, Volume 136, Issue 3, pp 227-233

Behavioral audiogram and masked thresholds of the megachiropteran echolocating bat,Rousettus

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  1. A behavioral auditory threshold obtained by operant conditioning of the megachiropteran bat,Rousettus aegyptiacus, is described.

  2. The auditory threshold in quiet has a maximum sensitivity between 8 and 10 kHz, separated by an 8 to 10 dB rise from a second more sharply tuned peak at 20 kHz (Fig. 2). The minimum mean threshold is 44 dB SPL at 10 kHz. No response was obtained to sounds below 1 kHz or above 30 kHz.

  3. The amount of masking produced by the presence of broad band noise with a spectrum level of 31.7 dB SPL varies between a minimum at 2 kHz of 10.1 dB and a maximum at 20 kHz of 21.9 dB (Fig. 2).

  4. The critical ratio is smallest (29 dB) at 8 kHz. It increases gradually at higher frequencies in a manner similar to other mammals studied, but is unusual in rising very steeply at lower frequencies (Fig. 3).

  5. The masked threshold at 12 kHz increases only about 11 dB when the stimulus duration is decreased from 250 ms to 2 ms (Fig. 4).

  6. The acoustic orientation ofRousettus is discussed in relation to these psychophysical data.

We are especially grateful to Drs. D.E. Robinson and G.R. Long for advice during the course of these experiments and for their critical comments on this manuscript. Ms. Michele Wright provided valuable assistance during some of the experiments and in preparation of the manuscript. This research was supported by grant GB 42755 from N.S.F. to R.A.S.