Bioacoustics of Kalophrynus minusculus

Kalophrynus minusculus has an overlapping body size with K. eok Das & Haas and K. punctatus Peters , but can be differentiated from those species by the presence of inguinal spot in most specimens (vs. absent). Additionally, K. minusculus differs from K. eok and K. punctatus by having several dark stripes near groin and side of the body [vs. absent: Das & Haas (2003), Inger (1966) ]. Kalophrynus minusculus also has an overlapping body size with K. heterochirus Boulenger , K. honbaensis , K. limbooliati , and K. yongi Matsui. However , it can be differentiated from these species as follows: from K. heterochirus and K. limbooliati by a portion of the fourth finger projection from the palm longer than the terminal phalange of the third finger (vs. shorter); additionally, K. minusculus differs from K. heterochirus by the presence of a black inguinal spot (vs. white-bluish). K. minusculus differs from K. honbaensis by the absence of finger webbing [vs. present: Vassilieva et al . (2014) ]; and from K. yongi by the absence of nuptial pad (vs. present). Call characteristics. An adult male (unvouchered specimen) of Kalophrynus minusculus was captured in Kampung Cikawung , Ujung Jaya village , Sumur district , Pandeglang Regency , Banten Province ( -6.800636 , 105.499069 , 8.8 m a.s.l) on 08 April 2025 and brought to a room. Although the specimen was not preserved as a voucher, its identification was confirmed based on direct morphological examination. We recorded one call of one adult male ( Fig. 7 ) at distances of approximately 1 m at an air temperature of 28.0° C. The call sounds to the human ear like “krek….krek…….krek” with a duration of call 1.14 s and dominant frequency 516–689 Hz (mean 617 ± SD 84.685). Note series consist of 3 notes, with two pulses, duration of note series 0.031 −0.048 s (mean 0.040 ± SD 0.008), pulse duration 0.007 −0.026 s (mean 0.015 ± SD 0.007), inter-pulse interval 0.001 −0.022 s (mean 0.010 ± SD 0.011), pulse period 0.023 −0.029 s (mean 0.026 ± SD 0.003), and pulse rate 34.596 −43.774 s (mean 38.380 ± SD 4.796). Call comparisons. The call characteristics of 11 species of Kalophrynus have been described, analyzed, and recorded [ K. meizon : Matsui et al . (1996) ; K. baluensis : Malkmus & Riede (1996) , Inger et al . (2017) ; K. yongi : Matsui (2009) ; K. barioensis : Matsui & Nishikawa (2011) ; K. calciphilus : Dehling (2011) ; K. cryptophonus : Vassilieva et al . (2014) ; K. interlineatus : Matsui et al . (1996) , Ohler & Grosjean (2005) ; K. limbooliati : Matsui et al . (2012) ; K. dringi , K. nubicola , K. puncak : Inger et al . (2017) , Fukuyama et al . (2021) ]. The call of Kalophrynus minusculus differs from K. baluensis , K. barioensis , K. limbooliati , K. meizon , and K. yongi by the well-pulsed note (vs. unpulsed note). The call of K. minusculus differs from K. cryptophonus , K. dringi , K. interlineatus , K. nubicola , and K. puncak by consisting of a series of notes (vs. a single note). Additionally, the call of K. minusculus differs from K. cryptophonus by having a lower dominant frequency, 516−689 Hz (vs. 900−1200 in K. cryptophonus ). The call of K. minusculus differs from K. calciphilus by having two pulses (vs. consisting of only 7 or 8 pulses). Tadpoles. Unknown.