Bioacoustics of Ptenopus sceletus

Advertisement call. The advertisement call (Figs 3 , 20 J ) consists of 10 (8–13) notes uttered in slow succession, with a note rate of 2.60s - 1 (1.25–4.32). Note duration is short (28 ms [range 21–40]) and regular, note 1 duration deviance 8.7 % (range 0.5–16.2). The inter-note intervals may be very long (387 ms [range 204–661]), but are shorter and more regular at the beginning, then tending to longer intervals as the call progresses: Call starts fast, then slows down. Hence the inter-note interval range is usually high (102 % [range 26–163]). Median call density very low (28.3 [range 20.9–40.3]) and call duration is both long and variable ( 3.9s [range 2.5–7.2]). The basal frequency is 405 Hz (range 357–516) but very soft and usually inestimable, with harmonic bands louder towards the dominant frequency. The upper dominant frequency is at 4.3 kHz (3.8–4.8), and a clear (sometimes louder) lower dominant frequency is evident at around 2.0 kHz (1.4–1.9), usually less than half the upper dominant frequency. Frequency appears to remain constant throughout the notes and call, as is the case with the (human) perceived pitch, which is low and monotonous compared to most other species. Bandwidth (90 %) is difficult to estimate consistently, but is broad: approximately 0.3–6.9 kHz. The call appears to vary more than the calls of other species, except for P. carpi , with calls uttered late at night sometimes having only one to three notes. Call period (mean 365 s) varies greatly, but is usually lower than other species, and has not been recorded any shorter than 104 s during peak chorus activity. This species does not chorus as notably as most other species. Calls can be heard from after sunset to late at night. Seasonal phenology of calling activity is not known, but calls have been recorded in May and October. Calling activity is more pronounced on warmer evenings, but may continue despite cold, foggy conditions. As with other species, P. sceletus sp. nov. calls from the burrow entrance, although it may also call occasionally while roaming. This could not be observed directly, but a wandering gecko was often spotted in the area where a call was just heard – although wandering geckos are easier to detect than geckos in a burrow.

Natural history. The peak calling and breeding season of Ptenopus sceletus sp. nov. is probably between May and October (span of current call recordings), and juveniles have been found in November. This is slightly later than the apparent breeding season for P. carpi , but also coincides with months of somewhat lower fog incidence. This species does not call nearly as often as most congeners, but appears to spend more time wandering on the surface, even far from the burrows (as in P. carpi and P. adamanteus sp. nov. ). It is active much later into the night than most congeners, often only emerging well after dark, and its activity is not dampened by cold or foggy conditions (as in most other species). The burrow is usually shallower and simpler than those of other species, but may have two to three side-branches and typically has an escape exit (as in other species). As in P. carpi , it utters two different calls: The advertisement call and the single-pulse call, the latter usually uttered late at night after the main calling activity has ceased, and especially during dense fog.