Abstract: This investigation focused on the underwater behaviours and development of free-ranging Atlantic spotted dolphin (Stenella frontalis) mothers and calves in the Bahamas. During summer field seasons from 1991 to 2000, underwater video recordings were collected as part of a long-term life history and behaviour study. From these video recordings, sequences with a 3 min total observed time of both the mother and calf were analysed. Video segments were analysed for 10 mother/calf pairs of each calf age category (i.e., years one, two, and three), for a total of 30 mother/calf videos, and 10 additional videos of 4-year-old calves were also analysed. Frequency of behavioural events were compared: between (1) calf age categories, (2) mothers of calves in each age category, (3) calf age categories related to proximate associate, and (4) calf age categories related to the synchronicity or asynchronicity of the behaviours. Results demonstrated an increase in calf independence in year four shown by a significant reduction in nursing acts, significantly more feeding/foraging, and increased behaviours performed in the proximity of individuals other than the mother or increased time spent alone. Mothers exhibited no strong evidence for increased maternal rejection behaviours near the end of the estimated nursing period. For select behaviours, synchronicity increased with calf age. This study is rare in its ability to analyse the underwater behaviours of free-ranging dolphins and aims to reveal a strategy for non-invasive research as well as increase our understanding of the life history aspects of this species.
Key Words: ATLANTIC SPOTTED DOLPHIN; STENELLA FRONTALIS; BEHAVIOUR; DEVELOPMENT; CALVES; FREE-RANGING; UNDERWATER
Document Type: Research article