Pre- and Postpartum Acoustic Activity in Captive Pacific White-Sided Dolphin (Lagenorhynchus obliquidens) Mothers

Active acoustic emission from a mother to a calf after parturition is one strategy used to enhance recognition of mothers by calves and develop, then maintain, a mother–calf bond from an early stage. This study predicted that a high-calling postpartum period exists in a social delphinid, the Pacific white-sided dolphin (Lagenorhynchus obliquidens). This species produces pulsed call sequences for vocal exchange with conspecifics, and these sequences appear to be an important signal between mothers and calves. Sounds were recorded from three pregnant females at the Niigata City Aquarium, Marinepia Nihonkai, Japan, before and after each birth in 2019, 2020, and 2021 to investigate the rate of their pulsed call sequences. Continuous data from prior to four days to five days following parturition, opportunistic data within the last pre-parturition month, and data from the postpartum period were obtained from the females. The pulsed call sequence gradually increased during the last gestational month. A high-rate sequence was repeated daily for four days pre-parturition and faded within several hours postpartum, and few sequences were produced from the day after parturition. Contrary to our prediction, the many pre-parturition sequences and fewer postpartum sequences suggest a low efficiency of postpartum imprinting in this species.