DISCRIMINATION OF SINUSOIDALLY FREQUENCY-MODULATED SOUND SIGNALS MIMICKING SPECIES-SPECIFIC COMMUNICATION CALLS IN THE FM-BAT PHYLLOSTOMUS DISCOLOR

In the lesser spear-nosed bat, Phyllostomus discolor, maternal directi ve calls are characterized by an individual type of sinusoidal frequen cy modulation (= SFM) pattern. Beside modulation frequency, modulation depth, carrier frequency, and number of modulation cycles per call co ntribute to the mother's vocal signature. Since juvenile P. discolor l earn to adapt their isolation calls to the corresponding call characte ristics of the own mother or even to playback of a computer-stored dir ective call, if hand-reared in the absence of conspecifics, the bats' auditory system ought to be able to resolve interindividual difference s in communication call structure. However, quantitative psychoacousti c data on the discrimination of SFM signals in this species are not av ailable. Thus, in the present study, lesser spear-nosed bats were trai ned in a two-alternative forced-choice procedure to discriminate betwe en two alternatingly presented SFM sound signals differing in modulati on frequency. Other characteristics of acoustic stimuli were identical and designed to mimick the fundamental of species-specific calls. By gradually reducing the difference in modulation frequency between both stimuli within the behavioural relevant range until the animals' perf ormance dropped below the 75%-correct level, a considerable auditory s pectro-temporal resolution has been revealed. Particularly in comparis on to the overall interindividual variation of this call parameter (mi nimal modulation frequency = 49 Hz, maximum 100 Hz), the determined av erage difference limen for modulation frequency of 2.42 +/- 0.29 Hz se ems substantial and sufficient for labelling individuals.