Suckling behavior and its development in two Yangtze finless porpoise calves in captivity

We focally observed the suckling behavior of two Yangtze finless porpoise calves, C05 and C07, in captivity. Between 15 and 730 days postpartum of C05 and between birth and 30 days postpartum of C07, 286.3 (1.9 ± 0.4 hr/day (mean ± standard deviation), n = 148 days) and 18.3 hr (2.0 ± 0.5 hr/day, n = 9 days) of video footage were recorded, in which 429 and 111 suckling events were observed, respectively. We found that the calves made their initial suckling attempts after repeated stroking of the mother's body with their rostrums. The suckling duration was 4.4 ± 1.8 sec and 4.8 ± 2.4 sec, respectively. Before suckling, the calves swam under the mother's genital region (99.1% of number of event, respectively). During suckling, the mother generally turned sideways to facilitate the calves' suckling (80.7 and 76.6%, respectively). The calves almost equally used the two mammary slits [52.2% (left) and 47.8% (right), and 44.1% (left) and 55.9% (right), respectively]. The frequency and proportion of time C05 spent suckling continuously decreased to zero by 483 days postpartum. The two variables for C07 increased following birth, to a peak at 16 days postpartum, and then decreased continuously until 30 days postpartum. We discuss the possible implications of these observations for the management and conservation of this endangered cetacean.