A silver spoon effect reduces lifetime fitness in a declining loon population.

A complete understanding of factors that influence animal fitness requires that we measure not only those occurring day to day in the life of an animal but also those that operate on longer time scales. Here, we investigated silver spoon effects (fitness impacts resulting from conditions faced early in life) and carryover effects (fitness impacts caused by environmental factors in a previous season) in a northern Wisconsin population of the common loon (Gavia immer). The mass of a loon chick divided by its age, an indication of food it received from its parents in its first 4 to 6 weeks of life ("chick condition"), affected both the likelihood of survival to adulthood and, among territory settlers, the number of chicks it fledged as an adult. Only one carryover effect was evident: increased ocean pH on the wintering ground had a modest positive effect on territory settlement rate. However, cohorts of loons that faced unfavorable ocean conditions in their first year yielded adults that fledged many chicks, which suggests that selection resulting from poor ocean conditions removed weaker phenotypes. The robust silver spoon effect in this species helps us understand a current and alarming pattern in the Wisconsin loon population: the sharp decline in the survival of chicks to breeding age.