Changes in the duration and frequency of foraging trips by female otariids may result in changes in the duration and frequency of lactation bouts and hence influence pup growth rate, unless females modify milk energy density and/or the total amount of milk delivered depending on the trip duration. To test this hypothesis on South American sea lions, we measured two attendance pattern components (foraging trip and haul-out duration) and three diving behaviour components of nursing females (dive time, bottom time and number of dives per h) at two different rookeries in Uruguay and Argentina, the composition and energy density of their milk, and the growth rate of their pups. Female foraging trip and haul-out durations depended on pup sex and weight, whereas milk energy density depended on female body mass and foraging trip durations. By contrast, the three dive variables were independent of female body mass or pup sex. Pup growth was also independent of the foraging trip and haul-out duration, with pup sex as the only significant variable. This suggests that individual differences in female foraging behaviour play a minor role in determining pup growth rates during the first three weeks after birth.