Advertisement call. Advertisement calls of Spinomantis beckei were recorded on 28 January 2005 at Andohahela National Park at approximately 1650 m a.s.l. at an air temperature between 15–20°C (seven calls with a total of 57 notes of one individual recorded). The recorded calls were emitted either by the holotype or the paratype (insufficient field notes taken) at apparently regular motivation. Specimens were calling in the late afternoon before dusk, during a period of very heavy rains caused by a cyclone passing. This recording was incorrectly assigned to S. bertini by Vences et al. (2006: CD2, track 57).
Calls (Fig. 5) have a duration of 430–1278 ms (696 + 313 ms) and consist of a series of 6–13 (8.5 + 3.1) short notes, with each note represented by one single pulse. Calls are somewhat complex in structure due to different kinds of modulation involved. Initial notes (i.e., those excluding the terminal note[s] with maximum amplitude) are very short with a duration of 5–13 ms (8.4 + 2.9 ms) and are emitted at intervals of 50–89 ms (63 + 11 ms) duration at an approximate repetition rate of 13–14 notes/second. Initial notes are followed by 1–2 terminal notes of longer duration of 20–26 ms (23.6 + 1.9 ms), which are separated from initial notes by longer inter-note intervals of 163– 195 ms (172 + 11 ms), but are generally identical to initial notes in overall structure. Terminal notes exhibit the highest amplitude of all notes of a call, with the amplitude almost constantly increasing in series of short initial notes. However, the increase in amplitude from the first to the last note is slightly irregular in some calls. In addition to the amplitude modulation present within calls, there is also slight frequency modulation among notes, with the first note exhibiting the lowest dominant frequency with 4016–4317 Hz (4095 + 124 Hz), increasing towards the last of the short initial notes with 4468–4790 Hz (4670 + 133 Hz). The longer and more powerful terminal note of each call then slightly drops in dominant frequency with 4297–4467 Hz (4379 + 54 Hz), with this frequency representing the overall dominant frequency of the entire call. The approximate prevalent bandwidth of the call is 3400–6700 Hz. Calls were emitted at an approximate rate of 30 calls/minute, with inter-call intervals ranging from 840–1690 ms. The combination of different note lengths, amplitude modulation and frequency modulation results in a very particular and easily recognizable sound of the call.
In comparison, calls from the type locality of S. bertini recorded at 21°C air temperature at Isaka-Ivondro, Andohahela, described and illustrated by Andreone & Randriamahazo (1997), differ by the lack of longer terminal note(s), distinctly lower note repetition rate (7.3 versus 13–14 notes/second) and absence of or less distinct frequency modulation among notes within a call. However, note duration and bandwidth seem to overlap (no recording available to us for detailed comparison).
Calls of an undescribed candidate species of the Spinomantis bertini complex (S. sp. Ca7; Vieites et al. 2009; Perl et al. 2014) from Mount Maharira, Ranomafana National Park (Vences et al. 2006: CD2, track 58, as Spinomantis aff. bertini), mainly differ from calls of S. beckei by a lower number of notes per call (3–4 versus 6– 13), shorter call duration (293–400 versus 430–1278 ms), notes consisting of several pulses (versus single pulse only), and a slight decrease of frequency of notes within a call (versus distinct increase of frequency).