Bioacoustics of Ptenopus maculatus

Natural history. Like the other species, P. maculatus males call from their burrow entrance and antagonistic behaviours between males are common if two burrow entrances are within ~ 2 m . Aggressors will sometimes utter the advertisement call as they look for the transgressing male, possibly to elicit a response. Males will increase calling frequency if a female approaches the burrow. Males may exit the burrow and approach the female, and after a brief encounter will follow the females into the burrow. Alternatively, the male will remain in place until the female scratches at the burrow entrance; the male then reverses into the burrow and the female follows. The male will utter a muffled version of the advertisement call inside the burrow, where copulation likely commences. After about an hour, the female will emerge partially from the burrow entrance, surveying the surrounding area with her head erect for a long time. This behaviour is repeated throughout the first night after a female moves into a new burrow, and its purpose may be to memorise the location of the new burrow entrance. Males presumably move out of the burrow after the female has moved in, as males and females have not been observed living in the same burrow.

Comment. Ptenopus maculatus was described from “ Damaraland ”, collected by Karl (= Charles) J. Andersson. This species was synonymised under the name ‘ P. garrulus ’ ( Boulenger 1885 ) . Subsequently, ‘ P. g. maculatus ’ was resurrected at subspecies level ( FitzSimons 1935 ), which has been regarded as valid ever since. Most of the earliest references to this subspecies, including the initial synonymisation with ‘ P. garrulus ’ (e. g., FitzSimons 1935 , 1937 b ; Loveridge 1947 ), referred to specimens included in our treatment of P. adamanteus sp. nov. and P. kenkenses sp. nov. , but exclude those from the type locality of ‘ P. maculatus ’. Mertens (1955) , Haacke (1975) , and several subsequent authors also referred to specimens from a broad geographic range, encompassing that of several species (current manuscript), as ‘ P. g. maculatus ’. According to Andersson’s notes and the location names used at the time (see map in Andersson 1855 and 1872), “ Damaraland ” referred to the Erongo Region in Namibia . Notably, Andersson stayed at “ Otjimbingue ” [Otjimbingwe] briefly in 1851 and again in the 1860 ’ s for several years, where this species occurs, and where it may have been collected. While staying here, a battle occurred on his property between the Damaras under chief Kamaherero, who had taken shelter at his house after fleeing their enslavement under the “ Namaqua ” (Nama) tribe Afrikaner, then under leadership of Christian Afrikaner (son of Jonker Afrikaner), leading to a victory by the Damara ( Andersson 1875 ). From the P. garrulus group species, “ Damaraland ” contains only P. maculatus sensu stricto (as presently treated). Additionally, the type specimens ( BMNH 1946.8.23.53 , 54) and a detailed drawing from the type description match the colour pattern and appearance of P. maculatus sensu stricto . Finally, the morphometric measurements of the BMNH types generally support this classification, and most unambiguously so for BMNH 1946.8.23.54 (Fig. 4 ). Hence, this specimen is assigned as the lectotype . We elevate the subspecies ‘ P. g. maculatus ’ to full species, thereby restricting the range of P. maculatus sensu stricto to the central and northern Namib Desert, north of the Kuiseb River (Fig. 5 ), and excluding P. adamanteus sp. nov. , P. kenkenses sp. nov. , P. circumsyrticus sp. nov. , and P. australis sp. nov. , from P. maculatus sensu stricto Haacke (1969) described the calls of P. maculatus sensu stricto and of P. circumsyrticus sp. nov. , from areas near Gobabeb (Central Namib Desert, Namibia ), but was unable to link individual specimens with their calls. Haacke (1969) also described calls of P. adamanteus sp. nov. as ‘ P. g. maculatus ’. The call of P. maculatus sensu stricto is described and distinguished in a standard taxonomic framework below.

Advertisement call. The advertisement call of P. maculatus (Figs 3 , 20 F typical call, 20 H Hoanib River population) consists of 6 notes (range 4–7, sometimes 8 in Hoanib River population) uttered in rapid succession, with a note rate of 4.99s - 1 (range 2.58–7.17). Note duration is long, 50 ms (range 26–71), with the first note being notably longer than the rest, note 1 duration deviance 138 % (range 39–274); the Hoanib River population has a relatively shorter first note than the typical call. The inter-note intervals are usually short (145 ms [range 88–303]) and regular with inter-note interval range 20 % (range 10–42), although the first interval may be slightly longer. Call density is higher than all other species, mean 0.36 (range 0.17–0.50). Call duration is short ( 1.1s [range 0.8–1.4]). The basal frequency is 380 Hz (range 301–517) but very soft and may be inestimable, with harmonic bands louder towards the (upper) dominant frequency at 3.4 kHz (range 3.0–3.8), while a clear but softer lower frequency peak is evident at around 1.7 kHz (range 1.4–2.0), just below half the (upper) dominant frequency. Frequency appears to modulate briefly up (~ 0.2 kHz), then drastically down by ~ 0.5 kHz with the first note, and less severely down in the notes following. The first note tends to be louder, have a slightly higher dominant frequency, and a slightly higher (human) perceived pitch than the following notes. Bandwidth (90 %) is difficult to estimate consistently: approximately 0.9–4.8 kHz. Call period (mean 110 s) varies greatly, but can be as low as 10 seconds during peak chorus activity. Calling commences shortly before or at sunset and may continue throughout the night after moonrise and before moonset. Calling activity is more pronounced around the austral spring and / or summer. Rainy weather usually causes calling activity to cease for days to weeks. This species rarely calls during the day.