, Volume 139, Issue 4, pp 349-356

Hearing characteristics and doppler shift compensation in South Indian CF-FM bats

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  1. Echolocation pulses, Doppler shift compensation behaviour under laboratory conditions and frequency response characteristics of hearing were recorded inRhinolophus rouxi, Hipposideros speoris andHipposideros bicolor.

  2. The frequencies of the constant frequency portions of the CF-FM pulses lie at about 82.8 kHz forR. rouxi from Mahabaleshwar, at 85.2 kHz forR. rouxi from Mysore. Hipposiderid bats have considerably higher frequencies at 135 kHz inH. speoris and 154.5 kHz inH. bicolor. The mean sound durations were 50 ms, 6.4 ms and 4.7 ms, respectively.

  3. R. rouxi compensates for Doppler shifts in a range up to typically 4 kHz of positive Doppler shifts (Fig. 2). The Doppler shift compensation behaviour is almost identical to that ofR. ferrumequinum.

  4. H. speoris andH. bicolor do not compensate for Doppler shifts under laboratory conditions. Doppler shifts in the echoes induce emission frequency changes which are not correlated to the presented Doppler shifts (Fig. 3).

  5. The frequency response characteristics of hearing ofR. rouxi show characteristic sensitivity changes near the bat's reference frequency as also found inR. ferrumequinum. The threshold differences between the low threshold at the reference frequency and a few hundred Hz below are 40 to 50 dB in awake bats (Fig. 5).

  6. Frequency sensitivity changes near the emitted CF-frequency of the bats are less pronounced inH. speoris or almost absent inH. bicolor.

Supported by grants from Deutsche Forschungsgemeinschaft DFG Ne 146/9, Schu 390/1,2; the University Grants Commission of India, code No 430 and the Deutscher Akademischer Austauschdienst
I wish to thank Prof. Krishnaswami and Dr. Chandrashekaran for their kind support of this work during my stay at the School of Biological Sciences, University of Madurai (India). The support of the University Grants Commission of the Government of India is gratefully acknowledged. The technical assistance of Ms. H. Hahn and Ms. A. Polotzek was most helpful.