SEEN - SE European Bird Migration Network
Stopover of Robins (Erithacus rubecula) during autumn migration through the Polish Baltic coast

Małgorzata Ginter, Katarzyna Rosińska, Łukasz Meina

Bird Migration Research Station, University of Gdańsk, Poland

During the Operation Baltic fieldwork in autumn birds were caught at three ringing stations: Bukowo-Kopań, Mierzeja Wiślana and Hel. Despite different localisation at the Polish Baltic coast, these places differ also in topography and habitat. The aim of our study was to compare stopover duration, body condition (fat deposition, body weight) and age structure of the Robins caught at these stations. In our analyses we used data from years with the highest number of caught birds, thus in total, data on 15 500 ringed Robins and 1 700 retraps were included. Based on the migration dynamics graphs, a stopover index was evaluated. This index was compared between three categories of days: peak days (the highest number of caught birds), days neighbouring the peak days and days with the lower number of caught birds. Comparisons between the stopover index and fat categories were also done.
The obtained results showed that at Bukowo-Kopań more birds decided to stop over than at Mierzeja Wiślana and Hel but at Mierzeja Robins stayed longer than at other stations. Moreover, among retraps caught at Mierzeja there was higher proportion of adult birds than at Kopań and Hel. At each station the stopover index was lower in the peak day than in the neighbouring ones. At Mierzeja Wiślana the stopover index decreased in the course of the autumn season, in contrast to Bukowo-Kopań where an increasing trend was observed. At all analysed stations the stopover index was lower, the higher the fat class was. At Bukowo and Mierzeja the highest stopover index was observed when the fat level was the lowest. At Mierzeja Wiślana more birds departed with higher fat reserves than at Bukowo and Hel.
Our results showed that poor body condition is a decisive factor to stop migration and stay longer in stopover places after crossing the sea. Differences in stopover duration between ringing stations depend on distance which birds cover before landing at the coast.

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