The energetic costs of lactation have been studied in many marine mammals, but little is known about the behavioral adjustments needed to cope with this event. By simultaneously measuring foraging behavior of lactating and nonlactating Antarctic fur seal females, we estimate the behavioral changes necessary to cope with the constraints of lactation and include the first comparative record of dive behavior between lactating and nonlactating female otariids. Nonlactating females exhibited highly variable foraging trip durations and spent long times onshore between trips. In contrast, lactating females exhibited consistently shorter trips and spent half the time hauled-out compared to nonlactating females likely to maximize offspring provisioning. Lactating females show a reduced mean time per dive but greater percentage of time per trip spent diving compared to nonlactating animals. The reduction in time onshore and trip duration, together with modifications in dive performance suggests additional effort of lactating females to compensate for the constraints of rearing a pup, which has not been observed previously due to the lack of simultaneous comparison of lactating and nonlactating individuals. When possible, future studies of maternal investment should also include nonlactating individuals, since lactation may have a strong synergistic effect with other aspects shaping foraging behavior.