Ultrasound from underground: cryptic communication in subterranean wild-living and captive northern mole voles (Ellobius talpinus

This study provides the first evidence of ultrasonic vocalisations (USVs) in a truly subterranean rodent, the northern mole vole Ellobius talpinus. 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 Ellobius talpinus 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 Ellobius talpinus and surface-dwelling Arvicolinae species do not support the hypothesis that subterranean life has drastically reduced ultrasonic vocalisation in rodents.