Conocephalus (Anisoptera) fuscus (Fabricius, 1793)

The calling song, produced during the day-time, consists of long echeme-sequences lasting up to 4 minutes or more. The sound is faint, with a rustling or sizzling quality. Oscillographic analysis shows the sequences to consiust of trisyllabic echemes with a highly characteristic pattern. The first two syllables of each echeme consist of short opening hemisyllables followed by longer closing hemisyllables; the first diplosyllable lasts about 12-21 ms and the second, following a very short gap of 1-3 ms, is usually very slightly shorter (11-20 ms). There is then a longer gap, usually 3-13 ms, followed by the third syllable, again usually a diplosyllable but lasting longer than the first two, about 17-30 ms. Occassionally the third syllable lacks an opening hemisyllable and may thenlast for as little as 12 ms. The whole echeme lasts about 45-80 ms and successive echemes are separated by an interval of about 10-20ms; the echeme repetition rate is about 10-16/s. The hemisyllable at the beginning of each echeme id often particularly prominent.

Some of the songs studied consisted only of uniform echeme-sequences of this kind (Figs 147-151), but most included short periods (usually 0.3-2.0s, rarely up to 6.0 s) of a 'ticking' sound consisting of identical syllables repeated at the rate of about 20-30/s. These were usually diplosyllables lasting about 15-25 ms, but occassionally the opening stroke was silent, leaving a closing hemisyllable lasting about 8-20 ms. These short periods of ticking were sometimes very widely spaced so that they were hardly noticeable, but in about a third of the males studied they occurred much more frequently, someties every few seconds dutring at least part of the song. (Figs 152-154). At such times the song sounds superficially like the calling song of C. dorsalis, and oscillographic analysis (or speed reduction of a recorded song) is neccessary to show that the echemes in the main part of the song are trisyllabic, unlike the tetrasyllabic echemes of C. dorsalis [= fuscus]. Occassional short bursts of ticking are probably a normal component of the calling song of C. discolor, although such bursts are much less prevalent than in C. dorsalis. [1]

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