Development of leaps in dusky dolphin (Lagenorhynchus obscurus) calves

Leaping is a highly conspicuous behavior in cetaceans that may function in cooperative hunting and social bonding, thereby converging with forms of intra-specific communication present in other social mammals. However, few studies have analyzed the ontogeny of leaping, an important aspect in determining the adaptive significance of this behavior. The objective of our study was to quantify the ontogeny of leaping in dusky dolphins, a highly acrobatic species that engages in a variety of aerial displays. We tested the hypotheses that: (1) leap frequency changes with calf age, (2) frequency of leap type varies with calf age and (3) frequency of leap type varies by behavioral state. Data were collected off Kaikoura, New Zealand through boat-based group focal follows of nursery groups from October 2006 May 2007. We analyzed data from 73 nursery group encounters according to age category (young calf, yearling) and season (early, late). Early young calves leapt less frequently than late young calves (p < 0.01), but leap frequency did not appear to differ among older calves. Calves learned noisy leaps first, followed by clean leaps, then coordinated leaps, and finally acrobatic leaps as indicated by the positive correlations between week (i.e., calf age) and frequency of clean (p < 0.01), acrobatic (p < 0.01) and coordinated (p < 0.05) leaps. The relationship between behavioral state and frequency of leap type was not significant. These results indicate that nursery groups represent an important environment for healthy physical and social development of calves. Furthermore, while calves appear to learn the mechanics of leaping individually, they appear to learn the context in which the leaps are performed from conspecifics. This indicates that, as for other socially-complex mammals such as other cetaceans, primates, and social carnivores, social learning may be an important component in the ontogeny of dusky dolphin behavior.