The European tree frog

When scientists began a simple pond-building campaign, the populations of all of Switzerland's vulnerable frog species 'exploded.'

Among the web-footed benefactors was the European tree frog, whose population has doubled since 1999, as has the number of regions where it can be found.

While the Swiss canton of Aargau has strong protection regulations for their frog, newt, and toad species, scientists wanted to test if habitat restoration may help their steadily dropping numbers.

A 20-year program of establishing 422 ponds across five Aargau areas began in 1999, in collaboration with the Aargau government, non-profits, volunteers, and landholders.

Most frogs require little ponds that naturally form along the sides of bends in gently meandering rivers, features that have rapidly vanished in Switzerland's dense road/railway network, and carefully maintained farms.

52% of the eight endangered species' regional populations rose, while 32% stabilized.

The European tree frog was one of the species that experienced a particularly robust resurgence. This small frog can travel many kilometers in search of a suitable environment to lay its eggs.

Because predator species eventually make their way into existing ponds to prey on their tadpoles, frogs require new ponds to relocate to.

These predators frequently occupied the few ponds that existed prior to the project.

The experts believe that the simple act of constructing ponds can aid in the restoration of amphibian populations in human-dominated areas.