New migratory habits in Swedish Greylag geese: a challenge for flyway management?

The growth of some European goose populations spurs initiatives to manage them at the flyway level. Success of such endeavors build on an appreciation of migration routes and temporal distribution. We describe movements over the annual cycle in 76 Greylag geese (Anser anser) fitted with GPS tracking devices at five sites in Sweden. Swedish Greylag geese still use a general SW-NE migration path. However, compared to previous knowledge we show that their wintering range has undergone a northward shift and a general reduction in migration distance, most pronounced in birds breeding in southernmost Sweden. The latter spent almost the entire annual cycle in Sweden and Denmark. The flyway of Greylag geese from more northern capture sites, though, still covers countries from Sweden to Spain, but only a fraction of the population now migrates to Spain. Instead, most of the annual cycle is spent in Sweden, Denmark, the Netherlands or Germany. Analyses based on the net squared displacement modelling framework show that Swedish Greylag geese now display ‘a leapfrog migration pattern’, radically different from ‘the chain migration pattern’ evident for the same population 35 years ago. The contrasting spatiotemporal distribution in geese of different geographical origin shows that management initiatives for European Greylag Geese must consider that different migration patterns occur within previously defined management units. As a consequence, coordination of management actions (monitoring, harvest quotas, reserves) needs to consider different spatial scales, from the regional to international, depending on the origin of the Greylag geese.