Macrochiton macromelos

(2 males recorded) Full-range recordings were made of a caged singer (86-1) at 15cm distance, at dorsal and ventral aspectes (18-19°C). From this male we obtained 5 calls. One song of a second male (86-2). caged separately, was recorded in the background. The two insects influenced the incidence of each other's calling. For both males acoustic output was interspersed several times with bouts of calling tremulations (see below):

Pooled average song period (n=3) for 86-1 was 3.4s. Average duration of the songs of 86-1 was 1079 ms; the single recorded song of 86-2 lasted 1110 ms. Fig. 41 A shows two successive songs of 86-1.
In real time a human listener hears a short trill, musical with detectable infrastructure. The latter is due to a train of sinusoidal pulses which comprises each song (Fig. 41B). Each phona tome in this species apparently corresponds to a single sinusoidal pulse (Fig. 41C). On average a train contained 19.5 prolonged pulses (range 13-25). given at a quite uniform pulse rate. Mean number of pulses per call was 18.8 for 86-1; male 86-2 in his single song had 23 pulses. Pulse peak amplitude increased during the call to a maximum about 2/3 of the way through, then declined somewhat.

Pulse amplitude envelopes were very variable (Fig. 41C). rising very gradually from onset to become a plateau (Fig41D) and then sometimes taking on the appearance of beats (Fig. 41E). Mean pulse duration was 26.9 ms and mean pulse period was 53.9 ms, calculated on the basis of all pulses in all available calls for both males. The waveform is highly sinusoidal (Fig. 41D).

The power spectrum is high-Q, dominated by a single narrow peak in the middle audio range (Fig. 41 H). For 86-1 the average carrier was 13.6 kHz (c.v.5.1%) and the width of the peak 18 dB down was 3 kHz (12.5-15.4 kHz). The other
male had a carrier of 14.0 kHz. The occurrence of beats (compare Fig. 41 D and E, taken from the pulse regions indicated by the arrows) suggests the existence on the generator of two non-harmonically related frequency sources (12.5 and 14.5 kHz). These are not always active at the same time, so that as in Fig. 41. D, E, a level-amplitude wave corresponds to a single very high-Q peak at 12.5 kHz. When the waveform is amplitude modulated as a series of beats (Fig. 41E) one sees two peaks 12.9 and 14.5 kHz (Fig. 41G).

Both recorded males of this species were also observed engaging in calling tremulation. They oscillated their body vertically at a uniform rate for about 3s, paused about 7 Seconds, then repeated. After several vibration bouts they reverted to calling with airborne sound.

The pressure difference ear of tettigoniids conducts Sound from a permanently open acoustic stigma adjacent to the first thoracic spiracle, along the acoustic trachea, traversing the foreleg to the rear of the tympana. The unusual length of the limbs of M. macromelos has implications for the function of its auditory system: the extreme lengthening of the foreleg must affect the phase of externally and internally arriving Sound waves. And the tympana, being farther apart bilaterally, will subtend a larger than typical angle to the sound source. [1]

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