SEEN - SE European Bird Migration Network
Morphological variation in the Robin (Erithacus rubecula) during autumn migration at the Polish Baltic coast
Katarzyna Rosińska(1), Małgorzata Ginter(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 this study was to show intra-seasonal variation in the leg colour in Robins. The material was collected during autumn migration at two Operation Baltic stations located on the southern Baltic coast –Bukowo-Kopań (in 2001-2004) and Mierzeja Wiślana (in 2002-2004). We determined leg colour in ca 10 800 immature Robins, according to the four-score scale (from pinkish to almost black legs) proposed by Pettersson et al. (1990) and modified by the authors.
We analysed frequencies of leg colour classes in all seasons at both ringing stations separately, with the G test. Leg colouration was compared between stations and seasons for birds from the whole season jointly, and than among pentads within seasons and between stations.
At Mierzeja Wiślana dark-legged birds (scores 3 and 4) predominated over other classes more than at Bukowo-Kopań. The tendencies of changes in leg colour categories proportions in subsequent pentads were visible at Bukowo-Kopań (except 2004 year). Birds with dark legs dominated at the beginning of the season and at the turn of September and October or in the first decade of October. At Mierzeja Wiślana this trend was unnoticeable and tendencies of changes in leg colour categories proportions were different every year. Only in 2004 year the sequence and timing of these trends were much more synchronised among the two stations.
The observed intra-seasonal changes in proportion of Robins with different leg colour we interpret as the result of subsequent migration of different populations through the Baltic coast. Comparison with literature data suggests that in September, i.e. during the period of prevalence of dark-legged Robins, most birds migrating through the Polish Baltic coast head to western winter-quarters. Domination of dark-legged Robins on the turn of September and October can be explained by occurrence of migrants heading to the Balkans, reported from this winter-quarter as having dark legs.  
Created by Pronetix 2006