls will be emitted in the next group. Single calls and call groups
are centred at the middle of the upstroke. Expiration is indicated by
call emission. The pause between groups is centred at the middle of the
downstroke and indicates inspiration. The hypothesis that the source
level variation could be caused by changes in the subglottic pressure
due to the contraction of the major flight muscles is discussed.
Yossi Yovel
Department of Zoology,
Tel Aviv University, Israel
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