Maternal age influences growth efficiency and offspring behavior during provisioning in northern elephant seals (Mirounga angustirostris)

Offspring of capital breeders, such as the northern elephant seal (Mirounga angustirostris), are nursed exclusively from maternal body reserves. Energy expenditure available for lactation is limited by the amount of body reserves females acquire prior to parturition. Despite efforts to understand the influence of maternal traits, (e.g. age, size, body condition) on reproductive effort, much less is known about how maternal traits and environment influence the behavior of offspring and ultimately, how offspring behavior may influence the efficiency of the translation of maternal investment into offspring growth and energy storage. Milk energy intake and offspring storage data (n=38) suggest impacts of maternal age on growth efficiency that are independent of rates of energy delivery. To determine the mechanisms underlying this effect of maternal age, behavioral data were collected from pups of 46 known-age females, from parturition to weaning, across six years and three different sites along the Central California Coast, representing 3954 seal-hours of observation. Pup behaviors were divided into five mutually exclusive categories that potentially impacted pup energetics. Pups of older females spent more time resting, while pups of younger females spent more time locomoting and distant from their mother. Pups spent more time suckling and locomoting and less time resting as they developed. Pup behavior showed strong diel patterns with activity decreasing over the day. The magnitude of these relationships varied between rookeries, suggesting influences of harem topography and environmental features on pup behavior. Together these findings suggest direct impacts of maternal breeding experience on pup behavior and, ultimately growth efficiency.