Bats can be found throughout mainland Finland, from Hanko to Utsjoki, but no-one really knows how many of them there are. During the day they rest in hiding, emerging at nightfall when most humans are indoors or sleeping.
Next weekend is a good time to look into the evening skies though, as the Finnish Chiropterological Society Finland is arranging a national bat-spotting event.
The group is asking interested members of the public to spend an hour outdoors around dusk and report on any bat sightings by filling in a Finnish-language questionnaire (siirryt toiseen palveluun) on their website. Researchers hope to gather more comprehensive information on Finland’s 13 bat species and their habitats with the effort.
The project does not require any advance knowledge of bats. Simple reports of visual observations are sufficient. Those with more of an interest in bat monitoring can also buy a bat detector for a starting price of around 80 euros.
The detector converts bats' echolocation ultrasound signals into sounds that are audible to human ears," says Thomas Lilley, the Finnish Museum of National History's mammal curator, who appeared on Yle's morning show on Tuesday.
“The sounds are basically clicks. Based on these, you can differentiate one species from another. For example the northern bat has a very characteristic clicking,” he explains.
Active from dusk to dawn
The best moment for batwatching is 30-45 minutes after sunset – shortly after 10 pm in southern Finland at present – when bats head out to feed.
During the day, bats prefer to hang out in the attics of old wooden houses, birdhouses or holes in trees.
“For instance a Daubenton's bat may take over a birdbox that has been vacated by flycatchers or tits. A telltale sign that bats have settled in a tree hole is if there are flies buzzing around the entrance. In the case of old houses, droppings along the edge of the roof are a sure sign of bats,” Lilley says.
Bats can also be identified during the day by their sounds, as they do not always sleep and sometimes squabble loudly.
“Bats like to be in a tight group. But sometimes they have disputes, during which they make grating sounds,” says Lilley.
Bats can beat the heat
According to Lilley, the current heat wave is not generally a problem for bats, who seem to enjoy the warmth.
“Bats are good at finding good living conditions,” he says. “They may move to a lower position if they get too warm, for example. They’re also good at finding drinking water.”
Sometimes humans might come across a baby bat on the ground. Lilley says they should never be touched with bare hands, because bats can bite and may carry infectious diseases.
“If you find a pup, put on leather gloves, try to see where it fell from, say, a hole in the edge of a roof, and carefully try and put it back.”