Use of photo-identification data to quantify mother-calf association patterns in bottlenose dolphins

For social mammals living in fission-fusion societies, the mother-infant bond is long and extends beyond the nursing period. We successfully developed a technique, using photo-identification data, to quantify mother-calf association patterns in a small population of bottlenose dolphins, Tursiops truncatus, off eastern Scotland. By statistically comparing association indices between young calves and their associates we assigned 17 individual adults as mothers to 20 young calves with a 5% level of probability. The mean index of association between calves and mothers remained high until at least year 8 of life. While calves were still found in the same schools as their mother, they surfaced beside her less often as their age increased. This is the first time that the mother-calf bond has been quantitatively assessed for any bottlenose dolphin population inhabiting temperate waters. Results are compared with those from subtropical populations and are discussed with respect to the viability of this population.