Different timing of autumn migration of two Ringed Plover Charadrius hiaticula subspecies through the southern Baltic revealed by biometric analysis

Abstract

Ringed Plovers were trapped in Puck Bay (southern Baltic) between 1983 and 2002 during autumn migration. In adults a clear decrease of mean wing and bill lengths occurred between the third decade (ten‐day period) of July and the first decade of August. A similar pattern was observed in juvenile wing lengths, whereas a sharp decline in mean bill length occurred later, between the second and the third decade of August. These changes in biometrics suggested that the larger birds passing through the study area in July belonged to the hiaticula subspecies and late migrants (adults caught from the beginning of August and juveniles caught from the third decade of August) were of the tundrae subspecies. This was supported by comparison of mean measurements of these early and late migrants passing through Puck Bay with data from other areas where only either hiaticula or tundrae occur. These data were used to compare the biometrics of adults and juveniles of each subspecies.