Nearly all of Helsinki’s nature areas are important bat habitats. Bats (Chiroptera) favour old buildings, hollow old trees, ponds and inlets that are protected from the wind as well as sparse forests with clearings.
There are five bat species that are commonly found in Helsinki. The most prevalent of these is the northern bat (Eptesicus nilssonii). The grey long-eared bat (Plecotus auritus) is easy to distinguish from other bats by its long ears, as the name implies. The whiskered bat (Myotis mystacinus) and the Brandt’s bat (Myotis brandtii) are so alike that it wasn’t until the 1960s that they were discovered to be two different species. The Daubenton’s bat (Myotis daubentonii) usually hunts over water.
Bats can be observed with the help of bat detectors, which record, distinguish and convert their echolocation signals into sounds audible to the human ear. Bats are also caught with hoop nets for study purposes and tagged, just like birds.
In one August night in Vallisaari in 2016, researcher Eeva-Maria Kyheröinen caught approximately two dozen bats to study: northern bats, grey long-eared bats, whiskered bats and Brandt’s bats. The caves among the fortifications of Vallisaari have been found to house hibernation colonies consisting of dozens of whiskered bats.
Many bat species migrate, leaving Finland and crossing the sea to warmer regions for the winter, just like birds. Their migration is studied using bat detectors.