Parental physiological condition and reproductive success in chinstrap penguins (Pygoscelis antarctica)

Recent studies suggest that parental resource allocation may be the most important factor explaining differences in reproductive output among parents. That said at least two different hypotheses of balance between parental foraging effort and resource allocation have been proposed. First, parents with high foraging effort have high reproductive success. Second, parents with higher allocation of resources to offspring have high reproductive success. We tested the second hypothesis using chinstrap penguins (Pygoscelis antarctica) as a model. We evaluated nutritional condition of the parents using blood urea, uric acid, creatine kinase, and cholesterol levels. We evaluated reproductive success according to total mass of the brood and asymmetries inside the brood. We measured the degree of asymmetry using weight and culmen length. Generalized linear models were used to examine relationships between adult plasma urea levels with year, nest position, and degree of asymmetry in chicks. Our results demonstrate that lighter broods were more asymmetric and associated with lower values of adult plasma urea, uric acid, and creatine kinase. We interpret these findings as evidence that the birds allocate fewer resources to their chicks than adults with more symmetric broods are.