Stetharasa exarmata

(1 male recorded) This species was abundant at night in Ueumari on low understory vegetation beside the trails in undisturbed forest. But only one male's calls were recorded this back in Canada and inadvertently, in the background of a recording of Typophyllum (see below). For this reason microphone allignment and distance are not known. This male produced several songs, each lasting a bit less than 2 s. Mean duration of songs (n = 4) was 1.8 s. In each call he produced 6 phonatomes in succession (Fig. 39A). The first minor train of this sequence was distinctive, comprised of >40 pulses, peak pulse amplitudes incrementing linearly throughout the train to a maximum typical of later minor trains (Fig. 39A). The male was apparently inhibited from singing until the completion of calling bouts of the Typophyllum. On another occasion he produced only 3 phonatomes, taking 0.9 s, perhaps due to interference from the Typophyllum. The song can be described as a short rattle, faint to all but young ears.

In the call proper all pulses are rapid-decay, each phonatome (Fig. 39B) a minor (lower amplitude) train combining with a more intense major train. The resulting low-Q spectrum contains a coherent band of carrier frequencies between 16 and 34 kHz (Fig. 39 C,D). The energy is distributed rather uniformly over this band so there is no identifiable peak frequency. And there is no appreciable difference between the spectra of the two train types (putative opening and closing movements) (compare Fig. 39 C,D).

The phonatome period of S. exarmata is 272 ms. The phonatome rate at about 20 °C was 3.2/s. There are 42 pulses in the minor train delivered at a rate of 420/s, while there are 32 pulses in the major train occurring at a rate of 220/s.
Notable in this species is the unusual coherence and temporal separation of the pulses of the minor pulse train and its rather long duration, about 100 ms. The teeth of the file, upon a low buttress, are remarkably uniform in width and spacing (Fig. 25 A,B). Perhaps this file morphology relates to the clearer separation of pulses in time. The train duration is very long in comparison to other non-resonance singers (e.g- Conocephalus spp.). [1]

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