Travels and traditions: long-distance dispersal in the Barnacle Goose Branta leucopsis based on individual case histories

Long-distance dispersal can have far-reaching consequences for the amount of gene flow between populations. However, individuals usually disperse to places well outside the study area, which makes long-distance dispersal hard to study. In this study, the fate of c. 4500 individually marked Barnacle Geese Branta leucopsis hatched on the Swedish island of Gotland between 1984 and 2002 was followed. Only 18 dispersed to other Barnacle Goose populations along the flyway, 16 males and two females. Most long-distance dispersers were very large compared to other cohort members, and were observed to become independent of parents and siblings early in life. It is estimated that about 6.6% of all juvenile Barnacle Geese disperse over long-distances, but at most 11% of these long-distance dispersers were actually detected. Most dispersed to the large Russian population, where several birds were observed breeding and/or retrapped during fieldwork between 2002 and 2004. One male dispersed from Gotland to the Svalbard population. Breeding was only proven in three out of the 18 dispersers, and only one is known to have successfully fledged young. These results confirm that many years of intensive studies at different localities are needed to define long-distance dispersal rates