Juvenile survival in common loons Gavia immer: effects of natal lake size and pH.

Survival is a vexing parameter to measure in many young birds because of dispersal and delayed impacts of natal rearing conditions on fitness. Drawing upon marking and resighting records from an 18-yr study of territorial behavior, we used Cormack-Jolly-Seber analysis with Program MARK to estimate juvenile survival and its predictors in a population of common loons Gavia immer. In addition, we investigated predictors of chick mass, survival and inter-sibling size disparity in two-chick broods. Both small size and low pH of natal lakes predicted poor survival among chicks and juveniles; thus, features of the natal environment have both immediate and lasting effects on fitness. The pH × stage interaction retained in our MARK models indicates that the detrimental impact of lake chemistry on fitness diminishes with time; the retention of pH × lake size as a predictor of chick mass and condition pinpoints small lakes as those where acidity impacts chicks most severely. Our adjusted estimate of 0.53 probability of for survival to age 3 suggests that loon populations are healthier than often supposed. [ABSTRACT FROM AUTHOR]