Abstract
Characteristics of the intra-populational variation of morphological parameters in the Savi's Warbler is based on measurements of 512 individuals caught in the breeding seasons of 1989-1998 in the Bagno Ławki peatbog (the southern basin of the Biebrza river valley). In the studied population, adult Savi's Warblers had longer and more rounded wing, longer tail and larger body mass than young individuals. Moreover, significant differences in the length of allula and 1st primary were found between these age classes. The range of wing length noted in this population, with the maximum value of 78 mm, distinctly exceeded the range of this parameter described for European populations of the Savi's Warbler. The average lengths of wing, tail allula and tarsus were distinctly higher in males than in females. Sexes did not differ in body mass, Kipp's distance and wing pointedness index. In the studied population, a distinct long-term variability of tail length, Kipp's distance, wing-tip pointedness index and tarsus length was found in young birds. In adults such variability was found only in tarsus length. The paper discusses possible reasons for the long-term variability of studied parameters.