The development of suckling behaviour in two captive- born calves of bottlenose dolphin (Tursiops truncatus)

Few and contrasting results have been obtained on nursing patterns of newborn and infant dolphin calves, so that the developmental profile of this behavior is still largely unknown. The aim of the present study was to observe, from birth to one year of age, the development of suckling behavior of two calves of Tursiops truncatus that were born three weeks apart in the same aquarium. Duration, frequency, lateralization, and day/night patterns of attempted (AS) and successful (SS) suckling episodes were scored. Observations followed this rationale: a) 1st week: 20 hours/day; b) 2nd-8th week: 20 hours/week; c) 9th-16th week: 20 hours/2 weeks; d) 17th-52nd week: 20 hours/3 weeks. Overall, the ontogenetic profile were rather similar in the two calves, and greater age-related changes were observed during the earlier compared to the later developmental period. AS frequency was high in the first postpartum phase. It readily decreased to very low levels thereafter, when SS frequency sharply increased, so that by the third day of life the correct behavior had almost totally replaced the attempts. SS duration increased over the first few days of life, and showed what appeared as a phase of adjustment around the second month. A circadian pattern was found during the first week of life for successful suckling, whose frequency and duration were higher during the night than during the day time. As for the last months of observation, individual developmental trends of suckling frequency were fairly consistent with the different time-courses of weaning. Finally, no definite evidence for a nipple preference appeared.