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.