The barnacle goose (Branta leucopsis) used to nest only in Arctic areas. However, in the 1970s it settled on the Swedish island of Gotland, from where it has since continued to spread widely around the Baltic Sea. In Helsinki, the species started nesting around the same time as the Canada goose.
Nowadays there are approximately 700 pairs of barnacle geese nesting in Helsinki. Unlike the Canada goose, the barnacle goose nests mostly in colonies located on islets out at sea. From April to October, you can see flocks consisting of hundreds of barnacle geese flying in the skies over Helsinki. In September, when the goslings take wing, barnacle geese gather into massive flocks consisting of up to a thousand birds, feeding on fields and assembling to sleep in Vanhankaupunginlahti, among other places.
While a small breeding population of barnacle geese formed on the west coast of Estonia in the 1980s, the species is mostly an Arctic migrant in the country. This is due to the fact that Tallinn and the northern coast of Estonia lack kind of islets that barnacle geese nest on. The barnacle goose does not nest on mainland shores due to foxes and other terrestrial predators.