Ultrasound from underground: cryptic communication in subterranean wild-living and captive northern mole voles (<i>Ellobius talpinus</i>)

This study provides the first evidence of ultrasonic vocalisations (USVs) in a truly subterranean rodent, the northern mole vole <i>Ellobius talpinus</i>. Calls were recorded by attracting callers with a bait to burrow entrances, where they were mostly visible to researchers. USVs recorded from 14 different burrows in southern Russia were verified as belonging to <i>Ellobius talpinus</i> by comparison with USVs of two wild-captured young males and by comparison with USVs of four adults from a captive colony. As a first attempt at exploring the function of USV diversity, we defined upward-intense USVs, with a maximum fundamental frequency (f0) of 35.32 ± 5.11 kHz, and variable-faint USVs, with a maximum f0 of 31.40 ± 7.78 kHz. Compared to variable-faint USVs, the upward-intense USVs were longer, had a larger depth of frequency modulation and were produced at high intensity in regular series. The upward-intense USVs were lower in the maximum and peak frequencies in the wild than in captivity, whereas the variable-faint USVs did not differ between recordings from the wild and from captivity. We discuss that similar ranges of acoustic variables found in USVs of <i>Ellobius talpinus</i> and surface-dwelling Arvicolinae species do not support the hypothesis that subterranean life has drastically reduced ultrasonic vocalisation in rodents.