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First published online December 16, 2008
Journal of Experimental Biology 212, 11-20 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.023226
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Intense echolocation calls from two `whispering' bats, Artibeus jamaicensis and Macrophyllum macrophyllum (Phyllostomidae)

Signe Brinkløv1,*, Elisabeth K. V. Kalko2,3 and Annemarie Surlykke1

1 Institute of Biology, University of Southern Denmark SDU, Campusvej 55, 5230 Odense M, Denmark
2 Institute of Experimental Ecology, University of Ulm, Albert-Einstein Allee 11, D-89069 Ulm, Germany
3 Smithsonian Tropical Research Institute, P.O. Box 0843-03092 Balboa, Ancon, Republic of Panamá


Figure 1
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  		Fig. 1. (A) The flight room setup used to record M. macrophyllum while the bats flew over a pool, approaching and gaffing mealworms from the surface. Echolocation sounds were recorded with an array with four microphones (M1–M4) and flight behaviour documented by an infrared (IR) video camera. (B) A four-channel recording with Time-Of-Arrival-Differences (TOADs, thick broken red lines) due to the distance between the microphones. TOADs were determined by cross-correlating the four channel recordings of a signal using the one with highest amplitude (green) as the model. Thin broken red lines mark the start and end of signals on each channel.

 

Figure 2
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  		Fig. 2. Spectrograms and power spectra from M. macrophyllumind (A) and A. jamaicensis (B). The spectrograms (FFT size 512, Hanning window, complete duration 1000 ms) show echolocation sequences recorded from bats approaching food on the wing. For each of the two species selected signals are shown below in expanded spectrograms (total duration 5 ms) and as power spectra (FFT size 1024). M. macrophyllum has distinct search, approach and terminal buzz phases where repetition rate increases from 42 calls s–1 to 132 calls s–1 whereas pulse duration decreases from 1.7 ms (A left black box) to 0.8 ms (A right black box). A. jamaicensis calls change from single emissions to grouping of calls with repetition rates up to 20 calls s–1. Pulse duration is 1.7 ms (B left black box) and 1.2 ms (B right black box). Bandwidth does not change considerably for either species.

 

Figure 3
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  		Fig. 3. Four-channel recordings of search signals and corresponding 3-D flight paths for M. macrophyllumind and A. jamaicensis. The configuration of the array is shown as closed circles connected with blue lines in the correct position relative to the flight paths as well as enlarged between the two graphs.

 

Figure 4
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  		Fig. 4. Scatter plots of source levels from M. macrophyllumind, M. macrophyllumgroup and A. jamaicensis as a function of distance to the array. For M. macrophyllumind and A. jamaicensis, mean source levels increased the further away the bats were from the array up to 2 m. Beyond 2 m, source levels were independent of distance and mean values are indicated by the horizontal trend lines. There was no correlation between distance and source level for M. macrophyllumgroup.

 

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© The Company of Biologists Ltd 2009