The Siberian flying squirrel (Pteromys volans) spread back to Helsinki from the direction of Espoo in the 2010s, to the surprise of many. It has since settled in the forests of Meilahti, Munkkivuori and Central Park, and is continuing to spread eastward. The Siberian flying squirrel needs large trees, such as spruces and aspen, to make its nest in, as well as young border forests to forage in. It has adapted well to many semi-natural urban forests.
The Siberian flying squirrel spends its days sleeping in a hole excavated by a woodpecker, only stirring at the arrival of dusk. Spotting a Siberian flying squirrel takes no small amount of luck. In late winter/early spring, you can track them by the yellow droppings that they leave at the bases of trees. During their mating season in April–May, Siberian flying squirrels have been spotted in the Pirkkola Sports Park, among other places.