Notes on Xenorhina bouwensi

Morphometrics. Xenorhina bouwensi was described (as Pseudengystoma Bouwensi) by de Witte in the year 1930 on the basis of a single specimen collected in the Arfak Mountains (Vogelkop Peninsula) of western New Guinea. This species was redescribed by Zweifel (1972) who examined the holotype as well as various specimens from the Sibil Valley about 500 miles east­southeast of the type locality. As Zweifel (1972) recorded only a few measurements of the holotype, some additional ones should be given here (in mm): SUL 19.0, TL (RG) 8.6 (according to Zweifel´s method 7.6), TaL 4.4, T4L 8.7, T4D 0.5, T1L 1.5, MTL 0.9, F3D 0.25, HL 5.2, HW 7.0, SL 2.1, END 1.6, IND 1.6, ED 1.6, TyD 1.1, OD 4.3; TL/SUL 0.45 (according to Zweifel´s method 0.40); TaL/SUL 0.23; T4L/SUL 0.46, T4D/SUL 0.026, T4D/F3D 2.0, MTL/T1L 0.60, HL/SUL 0.27, HL/HW 0.74, END / IND 1.0, ED/SUL 0.084, TyD/ED 0.69, SL/SUL 0.11, OD/SUL 0.23.

A total of 17 Xenorhina bouwensi specimens were collected by the senior author and his helpers in the Wondiwoi Mountains at the base of the Wandammen Peninsula in the years 1998–2003. Among them were 11 adult males (Fig. 1), three adult females and three juveniles. Snout­urostyle­length of the juveniles was from 7.4–11.5 mm, that of adult males from 16–22 mm (mean 19.5 mm, SD 1.6) and that of adult females from 18.0– 20.7 mm (mean 18.9 mm SD 1.5). There are no significant differences in total size or body ratios between sexes, therefore the ratios of all 14 adult specimens could be summarized (Table 1). Comparisons between the holotype and the present series from the Wondiwoi Mountains yielded only some small differences. Therefore, we are fairly sure that both belong to the same species. For morphological details of Xr. bouwensi see its redescription by Zweifel (1972).

Ecology and behaviour. The natural habitat of Xr. bouwensi is primary rain forest between 400 and 800 m a.s.l. on the eastern slopes of the Wondiwoi Mountains near the base of the Wandammen Peninsula (Cenderawasih Bay). Almost all specimens were detected when they were calling from below the surface. Most calling sites were in small cavities 5–20 cm deep between small roots and soil and juveniles and females were also found in subterranean retreats. Only a few specimens were encountered on the surface in leaf litter. In some cases individuals stayed rather close together. For example a calling male and a juvenile of 7.4 mm SUL were found in a distance of only 25 cm from one another on 7 May 2000. Very often neighbouring males were calling antiphonally, but sometimes also exactly synchronously. The advertisement calls are series of musical notes sounding like uup­uup­uup…. These series last from a few seconds up to two minutes, the same applies to the intervals between series. Notes can be uttered in continuous series or series may be interrupted by short breaks. The mean rate of notes during 194 seconds (s) calling time of three specimens was 1.9 notes/s. The lowest rate was 1.5 and the highest was 3.2 notes/s. Note length was about 90 milliseconds (ms) in all three males, internote intervals varied considerably. Two specimens with a mean interval duration of 475 and 495 ms showed no significant difference in this trait while the third specimen with a mean interval length of 315 ms differed significantly from the others. Usually notes start suddenly with a maximum sound intensity. Loudness drops markedly and continuously to the end of notes (Fig 2 a). The audiospectrogram exhibits a dominant and clearly tuned frequency band around 1.0 kHz and one upper harmonic band around 2.0 kHz (Figs 2 b and 2c). There is a weak downward modulation of the frequency.

The stomach of one male contained two earthworms (4 and 9 mm long), one dipteran larva and two heads of very small ants.

A female of 20.7 mm SUL had only two fairly well developed eggs (diameter about 1.3 mm) in its ovaries, all other eggs were much smaller.