Infant carrying behaviour in dolphins: costly parental care in an aquatic environment

1. Infant carrying behaviour occurs across diverse taxa inhabiting arboreal, volant and aquatic environments. For mammals, it is considered to be the most expensive form of parental care after lactation, yet the effect of infant carrying on the energetics and performance of the carrier is virtually unknown. 2. Echelon swimming in cetacean (dolphin and whale) mother-infant dyads, described as calf in very close proximity of its mother's mid-lateral flank, appears to be a form of aquatic 'infant carrying' behaviour as indicated by the hydrodynamic benefits gained by calves in this position which enables them to maintain proximity of their travelling mothers. Although this behaviour provides a solution for minimizing separations of mother-infant dyads, it may be associated with maternal costs. 3. Through kinematic analyses this study demonstrates empirically that 'infant carrying' impacts the locomotion of dolphin (Tursiops truncatus) mothers as evident by decreased swim performance and increased effort. 4. The mean maximum swim speed of mothers swimming in echelon only represented 76% of the mean maximum swim speed of these mothers swimming solitarily. In addition, there was a concomitant 13% reduction in distance per stroke for mothers swimming in echelon compared to periods of solitary swimming. 5. Thus, 'infant carrying' in an aquatic environment is associated with maternal costs, and could ultimately impact maternal energy budgets, foraging efficiency and predator evasion.