Calling song (Figs 30, 31). The calling song of M. septa has a reeling or sweeping quality. This is due to the presence of slightly varying arrangements of syllable sequences, echemes and silent gaps. Close examination of song structure reveals that there are two subphrase types: a single echeme subphrase and a double echeme subphrase. These appear to interchange freely (and often unpredictably) during song production. The single echeme subphrases each comprise a sequence of 4–>10 syllables (syllables 0.01 s duration, gaps <0.01–0.08 s duration, decreasing successively; total duration of 0.09–0.43 s), followed by a long echeme (0.24–0.39 s) and a long gap (0.15–0.53 s duration) (all statistics, n = 19 recordings). Within each single echeme subphrase, the amplitude increased markedly during production of the echeme to a multiple of up to 3x the amplitude of the preceding syllable sequence. The double echeme subphrase commences in the same way as the single echeme subphrase except that following the long echeme there is a second, longer and higher amplitude, syllable sequence (with gaps between syllables initially 0.005–0.015 s duration, extending up to 0.03–0.07 s duration in mid sequence, then decreasing again towards the end of the sequence; 0.6–1.1 s total duration), followed by another echeme (0.25–0.43 s duration) and a long gap (typically 0.14–0.24 s duration). It is suspected that females would respond with a wing-flick signal to a calling male during the long gaps; however it is not known whether they respond at the end of each single echeme subphrase or each double echeme subphrase, or both.
This species calls during the day in warm, sunny conditions. The calling song maintains an even frequency distribution throughout, with a high amplitude plateau betwen 9.8 and 14.7 kHz and a dominant frequency of 10.5– 13.0 kHz. [1]