Bioacoustics of Ewartia etesia

Distribution and habitat . Ewartia etesia n. sp. is restricted to the Top End of the Northern Territory , with the exception of a single record from El Questro Station, in the Kimberley region of north-east Western Australia . In the Top End it has been found from Litchfield National Park east to Maningrida and south to the Mataranka district ( Fig. 25 ). Populations occur in association with wattles, including Acacia lamprocarpa and A. latescens . Adults have been collected between October and February. Calling song . The complex calling song mode of E. etesia n. sp. ( Figs 26 , 27 ) contains repeated, short subphrases (0.45– 0.67 s duration; all statistics n = 16). Each subphrase is composed of a brief syllable sequence (0.360– 0.460 s duration) in which the gaps between syllables (initially 0.034– 0.061 s duration) sequentially reduce until the syllables (each 9–12 ms duration) coalesce into a macrosyllable (4–9 syllables, 0.038– 0.093 s duration) or an echeme (0.101– 0.161 s duration). The placement of the accentuation in this species is subtle. It occurs at the end of some subphrases after the macrosyllable or echeme in the form of a series of 1–3 discrete syllables, each followed by a gap (0.061– 0.083 s duration) (e.g. Fig. 27 ). This calling song mode is typically produced at intervals throughout the day. The transition between calling song modes in this species may be unusually protracted, whereby the complex calling song suddenly becomes disjointed. This is due to the following: (1) the syllable sequence preceding each echeme is truncated into 1–3 syllables, (2) the macrosyllables stop being produced, and (3) a series of 3–4 discrete syllables (some of these may be double syllables) produced following each echeme. The song then undergoes further reduction of syllables surrounding the echeme and morphs into the simple calling song. In some cases, this transition may be so gradual that it is hard to detect definitively. Once fully formed, however, the simple calling song mode of this species is, nevertheless, quite distinct from the complex mode. The simple mode ( Fig. 28 ) contains monotonously repeated phrases (0.54– 0.62 s duration). Each phrase is composed of 1–3 syllables (each 0.009– 0.012 s duration), each separated by gaps of successively reducing duration (each 0.005– 0.024 s ), which is then followed by an echeme (0.143– 0.261 s duration). Sometimes the echeme is followed by a gap (0.014– 0.081 s duration) and then another 1–4 syllables and /or macrosyllables (each 0.009– 0.030 s duration; intervening gaps 0.007– 0.085 s duration). A final gap (0.116– 0.296 s duration) completes the phrase. This calling song mode predominates at dusk and is also occasionally produced during the day. As per other species in the Ewartia oldfieldi species complex, in E. etesia n. sp. the calling song frequency spectra do not change between song modes. In each mode the calling song typically has a highest amplitude frequency plateau between 10.0 and 15.7 kHz, with a dominant frequency between 11.8 and 13.6 kHz (mean=12.6, n=13; Figs 29 A, 29B).