Biological and Environmental Drivers of Energy Allocation in a Dependent Mammal, the Antarctic Fur Seal Pup

Little is known about how variation in the pattern and magnitude of parental effort influences allocation decisions in offspring. We determined the energy budget of Antarctic fur seal pups and examined the relative importance of timing of provisioning, pup traits (mass, condition, sex), and weather (wind chill and solar radiation) on allocation of energy obtained in milk by measuring milk energy intake, field metabolic rate (FMR), and growth rate in 48 Antarctic fur seal pups over three developmental stages (perinatal, premolt, and molt). The relative amount of milk energy used for growth was 59.1% 8.1% during the perinatal period but decreased to 23.4% 15.5% and 26.0% 13.9% during the premolt and molt. This decrease was associated with a greater amount of time spent fasting, along with an increase in pup activity while the mother was at sea foraging. Average daily milk intake, pup mass, and condition were all important in determining how much energy was available for growth, but the amount of energy obtained as milk was the single most important factor determining pup growth. While mean mass-specific FMR did not change with developmental stage ( mL O2rangep1.74–1.77 /g/h), the factors that accounted for variation in FMR did. Weather (wind chill and solar radiation) and pup traits (mass and condition) influenced mass-specific FMR, but these impacts varied across development. This study provides information about the factors influencing how offspring allocate energy toward growth and maintenance and improves our predictions about how a changing environment may affect energy allocation in pups.