Ultrasonic vocalisations of kits during maternal kit-retrieval in farmed mink, Mustela vison

Mink kits are born immature and are dependent on their dams’ protection, warmth and milk for survival. We hypothesize that vocalisations by mink kits may be of importance for communication between kit and dam, increasing the individual's chance of survival. However, very little is known about the nature and function of mink kits’ vocalisation. In the present study, we aimed to (i) describe the kit vocalisation, when it is placed away from warm nest/dam and littermates, (ii) investigate the influence of these vocalisations on maternal behaviour, in terms of dams orientation towards kit and kit-retrieval, and (iii) test whether active/stereotyping dams differed from less active/no-stereotyping dams in their kit-retrieval response. We used 58 first parity 1-year-old female mink of two genetic lines (colour type ‘Palomino’, n = 23, and ‘Black’, n = 35), allocated into equal-sized groups of active (including stereotyping) or passive (no stereotypic behaviour observed) individuals. All recordings were made during a standardised kit-retrieval test performed 5 days after birth. Our recordings demonstrated for the first time that mink kits are able to produce complex ultrasonic vocalisation with energy up to 50 kHz. The calls consist of long trains of multiharmonic pulses with a relative long pulse duration (average 264–874 ms) and a high repetition rate (0.6–2.3 pulses/s). The pulses contained most energy between 2.5 and 34 kHz (mean of Fmax and Fmin). Delayed maternal kit-retrieval increased the number of mink vocalisations (P = 0.007) but the repetition rate, average and S.D. in duration of pulses could not, in isolation, be identified as significant parts of the calls eliciting the maternal kit-retrieval response (P > 0.1). Genetic line affected both kit vocalisations and maternal retrieval since Palomino kits had a higher variation in pulse duration than Black kits (P = 0.023), and Palomino females had an impaired kit-retrieval compared to Black females (P = 0.008). We found no significant difference in kit-retrieval behaviour between groups of females according to their activity level. In conclusion, mink kits do produce ultrasonic vocalisation when isolated from their mothers and nests. Genetic and other factors influenced both (i) the nature of kit vocalisations (effects of colour type and litter size), and (ii) the maternal behaviour (effects of colour type and kit gender) during a standardised kit-retrieval test.