The behavioral development of two aquarium bottlenose dolphin calves, one male (born to a primiparous mother) and one female (born to a multiparous mother), was examined. From birth to 9 weeks of age, a total of 558.7 h of nursing and behavioral data were collected using focal sampling methods. Data from both calves revealed a pattern of increasing independence as they aged, but there were significant differences between the two calves. Suckling rates, mean suckles per bout, suckling bout rates, and bout durations for the male calf were higher than those for the female calf throughout the study. These frequencies declined significantly over time in the male's case but not in the female's case. Her suckling durations (lock-on time) were longer than his. The male spent more time in infant position (under the mother) than the female calf and less time swimming in echelon position (alongside the mother). Over time, the male spent less time in infant position, and the female calf spent more time socializing and less time echelon swimming. Both calves decreased the amount of time spent close to their mothers over the 9 week period, and the mothers decreased their role in proximity maintenance over time. We suggest that factors related to maternal primiparity caused the male calf to develop an effective compensatory response of frequent nursing and spending more time in infant position. Both calves survived and were healthy at the end of the observation period. © 1995 Wiley-Liss, Inc.