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Open access

Małgorzata Ginter, Katarzyna Rosińska and Magdalena Remisiewicz

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

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 Wiślana and Bukowo-Kopań) 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 Dunn's 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.

Open access

Łukasz Meina, Małgorzata Ginter and Katarzyna Rosińska

Stopover of Robins (Erithacus rubecula) On Autumn Migration Through the Polish Baltic Coast

Data were collected during autumn migration at three ringing stations of the Operation Baltic: Bukowo-Kopań, Mierzeja Wiślana and Hel. Apart from different localization at the Polish Baltic coast, these places differ also in topography and habitat. Only data from years with the highest number of caught birds were used in the analyses, thus altogether the data on more than 25 500 ringed Robins and 1700 retraps were included. Based on migration dynamics graphs and number of retraps, a stopover index was calculated. Next, the index values were compared between days with a high and low number of caught birds and also between different fat categories. Differences between birds caught once and retraps were shown in relation to daily activity, age structure and fat level. Additionally changes in weight and fat level between first and last control in retraps were considered. At Mierzeja Wiślana and Hel the stopover index decreased in the course of autumn season in contrast to Bukowo-Kopań where an increasing trend was observed. At Bukowo-Kopań more birds decided to stopover than at Mierzeja Wiślana and Hel but at Mierzeja Wiślana Robins stayed longer than at other stations. Moreover, at Mierzeja Wiślana a half of departing retraps increased in fat level while at the other stations only ca 20% of retraps. Our results showed that in Robins the weak body condition is a decisive factor to stopover after crossing the sea. Differentiation in food resources and competition between individuals had an effect on the stopover index. Stopover duration at different ringing stations can depend on distance which birds cover before landing at the coast.

Open access

Jarosław Nowakowski, Jacek Chruściel, Małgorzata Ginter and Katarzyna Rosińska

Any change in the Methodology of field studies on bird Migration? A comparison of methods used in 1994-2003 and a Quarter Century earlier

The holistic approach to the study of bird migration observed in the past decades and the huge advancement in technology should be seen in the numbers and types of methods used in field studies for this phenomenon. To check this assumption, we compared field methods used in the studies on bird migration published in international journals in 1994-2003 (N = 570 papers) and in 1967-1976 (N = 394 papers). We noted an increase in the mean number of methods per a single paper (from 1.49 in the former of these decades to 1.98 in the latter) and a change in the frequency of each method. In recent years, methods such as satellite telemetry, DNA or isotope proportions analyses have been developed. An increase in the mean number of methods as well as changes of the most frequently used methods were more apparent in journals indexed on the ISI Master Journal List in 2003 than in other current journals, where the methods were often found to be similar to those applied a quarter century earlier, which surprised us.