Autumn migration of the Long-tailed Tit (Aegithalos c. caudatus) at the opposite sides of the Eurasian continent

摘要

We compared autumnmigration in two distant populations of the nominate subspecies of the Long-tailed Tit (Aegithalos c. caudatus) with assumed different migratory habits in order to reveal the difference in characteristics of their movements. We studied the Northern European (Lake Ladoga region, NW Russia) population considered to be irruptive, and the Northeastern Asian (Primorye, Russian Far East) population which is believed to migrate regularly. We analyzed year-to-year fluctuation in numbers, timing of movements, body mass, fat reserves and plumage condition in migrating birds. We found that the two studied populations shared similar characteristics of autumn migration. Apart from significant fluctuations in numbers recorded in Northern Europe and Northeastern Asia, other features were similar to what have been observed for regular migrant species. Autumn movements of Long-tailed Tits in NW Russia and in the Russian Far East were registered every year and occurred in the dates specific to each population; the median date in different years spanned a two week period. In both populations, individuals that migrated later in the season gained larger fat reserves. Birds were involved in autumn movements either at the final stage of moult or just after the end of feather replacement. Our results indicate that Northern European and Northeastern Asian populations of Aegithalos c. caudatus show similar patterns of migratory behaviour.