Variation in the Extent of Greater Wing Coverts Moult in Robins (Erithacus rubecula) Migranting in Autumn Through the Polish Baltic Coast

Abstract

Intra-seasonal variation in the number of unmoulted coverts in immature Robins caught during 2001-2003 autumn migrations was studied at two ringing stations (Mierzeja Wilana and Bukowo-Kopañ) located at the Polish Baltic coast. To determine the number of unmoulted greater wing coverts we counted immature-type coverts with light spots at tips. In the analyses data on the number of spotted coverts from ca 11 000 migrating individuals were used. We analysed the number of spotted coverts in each season and at each ringing station separately. Based on migration dynamics we distinguished migration waves and the number of spotted coverts were compared among the waves. Trends of seasonal changes in mean values of this parameter were assessed. To explain these tendencies, percentage distributions of wing spots for each wave were presented, with distinguished three categories: 0-3 (low), 4-5 (medium) and 6-8 (high) number of spotted coverts. Next, we compared distribution of this parameter among waves by Kruskal-Wallis and post-hoc Dunns tests. Late waves generally differed in the distributions of spotted coverts number from the earlier ones in all seasons and at all stations. Our results showed the same tendencies within a season in all cases: the mean number of unmoulted coverts fluctuated in September, but starting from the end of this month and in October the trend was clearly increasing. This was due to changes in frequencies of Robins assigned to the distinguished categories in September birds with medium number of spotted coverts constituted over 50% of all migrants, while in late September and/or October waves individuals with high number of spotted coverts predominated. Both in 2002 and 2003, the moment of the shift in this domination from birds with medium to those with high number of unmoulted coverts was synchronised between the two stations. These intra-seasonal differences in moult advancement can be explained by two overlapping phenomena subsequent migration over the Baltic coast of populations with different moult characteristics and by less advanced moult of birds from later broods. Correspondence of the observed trends in moult advancement with literature data on migration timing of Robins of different breeding origin and winter quarters indicates that the populational differences play an important role in the observed variation.

Biometrics Variation and Directional Preferences of Immature Robins (Erithacus rubecula) Caught in Northern Italy during Autumn Migration in 2005

“…In late migrants the reduction of the extent of greater coverts moult was observed amongst Robins caught at the Arosio Bird Observatory (unpublished data). Similar phenomenon was noted through the Polish and Swedish Baltic coast and north-western Russia (Karlsson et al 1986, Pettersson et al 1990, Rymkevich 1990, Ginter et al 2005. The authors explained this phenomenon by an inflow of birds coming from more northern breeding areas.…”

“…In some places like the stations located in Sweden or Norway some changes in wing length were observed (Mehlum 1981, Pettersson 1983, Pettersson and Lidholm 1983, Karlsson et al 1986. Variation in the number of unmoulted coverts is well known in young Robins caught during autumn migration in Sweden, Russia or Poland (Karlsson et al 1986, Pettersson et al 1990, Rymkevich 1990, Ginter et al 2005. Some studies showed intra-seasonal changes in directional preferences of Robins caught on autumn migration (ciborska and Busse 2004, Adamska and Filar 2005).…”

Autumn migration of robins (Erithacus rubecula) in Hungary

“…The second breeding can be the cause of the late migration of adults since the early migrating juveniles could originate from the first brood. The percentage ratio of migrants and the average recapture distance is greater in the case of the descendants originated from the first brood (Adriaensen 1986;Ginter et al 2005). The comparison of catch dynamics (t 10 and t 50 values) of juveniles and adults between study sites showed a higher similarity in the case of juveniles.…”

“…The birds that breed in Scandinavia migrate at the beginning of autumn, while the birds in northeastern breeding places start their journey only late in autumn (Ginter et al 2005). At the beginning, autumn migration of robins is oriented to more western wintering places then to the Apennine peninsula, eastern areas of the Mediterranean and lastly to the Balkans (Remisiewicz 2001;2002;Ściborska & Busse 2004;Adamska & Filar 2005;Adamska & Rosińska 2006;Meina et al 2007;Rosińska & Adamska 2007).…”