Autumn Migration Dynamics of the Dunlin (Calidris alpina) at the Reda Mouth (Southern Baltic)

The study was conducted between 1996 and 2000 at one of the most important stopover sites for waders migrating along the southern Baltic coast. Everyday counts and trapping were performed between mid-July and the end of September. This period covered almost the whole period of adult migration, and a little more than a half of the total period of passage of juveniles. The majority of adults passed the study area between mid-July and the third decade of August. After this period adults were still observed among migrated Dunlins, but their number was rather small. In all seasons except 1996 second-year Dunlins migrated earlier than older birds, however migration periods of both groups overlapped to a large extent. First juveniles were recorded among migrating Dunlins as early as in the second decade of July. They belonged to the Baltic subspecies C. a. schinzii. The number of juveniles showed conspicuous increase not earlier than in the last decade of August, when birds of C. a. alpina arrived. The intra-seasonal changes in numbers of adults and juveniles showed a clear wavy structure. Two waves seem to be the most common pattern of juvenile migration in the Baltic area. Different factors which might influence the observed variation of migration patterns are discussed. Among them the most important aspects seem to be differences in migration timing between adult males and females and different geographical populations. Also local environmental conditions and weather situation on a route preceding a particular study site might influence the migration timing.