Early vocal development of Eurasian lynx cubs (Lynx lynx) before and after leaving the natal den

Abstract We investigated the ontogenetic development of vocal repertoire in cubs of the Eurasian lynx Lynx lynx from birth until 3 months of age. Calls of four litters of captive lynxes kept in large outdoor enclosures were recorded within natal dens and during activities near the dens automatically and manually. We confirmed early findings that Eurasian lynx cubs are capable of producing biphonic calls with two independent fundamental frequencies in call spectra, the low (f0) and the high (g0), potentially created with two different sound sources. In the vocal repertoire of cub Eurasian lynxes, we subdivided 3 structural classes, which included in total 10 call types. The structural classes were classified based on presence/absence of one or two fundamental frequencies: two low-frequency call types with f0-singly, four high-frequency call types with g0-singly, and four biphonic call types with both f0 and g0. The f0 ranged from 0.17 kHz to 1.19 kHz, the g0 ranged from 0.21 kHz to 7.19 kHz among different call types. All the 10 calls types were present in Eurasian lynx cubs starting from the first week of age; no one of these call types disappeared to 3 months of age and no additional call types appeared to this age. Assignment the calls to the predicted call type with discriminant analysis was 94.5% for the low-frequency calls, 89.3% for the high-frequency calls, and 67.8% for the biphonic calls, thus suggesting robust classification. Acoustic parameters of both f0 and g0 frequencies decreased with age. We discuss the ontogeny of g0 in biphonic calls of mammals and the high acoustic complexity of vocal repertoire of Eurasian lynx cubs in relation to evolution of vocal traits across the studied Felidae species.