Biometrics of the Dunlin (Calidris alpina) Migrating in Autumn Along the Polish Baltic Coast

The aim of this study is to present the general biometrical characteristics of Dunlins passing the Polish Baltic coast during autumn migration. Data were collected between the first week of July and the end of September in 1991-2002. Comparison of the mean wing lengths of Dunlins from different regions revealed that birds migrating through the Puck Bay had on average shorter wings than those trapped in areas located more south-easterly and clearly longer than those from Mauritania. In adults, seasonal variation of mean bill and wing lengths showed sigmoid pattern with larger birds in July at the beginning of migration and in mid-September. Such pattern is typical for this species, because females, which are larger than males, migrate earlier. Similar pattern of seasonal changes of mean bill and wing lengths might be noted in second-year birds. Juveniles caught in July must have belonged to local population of C. a. shinzii, which is smaller than the nominative subspecies. The sample of juvenile birds trapped in the beginning of August probably consisted of individuals from both subspecies, which resulted in the lower mean values of wing and bill lengths. Changes in the size of juveniles from year to year might be caused by differences in food availability on the breeding grounds, e.g. due to weather conditions.