SEEN - SE European Bird Migration Network
Intra-seasonal variation in number of unmoulted coverts in Robins (Erithacus rubecula) migrating through the Polish Baltic coast
Małgorzata Ginter(1), Katarzyna Rosińska(1), Magdalena Remisiewicz(2)
1) Bird Migration Research Station, University of Gdańsk, Poland
2) Department of Vertebrate Ecology and Zoology, University of Gdańsk, Poland

The aim of our study was to show intra-seasonal variation in the number of unmoulted coverts in Robins (Erithacus rubecula) caught during autumn migration in 2002-200 at two ringing stations (Mierzeja Wiślana and Bukowo-Kopań) located at the Polish Baltic coast. In total data on 11 000 Robins were used. The analysis was done separately for each station in subsequent seasons. Firstly, seasonal trends of changes in mean number of unmoulted coverts were assessed. To explain these tendencies percentage distributions of wing spots each pentad were presented, grouped in three categories of according to the number of unmoulted coverts: 0-3 (low), 4-5 (medium), 6-8 (high). In addition, comparisons among pentads by Kruskal-Wallis and post-hoc Dunn’s tests were done, based on ungrouped data.
The same tendencies were observed within all seasons at both ringing stations: mean number of unmoulted coverts fluctuated in September, but from the end of this month and in October the trend was clearly increasing. This was due to changes in frequencies of the distinguished categories – in September birds with medium number of spotted coverts comprised over 50% of all migrants, while later individuals with high number of these coverts predominated.
These intra-seasonal differences in moult advancement can be explained by two phenomena – subsequent migration of populations with different moult characteristics and less advanced moult of birds from later broods. Observed trends correspond with literature data on migration timing of Robins of different breeding origin and winter quarters and indicate that the populational differentiation plays an important role in the observed variation.
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