Migration of Black Storks Ciconia nigra at a migratory divide: two different routes used by siblings from one nest and two different routes used by one individual

ABSTRACT Black Storks Ciconia nigra breeding in Europe use two main migratory routes to winter in Africa: a western route over Gibraltar and an eastern route through Turkey and Israel. A broad area of migratory divide exists in central Europe. We examined cases from the Czech Republic wherein siblings from one nest used different migration routes. We found 20 such cases associated with 18 nests distributed throughout the entire territory of the Czech Republic. Moreover, one bird hatched in 2007 used the western migration route in 2007 and the eastern one in 2009. The actual geographical position of a juvenile Black Stork from an area of migratory divide in the autumn period of migratory restlessness (after the dispersal period) influences the decision to choose the western or eastern direction of migration. We also propose that Black Storks that are older than one year and therefore with experience of past migrations could decide their direction of autumn migration and be followed by inexperienced juvenile Black Storks. Siblings originating from an area of migratory divide can commonly use both main migration routes.