We describe the development of Barnacle Goose Branta leucopsis breeding colonies in the Baltic area. The largest colony is situated on the eastern coast of Gotland. Sweden, and consisted in 1988 of 970 breeding pairs. Breeding birds have also been observed in nine other Baltic localities within the 1980s. Differences in reproductive success at different localities suggest that density-dependent effects are important. Young nonbreeding geese frequently move between colonies during the summer. Intraspecific competition may increase the propensity for natal dispersal by geese from the main colony on Gotland