(Figs. 11, 12)
Robillard et al., 2014: 12; Dong et al., 2018: 6 (molecular phylogeny); Cigliano et al., 2019 (Orthoptera Species File).
Material examined: Malaysia, Sabah, Sandakan, Rainforest Discovery Centre, 1 female (SDK.19.6), N5.87410, E117.94366, 50.2± 5.1 m.a.s.l., 8 January 2019, 2102 hours, on foliage, coll. M. K. Tan & S. T. Toh (ZRC); 1 female (SDK.19.21, Fig. 11A) N5.87542, E117.94231, 31.1± 4.8 m.a.s.l., 9 January 2019, 1930 hours, on foliage, coll. M. K. Tan, R. Japir, Momin Binti & J. Y. Lee (FRC); 1 male (SDK.19.36, Figs. 9 B–9D), N5.87547, E117.94110, 34.1± 5.4 m.a.s.l., 9 January 2019, 2046 hours, under foliage calling, coll. M. K. Tan, R. Japir, Momin Binti & J. Y. Lee (ZRC).
Calling song (Fig. 12): At 28.4°C and RH 74%, the calling song of C. borneoe consists of doublets (or rarely triplets) of long syllables including strong amplitude modulation forming pulse-like structures. Echemes (doublet) last 660 ± 75 ms with a period of 3.5 ± 1.2 s. Within doublets, syllables last 196 ± 43 ms, with a period of 372 ± 47 ms. Dominant frequency value is 17.6 ± 0.4 kHz with no clear harmonic structure.
Habitat and life history traits. C. borneoe inhabits the dipterocarp forest in Sandakan and is typically found on or under the foliage of tree sapling or shrub at night.
Remark. The calling song of C. borneoe differs from that of Cardiodactylus admirabilis Tan & Robillard, 2014 from Singapore by consisting of doublets with longer echeme duration (instead of triplets with shorter echeme duration of 205.6 ms) and higher dominant frequency (instead of 14.3 kHz). This is despite of the similarities in the morphology and genitalia of these two species. Another morphologically similar species is Cardiodactylus thailandia Robillard, 2011 from Thailand but its song is unknown.