Distribution. South-eastern part of European Russia, Siberia, northern and eastern Kazakhstan, Mongolia, northern China.
Material. 18. Russia, Altai Republic, ab. 26 km SE of Ongudai, environs of Kupchegen’, 50°37.3’ N, 86°26.2’ E, 922 m a.s.l., 08.08.2017, song recordings in 3 ³.
References to song. Bukhvalova & Zhantiev, 1994: recordings from Tyva, calling song; Benediktov, 2005: recordings from southern Siberia, calling song.
Song. The courtship song of Ch. dubius starts as an echeme similar to the calling song but lasting longer, up to 20 s. The echeme begins quietly, reaching maximum intensity in about 8–10 s (element 1, Fig. 12 A). The element 1 contains syllables repeated at the rate of about 6–7/s. The hind legs are almost synchronously moved up and down. During the gradual up-stroke the legs produce a soft noisy sound, whereas during the stepwise down-stroke the legs generate 5–6 loud pulses (Fig. 12 D). This echeme can be repeated one-two times, and then 5–10 loud syllables of another temporal structure immediately follow (element 2, Fig. 12 C, E). They are repeated at the rate of about 13/s. In contrast to the element 1, the syllables of the element 2 are produced by gradual up- and down-strokes and do not contain distinct pulses. In about middle of the element 2, a male generates one high-amplitude stroke with the hind legs producing a syllable of dense pulses. The two elements can be repeated two–three times. The dominant frequencies of the spectrum lie between 20 and 40 kHz. The frequency spectrum of the element 1 has five clear harmonics in this band (Fig. 12 F), whereas the harmonics are not so obvious on the spectrum of the element 2 (Fig. 12 G).
Comparative remarks. The courtship song of Ch. dubius has been recorded for the first time.