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. |