Suspended highway beats road roulette for tiny critters

Suspension bridges allow small animals, such as dormice to cross busy roads safely. Photo / Getty Images

Above a road through a forest hangs a long, thin suspension bridge resembling a power line. Japanese dormice, small field mice and squirrels - forest-dwelling species that are recognised as national natural monuments - scramble along it as if it were just another tree branch.

Koichi Otake, 66, of Nerima Ward, Tokyo, who was an engineer for leading general contractor Taisei, is promoting a project for the construction of these suspension bridges, which are to be used by small animals inhabiting forests that have been split by development.

"They're just as cute as could be. I fell in love with dormice," Otake said with a sheepish grin. The dormouse is a rodent about 10cm long and weighing around 20g. It spends half of the year hibernating.

Otake's work at Taisei included geological surveys for the construction of dams and tunnels and technological development for road foundations. His first encounter with the dormouse came after he attended a work-related lecture by a researcher in small-animal protection.

When forests are cut to build roads, small animals like the dormouse find their environment reduced. If they try to cross roads, they frequently end up being hit by a car. When he learned about this, Otake thought that because his work involved the building of roads, "I should do something to keep the animals from being harmed," he said.

Before 2007, the only elevated pathway for small forest animals was in the Kiyosato Kogen highland in Yamanashi Prefecture. However, it cost ¥20 million ($250,000) to build. That year, Otake began putting his technical knowledge to good use and, after several attempts together with other construction engineers, hung a bridge measuring 7m-high, 25cm-wide and 13m-long above a city road in the same Kiyosato Kogen highland. By making the structure as simple as possible, they were able to keep construction costs at around 2 million - a figure within the range of even a small construction company.

After watching videos taken to verify the use of the bridge by small animals, Otake became keen to spread their use more widely. In May 2012, Otake founded the Animal-Pathway and Wildlife Association with other researchers and engineers.

The main work of the association is to spread the use of these pathways. Nationwide, 40,000 to 50,000 pathways are thought to be needed, but only five currently exist, located in Yamanashi, Aichi and Tochigi prefectures.

At Taisei, employees build nesting boxes for Japanese dormice to be used in ecology studies.