Wildlife corridors are man-made structures built to maintain the ecological passageways of animals around human structures like roads, railways or construction sites. Habitat fragmentation due to human development is a threat to biodiversity in today’s world, and wildlife corridors help animals migrate and interbreed.
Wildlife corridors over major thoroughfares have been built elsewhere in Europe since the 1980s, but Finland is just now waking to their potential. Several underpasses have appeared in the last few years, making it possible for animals to cross a busy road through a tunnel underneath.
A related solution is the idea of creating a dry path alongside the water in tunnels under roads that serve Finland’s myriad rivers and streams. Dry paths often already exist under bridges to make maintenance easier. They provide an important conduit for small animals to navigate without having to risk crossing the open road.
Over and under
But in terms of keeping the wildlife stock healthy and strong, purpose-built overpasses are the most valuable for larger mammals like elk and deer. This is because fences have been found to prevent them from migrating and colonizing new areas when food sources grow scarce.
A wildlife corridor over the Turku-Helsinki motorway near Lohjanharju has been in use in Finland for ten years. Markings on the ground in the stand of trees show that local animals have made good use of the safe passageway.
“There are mainly deer and rabbit tracks, a few fox have been through. The traces attest to the fact that the animals use this corridor well. We have seen many animals walking here, too. Especially once they start moving about again, they use this route. […] It is a natural passageway that elks normally use,” says Lars Hannu Åkerman of the local game management association.
Deadly elk collisions
A full-grown Eurasian elk, known as a moose in US English, can weigh up to 475 kilos at a height of two meters. The sheer mass of this largest animal in the deer family means that people in cars that collide with them are often killed instantly. Hunters often use this fact as a justification for culling the elk population in Finland.
A recent doctoral dissertation from Helsinki University researcher Milla Niemi has in fact found that the elk population is the most significant factor in traffic fatalities from elk-vehicle collisions. In the 2000s, the study finds, over ten people a year were killed in such accidents, while in the 2010s, that number has fallen to between zero and three a year.
The peak season for motor vehicle collisions with elk falls in September and October, with another peak noted in the late spring/early summer. As Finland’s spring arrives earlier each year, the peak has also moved accordingly.
A dry path alongside a waterway under a road is ideal for smaller mammals and reptiles, but still leaves larger creatures to try their luck crossing the road.
Dry paths are the way
The Hämjoki Bridge in southern Lohja looks like a standard underpass from afar, but closer inspection reveals its important function.
“Here you can see otter tracks, clear as day. He got out of the water and continued through the passage this way,” says Niemi, who will defend her thesis on April 1.
She says Finland has tens of thousands of these kinds of underpasses, only some of which have a dry path the animals can use.
“Dry paths are often left to assist with maintenance work and provide a buffer when there’s flooding. But they also help animals to navigate dangerous roads and railways safety, reducing the risk of dangerous accidents,” she says.
Culverts made of cheap galvanized steel are commonly used in Finland to allow water to flow under a road, railway or trails. Those that aren’t big or low enough to let larger animals through contribute to the death of an estimated million mammals each year, in addition to 200,000 reptiles, a million frogs and several million birds.
Because so many animals tend to move next to waterways, places where roads and water meet that aren’t equipped with decent underpasses are death traps for many animals.
Experiments have led Niemi to calculate in her dissertation that adding dry paths to every culvert would cut annual road kill by up to 80 percent.
“Anytime a bridge is repaired and it is possible to make it wider, it would be without a doubt beneficial to do,” she says.
The Finnish Transport Agency says the cost of building dry paths through tunnels during major road and railway projects is marginal, but large overpass wildlife corridors that serve larger mammals like elk are much more expensive to implement.