Early recognition of offspring vocalisation by mink mothers

ABSTRACT: Mink deliver around the same time of year. Consequently, mink dams are exposed to other delivering dams and litters nearby in the same housing facility on farms. In addition, farmers often transfer kits between litters within the first week of life, as leveling large litters is believed to increase kit survival. It is, however, unknown whether farm mink mothers react to the exposure of unfamiliar offspring, or even are able to differentiate between own versus unfamiliar kits for instance based on vocalisations being particularly distinctive early in life. Therefore, I studied mink mothers (N = 18 second·parity brown, litter size 6 10 9; complete data sa: N = 16) behaviour towards playbacks or own versus unfamiliar kit vocalisations day 2 postpartum. Each dam was assigned  to a block of playbacks of offspring vocalisations recorded from individual male kits the previous day (postpartum day 1). The playback  loudspeaker – with a high linearity output in the range of 1-125kHz – was placed just outside the end of the home cage opposite to the nest box opening. Each dam was exposed to fixed orders of own and one unfamiliar male kit in call bouts of 1 min, controlled for order in the presentation or own and unfamiliar calls. Dam behaviour was recorded blind from video and data analysed taking repeated measures per dam into account. Dams reacted to the playback with approach, moving from the nest box with their litter into the wire cage closer to the source of the sound (time spent in wire cage: 69.1% with vocalisation,  14.2% when  silent, P  < 0.001), also spending more time in contact with the loudspeaker (39.8%) during kit vocalisation than when silent (0.3%; P  < 0.001). The time spent in the cage was negatively associated with the litter size (P = 0.035). The dams explored (touched, sniffed) the back wall area with  the loudspeaker for significantly longer time during the playback or her own kit (19.0 :: 2.11%) versus an unfamiliar kit (12.S :: 2.20%; P = 0.040). The dams contacted the loudspeaker area significantly quicker if the playback was their own kit (P = 0.016). The estimated hazard ratio for dam latency time to contact was 2.117 for own relative to alien kit playback. This preference – based on kit vocalisation postnatal days 1-2 – is the first evidence or mink mothers recognition of own compared to unfamiliar kits.