Abstract
Hipposideros khaokhouayensis is a globally rare and vulnerable species. Since information about its distribution and echolocation was very limited, the author conducted a series of bat surveys in northwestern Vietnam with an emphasis on this species between 2022 and 2023. Bats were captured using harp traps and mist nets then identified in the field based on their morphological diagnoses. Echolocation calls were recorded under three different situations (free-flying while emerging from caves, handheld, and flying within a flight tent) using the PCTape system. A colony of the species was discovered in Son La Province. The adults of this colony were found to be considerably larger than all individuals described in previous publications. The species emits multiharmonic calls with the most energy in the second harmonic. Each usual call comprises two components: a constant-frequency (CF) component followed by a downward frequency-modulated terminal sweep (tFM). Special calls, which were not mentioned in any literature, were recorded in-between usual calls. Each special call comprises three distinct components: an upward frequency-modulated initial sweep (iFM) followed by a CF and a tFM. The frequency of the CF component and the pulse duration of the adult bats from Son La Province are higher and longer than those in published descriptions. The present study results indicate that H. khaokhouayensis emits a single call or calls in groups up to seven signals. The new distributional record, morphological features and echolocation characteristics demonstrated herewith, provide essential information for monitoring and conservation of this vulnerable species at national and international scales.