Age–specific access to high–quality resources (e.g. territory or nest site) might be an important determinant for improved reproductive performance with increasing age. I experimentally investigated the effects of territory quality versus other age–related improvements in breeding competence (e.g. foraging skills, breeding experience and local knowledge) on age–specific reproductive success. Territory quality (i.e. territory field layer height) was manipulated in year 2 of northern wheatears (Oenanthe oenanthe) that were breeding in the same territory in two consecutive years. Changing territory quality by changing field layer height had a strong effect on within–individual change in the reproductive success of wheatears. This effect was mainly due to a corresponding change in nest predation risk. When territory quality was kept constant (i.e. no between–year change in territory field layer height), within–individual reproductive success did not change between subsequent years. Thus, age–related improvements in foraging skills, breeding experience and local familiarity had no significant effect on within–individual changes in reproductive success. Increased reproductive success with increased age in northern wheatears is therefore mainly explained by an improved access to high–quality territories with increasing age. I conclude that age–dependent access to high–quality breeding resources might be a widespread phenomenon in nature.