Cooperative Fish and Wildlife Research Units Program: Oregon
Education, Research and Technical Assistance for Managing Our Natural Resources

When provisioning chicks, parents make trade-offs toward allocating time, energy, and other resources to maximize reproductive success. As parents adjust investment to maximize their own fitness, impacts on offspring growth can occur. We investigated the relationships between provisioning (an index of parental investment) and chick growth of Adélie penguins Pygoscelis adeliae at a large, high latitude colony, where competition for food affects foraging effort and limits chick growth. We measured average amount of food delivered per day, quality of prey delivered, and foraging trip duration, and compared them to mass and skeletal growth rate of chicks during two breeding seasons of contrasting conditions. We used mixed-effects models to test the prediction that increased parental investment would lead to increased growth rates, while accounting for confounding effects of parent age, chick sex, year, brood size, hatching order, and the lack of independence between siblings. Little evidence indicated an effect of parent age. All measures of provisioning were important in predicting growth of at least one morphological character but, especially during the year of normal reproductive success, no measure of provisioning strongly or consistently predicted growth across a majority of morphological characters. However, during the difficult year a positive relationship existed between growth rates and parental investment, especially for male chicks — only the male chicks fed a high-fish diet grew as fast as the overall average male growth rate in the normal year. Growth of male chicks may be more sensitive to variation in parental investment, particularly under challenging conditions, and the results at least partially agree with theory about offspring-sex-based variation in parental investment. The observed variation in growth rates between males and females, and between years of contrasting apparent resource availability, was large enough to lead to size differences that may subsequently affect post-fledging survival and ultimately population processes.