Abstract
Between 1983 and 2001, altogether 593 juvenile Ruffs were caught and measured during autumn migration in Puck Bay region. The wing length is the best predictor of sex in juvenile Ruffs. Relatively small differences between sexes in bill and nalospi length imply that males and females forage in a similar manner. However, longer legs in males allow them to forage in deeper water than females.
The comparison of biometrics of juvenile Ruffs caught in different regions indicates that Ruffs from western populations are larger than their conspecifics breeding farther to the east. Slight decrease of mean measurements within the season in juveniles trapped in Puck Bay suggests that Ruffs from more western breeding areas pass study area earlier followed by birds originating further east.
Body mass adjusted for the size increased significantly along the season in males and in females. Thus, similarly to some other juvenile waders, Ruffs that stopped in Puck Bay region migrated with small energetic reserves. However, later migrating birds of both sexes had larger energetic stores than earlier migrants, which could allow them to make longer nonstop flights.