Differences in Synchronous Behavior Between Bottlenose and Atlantic Spotted Dolphin Calves in the Eastern Gulf of Mexico.

Nancy J. Griffin

Mote Marine Laboratory, 1600 Ken Thompson Parkway, Sarasota, FL 34236

For dolphin mother/calf pairs, synchronous movement has implications for maintenance of social structure, affiliation and formation of stable relationships, safety from predation, foraging efficiency, and social learning. We coded behavioral events of bow riding focal pairs, derived from digital video segments, to compare synchronous, non-synchronous movement and behavior of Atlantic spotted (Stenella frontalis) and bottlenose (Tursiops truncatus) dolphins within shared continental shelf habitats. Positioning, proximity, group spread, breathing surfacings, spatial relations of calf, rates of synchrony and individual behaviors were analyzed, with Chi Square analysis and 2-factor ANOVA. Calf size classes were estimated from measurements of still photographs, derived from digital videotape (Class 1=<70%, Class 2=>70% mother's length). I found significant (p<.05) behavioral differences between bottlenose and spotted dolphins and between size classes within each species. Spatial relations of spotted dolphin calves relative to mothers significantly differed between classes, with larger spotted calves bow riding in P1, (calf and mother parallel, rostrums aligned) and smaller calves in P2, or echelon (calf close to mother's flank above midline). Initiation of synchrony by smaller spotted dolphin calves differed between species, and by size classes; and calves of both size classes terminated synchronous movement more frequently than mothers. Smaller bottlenose calves were more likely to break synchrony than larger calves. Larger bottlenose dolphins synchronously surfaced more frequently than smaller dolphins. Significant differences in synchronous movement for both classes of spotted and bottlenose dolphin calves suggest apparent differences in odontocete social systems. Synchronous behavior in calves may provide protection or facilitate learning in close proximity with mother. Differences in ecology, such as variation in predation risks or home range size, may select for behavioral responses, which may differ between species in open systems. Future work will refine a new analytical technique with real time data derived from focal follows, in concert with videotape analyses.